\r\n\t
\r\n\tRecently in 2019, International Council on Systems Engineering (INCOSE) has released the latest version of the “Guidelines for the Utilization of ISO/IEC/IEEE 15288 in the Context of System of Systems (SoS) Engineering” to industry for review and comments. The document was developed under the Partner Standards Development Organization cooperation agreement between ISO and IEEE, as it was approved by Council Resolution 49/2007. This document provides guidance for the utilization of ISO/IEC/IEEE 15288 in the context of SoS in many domains, including healthcare, transportation, energy, defense, corporations, cities, and governments. This document treats an SoS as a system whose elements are managerially and/or operationally independent systems, and which together usually produce results that cannot be achieved by the individual systems alone. This INCOSE guide book perceives that SoS engineering demands a balance between linear procedural procedures for systematic activity and holistic nonlinear procedures due to additional complexity from SoS perspectives.
\r\n\tThe objective of this book is to provide a comprehensive reference on Systems-of-Systems Engineering, Modeling, Simulation and Analysis (MS&A) for engineers and researchers in both system engineering and advanced mathematical modeling fields.
\r\n\tThe book is organized in two parts, namely Part I and Part II. Part I presents an overview of SOS, SOS Engineering, SOS Enterprise Architecture (SOSEA) and SOS Enterprise (SOSE) Concept of Operations (CONOPS). Part II discusses SOSE MS&A approaches for assessing SOS Enterprise CONOPS (SOSE-CONOPS) and characterizing SOSE performance behavior. Part II focuses on advanced mathematical application concepts to address future complex space SOS challenges that require interdisciplinary research involving game theory, probability and statistics, non-linear programming and mathematical modeling components.
\r\n\tPart I should include topics related to the following areas:
\r\n\t- SOS and SOS Engineering Introduction
\r\n\t- Taxonomy of SOS
\r\n\t- SOS Enterprise (SOSE), SOSE CONOPS, Architecture Frameworks and Decision Support Tools
\r\n\tPart II should address the following research areas:
\r\n\t- SOS Modeling, Simulation & Analysis (SOS M&SA) Methods
\r\n\t- SOS Enterprise Architecture Design Frameworks and Decision Support Tools
\r\n\t- SOS Enterprise CONOPS Assessment Frameworks and Decision Support Tools.
During the last few decades, mobile communication has evolved significantly from early wireless voice systems to today’s intelligent communication systems [1, 2]. With the advancement of each generation, the mobile communication systems become more sophisticated and unleashed new consumer services that support countless mobile applications used by billions of people around the world, shown in Figure 1 [1, 2, 3]. In 2000, when 3G brought us the wireless data, the consumers got access to the internet anytime and anywhere they go [2]. This mobile broadband network with a combination of the innovation of smartphone technologies brought a significant change of mobile internet experience where users can access their email, social media, music, high definition video streaming, online gaming, and many more, which we see today as the app-centric interface [4].
\nThe evolution of mobile standards [3].
Due to the advancement of technologies, mobile devices getting smarter every day in terms of advanced computing and multimedia capabilities that supports a wide range of applications and services (e.g., high quality image transfer, ultrahigh definition video streaming, live video games, and cloud resources) [5, 6]. Therefore, more and more users are expecting to have the same quality of internet experience anytime, and everywhere they go. These trends will even more pronounced when 5G network becomes available with intelligent network capabilities and numerous services. 5G network will extend the wireless connectivity beyond the people, to support the connectivity for everything that may benefit from being connected that might include everything from personal belongings, household appliances, to medical equipment, and everything in between [1]. Numerous 5G network use cases, services and network requirements are discussed in [7]. Here are the two most significant trends of 5G services are discussed below [6]:
Everything will be connected to the mobile network wirelessly that will enable the billions of smart devices interconnected autonomously while ensuring the security and privacy [8]. 5G network will enable emerging services that include remote monitoring and real-time control of a diverse range of smart devices, which will support machine-to-machine (M2M) services and Internet of Things (IoT), such as connected cars, connected homes, moving robots and sensors [6, 8, 9, 10]. According to Cisco VNI Mobile 2017, the most noticeable growth will occur in M2M connections. The number of M2M connection will reach 3.3 billion by 2021, which is 29% of the total devices and connections and it was only 10% in 2016 [5]. Another mobile traffic forecast by UMTS presented that the total number of connected IoT devices will reach to 50 billion by 2020 which was only 12.5 billion in 2010 [5].
5G networks will deliver richer content in real time ensuring the safety and security that will make the wireless services more extensive in our everyday life. Some example of emerging services may include high resolution video streaming (4K), media rich social network services, augmented reality, and road safety [6]. According to Cisco mobile data traffic forecast, the maximum mobile data traffic will be generated by video-based mobile application, which is going to be 72% of mobile data traffic by 2019 compared to 55% in 2014 [5, 11].
It is clear that the future mobile network (i.e., 5G) will no longer human centric, it will be more on machine centric which will interconnect billions of smart devices to the mobile network. According to Cisco, smart devices are those that have advanced computing and multimedia capabilities with a minimum of 3G network connectivity [5]. Globally the growth of smart devices will reach 82% by 2021 and some regions it will reach 99% by 2021 (e.g., North America). The main impact of this growth will be on mobile data traffic because a smart device generates much higher traffic compared to non-smart device. According to Cisco forecast, a smart device generated 13 times more traffic compared to non-smart device in 2016 and by 2021 a smart device will be able to generate 21 times more traffic [5]. According to another mobile traffic forecast by Cisco, the expected growth will reach 24.3 Exabytes per month by 2019 which was only 2.5 Exabytes in 2014 [12]. This ever-increasing traffic growth becomes the key driver for the evolution of next generation mobile networks, called 5G, envisioned for the year 2020 [13, 14]. The key requirements of 5G network include, extreme broadband delivery, ultrarobust network, ultralow latency (i.e., less than 1 ms latency) connectivity, and support massive smart devices for the human and for the IoT services [15].
\nTo bring the 5G network in reality, a simple upgrade of mobile network will not be enough where we just add new spectrum and enhance the capacity or use advanced radio technology. It will need to upgrade from the system and architecture levels down to the physical layer [15]. Although some research and standardization work addressing the corresponding challenges from radio perspective (e.g., new spectrum exploration, carrier aggregation, network densification, massive multiple-input-multiple-output, and inter-cell interference mitigation techniques) but there is a new challenge has emerged: the backhaul [16, 17, 18]. Because in 5G networks, the ultradense and heavy traffic cells will need to support hundreds of gigabits of traffic from the core network through backhaul and today’s cellular system architecture is infeasible to meet this extreme requirement in terms of capacity, availability, latency, energy, and cost efficiency [16, 19].
\nA details survey about the evolution of mobile backhaul solution from 2G to 3G networks and from 3G to 4G networks are presented in [20, 21], respectively. The hybrid of millimeter wave and optical backhaul solution is proposed in [22] where the software-defined backhaul resource manager is proposed as a novel software defined networking (SDN) approach for realizing high utilization of the backhaul network capacity in a fair and dynamic way, while providing better end-to-end user quality of experience (QoE). Also, [23] provides another hybrid solution that combines an optical laser (through free space) and millimeter-wave radio to provide a combination of guaranteed high capacity, extended reach, and high availability with affordable cost.
\nIf given a choice, fiber always remains the first backhaul choice for service provider due to its inhibitive bandwidths more than 10 Gbps and allowed maximum latency of hundreds of microseconds [16, 23]. But, laying fiber to connect all the cells to the core is not possible in some cases due to the availability problem and the deployment cost is high as well. In addition, fiber deployment, even when it is feasible can take several months [4, 23]. Since the massive deployment of small cells will be the key techniques for 5G networks and the backhaul requirements of the small cells can significantly vary with the small cell location, the fiber cannot be the optimal approach for 5G backhaul solution [23, 24, 25]. On the other hand wireless backhauling (e.g., microwave and millimeter wave) becomes popular due to its availability, deployment time and cost-effective approach [24]. But the weather condition and multipath propagation have significant impact on microwave and millimeter-wave radio systems which can affect the transmission performance. So it is obvious that there will no unique backhaul solution for 5G networks. The backhaul evolution for 5G networks will include both wired and wireless backhaul solution [23].
\nThe contributions of this book chapter are listed below:
First, this chapter provides a brief introduction of mobile backhaul network and the evolution of mobile backhaul network.
Second, provides a comprehensive overview of backhaul requirements of 5G networks and highlight the potential challenges.
Finally, it outlines the existing mobile backhaul solutions (i.e., wired and wireless) and list their features, benefits, drawbacks, application areas and deployment challenges.
The mobile backhaul network connects radio access network air interfaces at the cell sites to the inner core network which ensures the network connectivity of the end user (e.g., mobile phone user) with the mobile networks (shown in Figure 2). In Figure 2, UE refers to end user, eNodeB refers to cell or cell site or base stations. Each user data is added with other components of the backhaul traffic (shown in Figure 3), to calculate the single eNodeB transport provisioning and then aggregate with all other eNodeB’s traffic before it connects with the core network.
\nMobile backhaul network of LTE (long-term evolution) [26].
Components of backhaul traffic [26].
It is found that the capacity requirements on the transmission network to support the backhaul traffic from the core network is raises with the evolution of mobile/cellular networks [23]. Cost and reliability always been a concern and major challenges for cellular network operators and there is no magic solution to the demand [19]. This section describes, how the mobile backhaul network evolve with the evolution of each mobile network (e.g., 2G, 3G, and LTE).
\nA typical GSM (Global System for Mobile Communications) network architecture is shown in Figure 4, where the BTS (base station transceivers) are located at the cell site and provide the control and radio air interface for each cell. The BSC (Base station controllers) provides control over multiple cell sites and multiple base station transceivers. The base station controllers can be located in a separate office or co-located at the mobile switching center (MSC).
\nTypical GSM network with wireless interface requirements [27].
There are standard interfaces developed by the wireless industry for interconnecting these devices, so they could deploy interoperable systems from multiple vendors. These physical interfaces define the wireless backhaul transport services and requirements. Thus, a basic understanding of these interfaces is very important. Some standard interfaces for GSM network are listed below [27]:
Abis: the Abis interface connects the base station transceivers to base station controllers.
A: the A interface in Figure 2 connects the base station controller to the mobile switching center.
Gb: voice services continue over the A interface, while data services are handled over the Gb interface.
Although the functions of these devices are similar, the 3GPP wireless standards body adopted slightly different names for the functional nodes and logical interfaces for UMTS (3G) networks, shown in Figure 5. But, historically the 2G/3G wireless standards were based on T1 (TDM) physical interfaces for interconnection between these devices because of the wide availability of T1 copper, fiber, and microwave services [28].
\nTypical 3G network with wireless interface requirements [27].
T1 physical interfaces has driven mobile backhaul transport requirements for 2G/3G wireless standards, but 4G wireless standards (i.e., LTE: Long-Term Evolution) are based on entirely new packet-based architecture, including the use of Ethernet physical interfaces for interconnection between the various functional elements, shown in Figure 6.
\nTypical LTE network with wireless interface requirements [28].
Another objective of the LTE standards was to flatten and simplify the network architecture. This resulted in pushing more intelligence into the radios (eNodeB) and elimination of the radio controllers as a separate device. In effect, the radio controller function has been distributed into each eNodeB radio. So, the resultant network is indeed much simpler and flatter, with far fewer functional devices.
\nFrom a mobile backhaul perspective: most cell sites will continue to support GSM 2G and UMTS 3G networks for many years, the addition of LTE means backhaul transport carriers need to implement systems that can support both native T1 TDM services and Ethernet services. But, the major changes are the higher capacities required by LTE cell sites. A detail comparison of wireless capacity requirements for 2G, 3G, and LTE networks are shown in Table 1.
\nStandards | \nVoice spectrum (MHZ) | \nData spectrum (MHZ) | \nVoice spectral efficiency (bits/Hz) | \nData efficiency (bits/Hz) | \n# Sectors | \nTotal bandwidth (Mbps) | \n# T1 s | \n
---|---|---|---|---|---|---|---|
GSM 2G | \n1.2 | \n\n | 0.52 | \n\n | 3 | \n1.3 | \n1 | \n
GSM/EDGE 2.75G | \n1.2 | \n2.3 | \n0.52 | \n1 | \n3 | \n6.1 | \n4 | \n
HSDPA 3G | \n\n | 5 | \n0 | \n2 | \n3 | \n21.0 | \n14 | \n
LTE 4G | \n\n | 5 | \n0 | \n3.8 | \n3 | \n39.9 | \nn/a | \n
LTE 4G | \n\n | 10 | \n0 | \n3.8 | \n3 | \n79.8 | \nn/a | \n
Enhance the network reliability and reduce the cost efficiency always been a major challenge for the cellular network operator and there is no magic solution to that demand [19]. With the evolution of mobile network, the capacity requirement of the transport network from the core raises significantly [23]. The major backhaul challenges that mobile network operator had to deal with up to 4G network includes capacity, availability, deployment cost, and long distance reach [16]. But, 5G network will interconnect billions of new start devices with the numerous use cases and services, which will support machine-to-machine (M2M) services and Internet of Things (IoT) to the mobile network [6, 8]. These new smart devices will not only enhance the backhaul capacity requirement, but it will also add two additional challenges in the backhaul network: (a) ultralow latency of ∼1 ms (round trip) connectivity requirements, and (b) denser small cell deployment. This section describes the 5G backhaul requirements and potential challenges.
\nThe evolution of 5G cellular network is positioned to address new services and demands for business contexts of 2020 and beyond [29]. It is expected that 5G network will enable a fully mobile and connected society that empower socio-economic transformation in many ways and even some of which are unimagined today. To fulfill the demand of fully mobile and connected society can be characterized by the tremendous increase in the number of connectivity and traffic volume density [29]. According to Nokia, the number of connecting devices per mobile users will be ten to one hundred that includes, mobile phone, laptop, tablet, smart watch to smart shirts [11]. In addition, the number of connected machines and sensor devices in the industry and public infrastructure will increase. According to Ceragon, the forecasted capacity increase could be ×1000 compared to the capacity density in current 4G/4.5G networks [30, 31]. So, it is obvious that the evolution of 5G networks from LTE/LTE-A will need higher capacity backhaul links per cell site: while LTE/LTE-A networks need hundreds of Mbps, 5G network will need to support tens of Gbps, shown in Figure 1.
\nAvailability is the major consideration for any backhaul networks, if the backhaul services are not in operation the system performance are negatively affected. In case of fiber systems, if there is any interruption of current path, the systems will automatically switch to the protection path within <50 ms [23]. Even in the wireless backhaul (e.g., microwave and millimeter wave), the backhaul link can be affected by multipath propagation and bad weaher condition. To overcome this, adaptive modulation technique is used that lowers the line rates to maintain the availability. Although the 5G network requirements is not standard yet, but to provide the expected new services such as autonomous vehicle/autonomous driving, tactile internet, and many machine to machine applications need high availability and very low latency [30].
\nCellular network provider has to spend billions of dollars each year to acquire wireless spectrum for building excellent network coverage [23]. Since dense small cell deployment will be the key for 5G networks to support 1000 times more capacity, the cost efficient backhaul solution for the small will be a major challenge. An application specific traffic-engineering model needs to be formulated so that both customers and service providers can be happy.
\nReach defines how far a cell site can get backhaul support from the core network with the required quality of service. Long distance reach is always a big issue for the backhaul network in terms of cost and additional equipment (e.g., total deployment cost of fiber backhaul will increase with the distance) [23]. Typically, cell sites are interconnected in a hierarchical mesh and all the traffics are transported back to an aggregation point (sometimes-called super cell) where all the traffics are aggregated and transport to the core network. Due to the dense small cell deployment in the 5G networks, massive backhaul traffic will be aggregated at the super cell that can create congestion and can even collapse the backhaul networks [19]. Therefore, long distance reach will be a big challenge for the 5G backhaul network.
\nOne of the major requirements of 5G network is ultralow latency ∼1 ms (round trip) [31]. Some 5G use cases and services, such as real-time monitoring and remote control, autonomous driving, tactile internet, and M2M applications need to support by mission-critical network because this type of services will need high availability, ultralow latency and tight security. In addition, the risks of network failure are too high [30]. Therefore, it will be a big challenge for 5G backhaul to support massive traffic and maintain the required quality of service with lower latency requirement. Since propagation delay is inherent, a solution has to be formulated based on physical layer.
\nSince, 5G will use higher RAN frequencies, the cell site coverage will become very small compared to today’s cell site (i.e., macro or micro cell). It is also not feasible to increase the cell site capacity by 1000 times. Therefore, dense small cell deployment is the only efficient way to support 1000 time more capacity in 5G network [30]. This dense nature of the small cell grid will present the following challenges for 5G backhaul:
Denser backhaul link due to the denser small cell grid will highly limit the frequency reuse, which will require better utilization of wireless backhaul spectrum [30].
There will be some set to unprecedented requirements for cell site synchronization. According to the forecast, 5G network will need three times stricter accuracy requirements than LTE-A (i.e., 1.5 μs to approx. 0.5 μs) [17].
Small cell backhaul requirements (e.g., traffic load intensity, latency, target quality of service, and cost of implementing backhaul connections) can vary significantly depending on the locations of the small cells [24]. Besides, the available backhaul scenarios can greatly vary, for example, some places fiber connection may be available but it may not be available for other places. Some places may be good line of sight microwave connectivity but it may not be available for every places. So, there is no single technology that can dominate backhaul technology [25]. There are many options, and the operators have to decide which backhaul solution will be most economical for any particular deployment scenarios. This section describes available backhaul solution that can be used for 5G networks.
\nA compressive study of wired backhaul solution is presented in [16]. So this subsection describes the fiber backhaul connection only. Fiber is the most popular backhaul solution that can provides highest capacity with low bit error rate and it allowed highest reach before any signal needs to be retransmitted. That’s why fiber is always remains as the first choice for backhaul if it is available. Unfortunately, fiber is not available for most of the places. For example, one study conducted in 2014 present a fact that the fiber backhaul is not available nationwide in Europe and the alternative microwave backhaul solution will not sustain the traffic growth of LTE/LTE-A beyond 2017–2018 [16]. There are some other instances as well, such as nearby backbone fiber does not exist and there is no right of way available, or there are some obstructions (e.g., highways or rivers or buildings) that will make the fiber connection impossible. In addition, the deployment of new fiber connection will take several months compared with wireless deployments that can be completed within a week. Initial deployment cost of fiber connection is also high that includes cable costs, splicing, trenching, right of way, etc., plus the cost of equipment’s for the optical transport and aggregation [23]. So, it is obvious that the fiber connection will be first choice for backhaul if it is available otherwise we have to look for other backhaul solution that meets the requirements of 5G networks.
\nSupport the backhaul traffic from radio switch to cell site wirelessly (i.e., wireless backhaul) becomes popular due to the viability, and cost-efficiency. Wireless backhaul (e.g., microwave, millimeter wave) allows operator to have end-to-end control of their network instead of leasing third party wired backhaul (e.g., fiber) connections. However, the optimal selection among wireless backhaul solution depends on several factors that includes cell site location, propagation environment, desired traffic volume, interference conditions, cost efficiency, energy efficiency, hardware requirements, and the availability of spectrum [24]. This subsection describes the available wireless backhaul solution that can be used for small cell backhaul in 5G networks.
\nWireless backhaul technology supports approximately 50% of mobile traffic globally where, microwave RF technology has the vast majority [23]. It typically operates in the 6, 11, 18, 23, and 28 GHz frequency bands. The deployment of microwave radio requires one-time capital cost and there is some other costs that includes space/power rental and maintenance. So, microwave RF can be deployed at a much lower cost and the deployment time is much faster compared to fiber connection. However, the performance of microwave RF backhaul solution significantly varies with the propagation environment and bad weather condition. Often the system need to lower the transmission rate to maintain the availability requirements. Typically microwave RF can support up to 500 Mbps capacity and the maximum reach could be 30 miles which may also vary with the applications. For examples, if we use lower frequency band we can achieve longer reach but lower frequency bands are congested and may not be available for backhaul solution. On the other hand, if we use higher frequency we can have higher date rate but the system has to sacrifice the long reach. Microwave RF system capacity can be increased up to 10 Gbps for long and medium distance connectivity by utilizing wider channel spacing (e.g., 112 MHz for traditional microwave bands 4–42 GHz), higher order modulation schemes (e.g., 4096 QAM and up), and the use of ultrahigh spectral-efficiency technique (e.g., line of sight MIMO) [30].
\nAccording to International Telecommunication Union (ITU), millimeter wave operates in Extremely High Frequency (EHF) which is range in 30–300GHz. So the millimeter wave RF can become prominent for small cell backhaul solution due its enormous spectrum [32]. Besides, smaller wavelengths will enable the integration of large number of antennas in a simple configuration and small cell can take this advantage of massive MIMO for LOS or non-LOS backhaul solutions. Typically, millimeter wave RF can support high data rate up to 1–2 Gbps range but the reach is shorter compared to Microwave RF due to the high propagation loss at millimeter wave [16]. The major factor that causes propagation loss includes, absorption, rain fading, and multipath propagation. Typically, the millimeter wave beams are much narrower compared to microwave beams that creates a major constraint which is line of sight (LOS) backhaul solution. Narrow beam can also create alignment problem and to avoid this problem, millimeter wave RF equipment’s need to be installed in a solid structure [23].
\nFree space optics (FSO) is a line of sight backhaul technology which is similar as fiber optics except FSO uses invisible beam of light (e.g., LED, LASR) for data transmission instead fiber cable [33, 34]. FSO has enormous spectrum in the range of 300 GHz to 1 THz and the maximum data rate can support up to 10 Gbps (both upstream and downstream) [16]. The major advantage of FSO is low power consumption compared to microwave or millimeter wave RF. But FSO system has number of constraints that includes LOS communication, fading due to fog, interference due to ambient light, scattering and physical obstructions. However, FSO technology can be one of the possible solution for 5G backhaul due to its scalability and flexibility [33].
\nAlthough there are some other wireless backhaul solutions (e.g., Satellite and TV White Spaces (TVWS)), but maximum data rate can support is less than 1Gbps and the latency requirement is also high. This is the main reason not to add much details about this two backhaul technologies. The available features (e.g., latency, reach, and throughput) of all wireless backhaul technologies are summarized in Table 2.
\nTechnology | \nDeployment cost | \nLatency | \nReach | \nUpstream throughput | \nDownstream throughput | \nOptions | \n
---|---|---|---|---|---|---|
Satellite | \nHigh | \n300 ms one-way latency | \n∼Ubiquitous | \n15 Mbps | \n50 Mbps | \nLOS | \n
TVWS | \nMedium | \n10 ms | \n1–5 km | \n18 Mbps/ch | \n18 Mbps/ch | \nNLOS | \n
Microwave PtP | \nMedium | \n<1 ms/hop | \n2–4 km | \n1 Gbps | \n1 Gbps | \nPtP | \n
Microwave PtmP | \nMedium | \n<1 ms/hop | \n2–4 km | \n1 Gbps | \n1 Gbps | \nPtmP | \n
Sub-6 GHz 800 MHz–6 GHz | \nMedium | \n5 ms single-hop one way | \n1.5–2.5 km urban, 10 km rural | \n170 Mbps | \n170 Mbps | \nNLOS | \n
Sub-6 GHz 2.4, 3.5, 5 GHz | \nMedium | \n2–20 ms | \n250 m | \n150–450 Mbps | \n150–450 Mbps | \nNLOS | \n
MmWave 60 GHz | \nMedium | \n200 μs | \n1 km | \n1 Gbps | \n1 Gbps | \nLOS | \n
MmWave 70–80 GHz | \nMedium | \n65–350 μs | \n3 km | \n10 Gbps | \n10 Gbps | \nLOS | \n
FSO | \nLow | \nLow | \n1–3 km | \n10 Gbps | \n10 Gbps | \nLOS | \n
As it is seen from Table 2, FSO provides highest throughput with lowest latency which is the basic requirements of 5G backhaul. This is the main motivation of this paper where FSO is used for 5G backhaul networks with addition of ambient light cancelation technique at the receiver, described in Section 4.
\nAccording to the use cases, services, and network requirements of 5G, the next generation mobile network will not only human centric. This network will allow to connect new type of devices that support machine-to-machine (M2M) services and Internet of Things (IoT). Therefore, the backhaul network must meet diverse network requirements based on the type of user traffic, such as, some user traffic may care more about the maximum network speed not latency and on the contrary the users may care about the low latency not the speed. So, it is obvious that there will be no unique backhaul solution for 5G networks. Based on the deployment area and user traffic, the 5G backhaul network will be a combination of wired (e.g., fiber) and wireless backhaul (millimeter wave, and free space optics). Thus, understanding the basic backhaul network requirements is the key to choose the right technology and type of network. In an effort, this book chapter first introduce the backhaul network perspective for 2G, 3G, and 4G networks and then outlines the backhaul requirements of 5G networks. This chapter also describes the available backhaul solutions and describes the key challenges.
\nThe field of plasmonics has advanced immensely over the years and is spreading more and more into the area of sensor technology [1, 2, 3, 4]. This is due to the unique interaction of light with noble metals [5]. The excitation of conduction electrons to perform collective vibrations, both in volume as well as at the surface, shows in brilliant colors, which have fascinated people since the medieval times. Countless prominent examples of art objects still exist today, such as the Lycurgus Cup (4th century AD) and stained-glass windows of cathedrals.
As early as 1857, Michael Faraday published his groundbreaking findings (The Bakerian Lecture of the Royal Society of London [6]) on the experimental interactions of gold and other metals with light [7]. “Light has a relation to the matter which it meets with in its course, and is affected by it, being reflected, deflected, transmitted, refracted, absorbed, etc. by particles very minute in their dimensions [6].” He studied the emergence of different colors for fluids containing gold reduced to diffused particles and described the metallic character of the divided gold: “Hitherto it may seem that I have assumed the various preparations of gold, whether ruby, green, violet, or blue in color, to consist of that substance in a metallic divided state [6].”
Between 1900 and 1920, the famous contributions of James Clerk Maxwell Garnett [8], Gustav Mie [9], Richard Gans [10, 11], and Richard Adolf Zsigmondy [12], just to name a few, proved that plasmonic colors were based on optical resonances that occur for particles smaller than the wavelength of light and that can be theoretically described and precisely predicted [13, 14, 15]. This birthed the field of colloidal plasmonic nanoscience [16]. During the last few decades, a variety of different nanostructures, both in the form of individual NPs and particle assemblies [17], have been developed with a special focus on their use as colorimetric or SERS spectroscopy sensors [18, 19].
Today’s pronounced diversity of available nanostructures demonstrates the high level of interest in these optically functional materials. Within the scope of this book chapter, this diversity can, of course, only be covered to a limited extent. For this reason, the focus here is on NPs as defined building blocks for discrete nanostructures by guided self-assembly [20, 21, 22]. Figure 1 provides a rough overview of functional structures which have been found to be particularly suitable for sensor applications. The first area is represented by individual nanocrystals, for example, in spherical, rod-shaped, triangular, or star-shaped morphologies with strong intrinsic electromagnetic hot spots. This can be extended by coupling these particles to a metal surface or thin-film, the formation of branched structures by overgrowth, or hollow, core/shell, and nested structures with nanoscale interior gaps. Nanoparticles at short distances form extrinsic hot spots by strong electromagnetic interactions [23], referred to as plasmonic coupling [24]. Even in the disordered state, particle aggregates produce strong field enhancements. However, it is the ordered assembly of particles that allows plasmonic hybridization to emerge [25]. Hybridization can result in highly sensitive modes for spectral shift sensing and intense near-field enhancement for chemical sensing [14]. Again, the diversity ranges from discrete single nanoclusters with uniform coordination numbers to complex superstructures, supercrystals, and patterned structures both in 2D and 3D, which can be fabricated by colloidal engineering.
Schematic overview of the diversity in plasmonic nanoparticles and -structures: (top, left) nanocrystals, film-coupled particles, and hollow/nested morphologies on single particle level; (top, right) disordered assemblies of aggregated NPs; (bottom) ordered assemblies of discrete NP oligomers, clusters, and defined superstructures in 2D and 3D.
In this chapter, we will first address the field of plasmonic colorimetric sensing. Here, the fundamental concepts for sensing of surface plasmon resonances of metallic thin films are reviewed and then extended to localized surface plasmon resonances [26] of NPs and ordered NP assemblies by guided self-assembly [20, 21, 22]. Second, we will review SERS analytics divided into several steps: the first principles of SERS [27] and off-resonance excitation, SERS analytics of dispersed particles with a focus of the tasks of functional shells, SERS analytics using disordered aggregates under controlled conditions, and finally ordered assemblies designed for high SERS activity [28, 29].
To begin, we will first briefly review SPR spectroscopy of thin metallic films as a foundation for LSPR spectroscopy. Colorimetric sensing describes the optical determination of chemical or physicochemical properties of a sample. Subsequently, we will discuss concepts in which the plasmonic response is used to obtain information at interfaces or at the near-field environment of metal structures, which would otherwise be inaccessible.
Surface plasmons (SPs) are electromagnetic waves, emerging from surface plasmon resonances (SPRs), that propagate along the surface or interface of a conductor, usually a metal/dielectric interface [30]. Essentially, surface plasmons are light waves trapped at interfaces because of their strong interaction with the free electrons of the conductor. Surface structuring can guide this interaction [31]. The response of the free electrons takes place collectively in the form of oscillations in resonance with the light wave. The consequent charge density oscillation at the surface leads to a concentration of light and thus an enhancement of the local electric nearfield. The high sensitivity of this light-matter interaction renders it attractive for sensing applications. SP-based sensing builds on a simple resonance condition:
The resonance condition requires the SP mode (with frequency-dependent wave-vector ksp) to be greater than that of a free-space photon of the same frequency (free-space wave-vector k0). In addition, for SPRs, the frequency-dependent permittivity of metal (εm) and dielectric (εd) need to be of opposite signs. As a consequence, the SP resonance phenomenon has been employed for biochemical sensing [32] and clinical diagnosis [33]. Under appropriate conditions, the reflectivity of a thin metal film is extremely sensitive to changes in the local refractive index environment. Figure 2A (left) shows an exemplary SPR sensor in a fluidic channel in Kretschmann configuration using a prism for coupling p-polarized light into the metallic film interface [34]. The resulting evanescently decaying field reaches beyond the metallic interface into the sensing medium. When the SPR condition is satisfied, the reflection spectrum for monochromic light shows a characteristic resonance dip (Figure 2A, right). Here, the resonance condition is
where n denotes the refractive indices of the dielectric prism (p) and the sensing medium (s), λ is the wavelength in free space, and θ is the incident angle of light [34]. Thus, changes of the refractive index (Δn) of the sensing medium will shift the resonance dip by altering the resonance angle (Δθ) and/or the resonance wavelength (Δλ). The sensing of this resonant spectral response can be realized in different micro- and nanostructured sensor configurations (e.g., prism-, waveguide-, channel-, grating-based setups) [35]. Oates et al. demonstrated that the established methods of SPR spectroscopy for chemical and biological sensing can be enhanced by using the ellipsometric phase information [31]. Next, we focus on colorimetric sensing using plasmonic NPs.
Fundamental concepts of colorimetric plasmonic sensing. (A) SPR sensor in a fluidic channel. Copyright 2011 MDPI, adapted with permission [34]. (B) Pregnancy test using AuNPs as inert dye. (C) Refractive index sensitivity of an AgNP-based optical sensor. Copyright 2003 ACS, adapted with permission [44]. (D) LSPR sensor concept for enzyme-guided inverse sensitivity [45]. (E) Dual-responsive hydrogel/AuNP hybrid particles. Copyright 2016 NPG, adapted with permission [47]. (F) Protease-triggered dispersion of AuNP assemblies. Copyright 2007 ACS, adapted with permission [48].
The transition from SPR to localized surface plasmon resonance (LSPR) sensing is accompanied by the step from sensors using metallic thin-films to nanosensors in the form of particulate matter [36, 37, 38]. The plasmon generated on a small nanoparticle, for example, a sphere, experiences strong spatial confinement because of its hindered and limited propagation [39]. This confinement, also known as localization, results in discrete charge density oscillations [9, 40], which manifest themselves by intensive colors [41]. The excitation frequency of localized plasmons (absorbance band) is highly sensitive for the size, shape, composition, and refractive index environment of the NP. Though LSPRs were capitalized for various nanophotonic applications covering many fields [16, 26, 42], this chapter is limited to their use as sensor elements. For this purpose, we briefly survey the most commonly used and prominent concepts for colorimetric sensing.
Figure 2 summarizes the fundamental colorimetric sensing concepts using single NPs and disordered NP assemblies. The first example shows the working principle of a pregnancy test for which AuNPs (conjugated to anti-hCG antibodies, blue) serve as an inert dye to detect the presence of hCG antigens (green, Figure 2B) [43]. The test is basically a lateral flow sandwich immunoassay consisting of a test line with anti-hCG antibodies (violet), a control line with immunoglobulin G (IgG, red) antibodies, and a mixing with immobilized anti hCG-conjugated AuNPs. By application of a urine sample, the NPs bind to available hCG antigens (which are indicative for a pregnancy). This is followed by the selective binding of AuNPs to the control and test line, while the latter only happens in the presence of hCG antibodies. In this example, the AuNPs serve as an inert dye which does not interfere with the antibody–antigen binding by biorecognition and possesses high chemical stability.
Figure 2C highlights the refractive index sensitivity of an AgNP-based optical sensor in various solvent environments (left) [44]. Van Duyne et al. found a linear relationship between the refractive index environment and the LSPR position. This enabled to detect the adsorption of fewer than 60,000 1-hexadecanethiol molecules on single AgNPs which corresponded to a 41 nm shift followed by dark-field spectroscopy. However, for ultralow concentrations, the variations in the physical property (e.g., LSPR shift) become increasingly smaller, and thus, harder to detect with confidence. Contrary to conventional transducers which generate a signal that is directly proportional to the concentration of the target molecule, Stevens and coworkers proposed an LSPR sensor with inverse sensitivity (Figure 2D) [45]. The key for this inverse sensitivity is the enzymatic control over the rate of nucleation of Ag on Au nanostars (top: overgrowth; bottom: nucleation), accompanied by a blueshift of the LSPR. Different biosensing strategies have been proposed building on enzymatic reactions and NPs [46].
Apart from dispersed NPs, the plasmonic coupling between NPs, which is dependent on their spatial interspacings, can be utilized for colorimetry. Song and Cho reported dual-responsive architectures by mixing hydrogel and AuNP-decorated hydrogel particles (Figure 2E) [47]. This hybrid ensemble responds to both temperature and ions by means of a volume and color change in aqueous systems. Both stimuli can be used to reversibly trigger the transition of uncoupled well-separated AuNPs (red tint) to a state that allows for plasmonic coupling (blue tint), mediated by the hydrogel matrix. Ulijn and Stevens et al. demonstrated the bioresponsive transition from aggregated to dispersed state [48]. Figure 2F shows the protease-triggered dispersion of AuNP assemblies using thermolysin for the removal of attractive self-assembly groups and revelation of repulsive charged groups. The consequent blueshift of the LSPR allowed for simple and highly sensitive detection of the presence of thermolysin, which could be tailored for different proteases.
Another approach builds on measuring the orientation of a sample. For this, it is necessary to align the ensemble of NPs macroscopically. This was achieved for anisotropic NPs homogenously dispersed in an elastic polymer matrix [49, 50]. By uniaxial stretching of the material, the NPs are oriented along the direction of elongation. As a result, the material exhibits uniform plasmonic response, which enables for optical detection of the orientation of the material. Continuing on, we will examine assemblies containing ordered NPs and patterns.
Figure 3 highlights colorimetric sensing examples of ordered NP assemblies and defined patterned superstructures. Because the LSPR depends on the local dielectric environment at the NP surface, the LSPR shift can be evaluated to detect changes in effective refractive index. The first example is a macroscopic plasmonic library consisting of well-separated non-coupling AuNPs with a gradient in size, induced by Au overgrowth [51]. Along the array, the size increase goes along with a color change from colorless to pink (Figure 3A, left). Aided by electromagnetic simulations, it was possible to evaluate the effective refractive index and thus changes in the local density of the hydrogel shell around the substrate-supported particles (right). The initial increase of the refractive index indicated a densification of the hydrogel network upon particle growth from 10 to 30 nm. The subsequent decrease above 30 nm might result from internal breakup/rupture of the network.
Colorimetric sensing concepts of ordered NP assemblies and defined patterned superstructures: (A) Effective refractive index of a substrate-supported array of particles with a gradient in sizes. Copyright 2014 ACS, adapted with permission [51]. (B) Core/satellite assemblies for highly sensitive refractive index sensing. Copyright 2015 ACS, adapted with permission [52]. (C) Biomolecular detection by disassembly of core/satellite assemblies. Copyright 2011 ACS, adapted with permission [54]. (D) Stress memory sensor based on disassembly of AuNP chains. Copyright 2014 ACS, adapted with permission [56]. (E) Mechanochromic strain sensor based on AuNP-decorated microparticles dispersed in a polymer matrix. Copyright 2017 Wiley, adapted with permission [59]. (F) Reversible strain-induced fragmentation of quasi-infinite linear assemblies to defined plasmonic oligomers. Copyright 2017 ACS, adapted with permission [62].
Sönnichsen et al. proposed the use of core/satellite assemblies for highly sensitive refractive index sensing [52]. Figure 3B (left) shows 60 nm AuNPs as cores linked to 20 nm AuNPs as satellites. The average number of satellites allowed tuning the LSPR from 543 to 575 nm. The core/satellite nanostructures showed about twofold higher colorimetric sensitivity (Δλ/Δn) than similar sized gold NPs (right). Lee et al. developed a theory-based design of such core/satellite assemblies to optimize the spectral shift due to satellite attachment or release. They provided clear strategies for improving the sensitivity and signal-to-noise ratio for molecular detection, enabling simple colorimetric assays [53]. Figure 3C depicts the disassembly of substrate-supported core/satellite assemblies for biomolecular detection [54]. By addition of trypsin, the cysteine/biotin-streptavidin peptide tethers were proteolytically cleaved to release the satellites into solution enabling colorimetric detection of the protease.
Different concepts have been developed for opto-mechanic sensitivity and control [55]. Yin et al. reported a stress-responsive colorimetric film that can memorize the stress it has experienced (Figure 3D, left) [56]. This stress memory sensor is based on the LSPR shift associated with the disassembly of chains of AuNPs embedded in a polymer matrix (middle). By plastic deformation, the LSPR experiences a blueshift by irreversible breaking of the linear AuNP assemblies, initially formed in colloidal suspension [57]. The sensitivity of the optical change to stress could be tuned by doping with different amounts of PEG as plasticizer (right) [56]. Instead of mixing NPs with an elastic matrix, AuNPs can also be grown at the surface of a flexible substrate [58]. This enables mechanical control of the plasmonic coupling and electromagnetic fields at the surface. Dreyfus and coworkers designed mechanochromic AuNP-decorated microparticles as strain sensor (Figure 3E) [59]. After dispersion in an elastic polymer matrix of PVA, the capsules change in color upon elongation. When the film is stretched, the capsules are deformed into elongated ellipsoidal shapes and the distance between the AuNPs, embedded in their shells, concomitantly increases. Another mechanoplasmonic approach has been proposed for substrate-supported chains of AuNPs. Figure 3F (left) shows oriented linear assemblies, above the so-called infinite chain limit [60, 61], in a periodic pattern over cm2 areas on an elastic support [62]. Upon external strain, the assemblies experience a transition from long to short chains by reversible strain-induced fragmentation. The transition from plasmonic polymers to oligomers was accompanied by a pronounced spectral shift (right). A similar strain sensing approach was reported by Minati and coworkers using 1D arrays of broader line widths [63]. These multiparticle arrays showed a blueshift of the reflectance, lineally scaling with the external strain. Here, we will leave the field of colorimetric sensing and turn our attention to the enhancement of the electric field and the concomitant SERS activity.
Since its discovery by Martin Fleischmann, Patrick J. Hendra, and A. James McQuillan in 1974, surface-enhanced Raman scattering has become an indispensable tool for analytical chemistry [64]. In this study, two types of pyridine adsorptions have been identified at Ag electrodes [65]. At the same time, the detected signal strengths were far beyond what could be expected to arise from local concentration of absorbed molecules. In 1977, two enhancement theories were proposed independently, namely chemical enhancement [66] by Albrecht and Creighton and electromagnetic enhancement [67] by Jeanmaire and Van Duyne. Here, we will limit our discussion on the electromagnetic theory, because it is most closely linked to the optical and structural properties of nanocrystals and their assemblies. After an initial review of the origin of SERS enhancement [68, 69], we will go over prominent examples for the application of SERS for chemical spectroscopy.
The Raman process describes the inelastic scattering of light by atoms or molecules discovered by C. V. Raman in 1928 [70]. This process had already been proposed theoretically by Adolf Smekal in 1923 [71]. In principle, Raman scattering builds on the interaction of a photon and a molecule (or crystal) for which an energy transfer can occur (Figure 4A) [72]. However, the Raman process has an inherently low cross-section because the probability of this transfer is very low and only 1 in 107 photons are scattered inelastically. For that reason, long measurement times are necessary to compensate for the low photon yield. Therefore, the low time resolution and the limitation of the spatial resolution demand on excellent optics. The SERS effect dramatically improves the photon yield, overcoming these limitations. To clarify this, it is necessary to look at the origin of the enhancement [68].
First principles of surface-enhanced Raman scattering: (A) schematic of the two-photon non-resonant stokes scattering between two vibrational states of a molecule (n = 0 - > n = 1) mediated by a virtual state v. A harmonic potential (solid line) approximates the energy landscape of the ground electronic level (dashed line). Copyright 2016 ACS, adapted with permission [72]. (B) Schematic of the twofold amplification process. (C) Single-molecule spectra of rhodamine Rh123 of AgNP aggregates (solid lines) reflecting the approximate shape of their corresponding Rayleigh scattering spectra (dotted lines). Copyright 2007 APS, adapted with permission [79]. (D) Comparison of individual single-molecule events to average signal (7500 spectra). Copyright 2010 ACS, adapted with permission [75]. (E) Electric field confinement of nanosphere, nanorod, nanotriangle, and core/satellite nanocluster; scaled to maximum visibility. Copyright 2016 ACS, adapted with permission [77]. (F) Selective excitation and spatial transfer of hot spots in dimer gap, in both junctions, or only in the particle−film junctions. Copyright 2016 ACS, adapted with permission [78].
Raman scattering is, in its most basic and phenomenological form, the emission of a molecular Raman dipole (λsca = λexc ± Δλ) [27]. Induced by the electric field Eexc of the exciting laser light λexc, a Raman dipole p0 oscillates at a Raman-shifted frequency (ωsca = 2πc/λsca).
For a randomly oriented Raman scatterer, the radiated power is proportional to |p0|2 [68]. Thus, in order to enhance the Raman signal either the polarizability α or the electric field E need to be magnified. The former refers to chemical enhancement, this is the modification of the local polarizability of the molecule (α0 -> αloc), whereas the latter is called electromagnetic enhancement EM and describes the augmentation and confinement of the local near-field (E0 -> Eloc). The enhanced dipole p can be written as
The dipole enhancement upon excitation can be expressed by
Likewise, the dipole enhancement upon emission, that is, the Raman scattering, is given by
Although it is convenient from a theoretical point of view to separate the excitation and scattering into two steps, the Raman scattering process is instantaneous and both occur simultaneously [27]. The combined enhancement MSERS contains both contributions of the twofold amplification process (Figure 4B) [73]: the augmented excitation of a molecular dipole by an incident photon (λexc) and the stimulated emission of a scattered photon (λsca) of higher (anti-Stokes, λsca < λexc) or lower energy (Stokes, λsca > λexc).
Often, the total enhancement is simplified by the so-called |E|4-approximation, which neglects the Raman shift. However, this approximation needs to be treated with caution as many cases have shown [74].
The questions of why and how the shapes of SERS spectra change has been addressed by Yamamoto and Itoh [73]. The transformation of the Raman spectrum, in principle the Raman cross section σRS, by the SERS process can be described as follows:
If Eq. 9 holds true, this would enable the reconstruction of a SERS spectrum from the unenhanced Raman spectrum and an enhancement function MSERS(λ). Yamamoto and Itoh proposed that this reconstruction might be given by the product of the Raman spectrum times the Rayleigh scattering spectrum, based on observations using AgNP nanoaggregates (Figure 4C) [73]. They found that single-molecule spectra of rhodamine Rh123 (solid lines) were well reflecting the approximate shape of their corresponding Rayleigh scattering spectra (dotted lines) both for Stokes as well as Anti-Stokes scattering [43, 47]. Figure 4D shows a comparison of individual single-molecule events to average signal (7500 spectra) for Nile blue measured with Ag aggregates at high spectral resolution [75]. The ensemble averaging of many events revealed the characteristic broadening of the average spectrum (top) and fitted to Lorentzian line shapes (bottom).
All the reviewed examples, up to now, have capitalized from aggregated Ag nanocolloids as, for example, introduced by Lee and Meisel [76]. Such disordered aggregates enabled breakthrough results in regard to pushing the limit for ultrasensitive detection, down to single-molecule resolution, as well as nurtured the fundamental understanding of the origin of SERS enhancement. In the following section, we will turn our attention from disordered aggregated systems to individual nanocrystals and their ordered assemblies. The main aim is to find appropriate criteria for the design of nanostructures with both high and robust enhancement.
As a first step, we address the formation of hot spots, so-called confined locations with the highest electric field strengths. For individual nanoparticles, hot spots can be found at the poles of nanospheres (e.g., in respect to an excited dipolar mode, see Figure 4E, left) or near areas of high surface curvatures, as at the tips of nanorods and nanotriangles (middle). In multiparticle systems, hot spots form inside interparticle gaps, cavities, or crevices, as depicted for an exemplary core/satellite assembly (right) [77]. Depending on the nature of the excited LSPR modes and considering plasmonic hybridization in multiparticle systems, the distribution of hot spots can be quite diverse. For instance, the lighting of special hot spots has been demonstrated for film-coupled multiparticle configurations [78]. Figure 4F shows the basic example for selective excitation and spatial transfer of hot spots in a AuNP dimer. Depending on the excitation wavelength, the hot spots can be formed either in the dimer gap, in the particle-film junctions, or in both junctions at the same time [78]. Electromagnetic simulations can give valuable guidance for the design of targeted hot spots in plasmonic nanostructures, especially for complex systems [15, 23].
However, the design of NPs for SERS has shown to be more involved than simply maximizing the local electric field [80]. Murphy et al. initially reported the surprising finding of the highest SERS signals for LSPRs, blue-shifted from the wavelength of laser excitation. They studied an ensemble of Au nanorods of different aspect ratios (but uniform tip curvature) for which the longitudinal LSPRs shifted from 650 nm to 800 nm (Figure 5A, left). Contrary to expectations, the batches with matching of LSPR and laser excitation performed worse than off-resonant batches (right). This has been explained by a competition between SERS enhancement and extinction. The initial assumption that the LSPR is an adequate prediction for the best SERS performance has been shown to be incorrect.
Off-resonance SERS enhancement: Non-linear dependency of (left) optical properties and (right) SERS signal intensities for variably sized (A) nanorods and (B) nanotriangles. (A) Copyright 2013 ACS, adapted with permission [80]. (B) Copyright 2018 ACS, adapted with permission [81].
Further validation was provided by a similar approach, screening the correlation of Au nanotriangle size and SERS performance [81]. Upon overgrowth, the LSPRs showed a continuous shift toward near-infrared (Figure 5B, left). Again, the highest SERS enhancement did not coincide with matching of the LSPR to the laser wavelength. Instead, the highest SERS activity was identified in off-resonance conditions (right). To rule out the influence of possible differences in tip/edge sharpness, the nanotriangle morphology was characterized by a close correlation of electron microscopy (TEM, field-emission SEM) and small-angle X-ray scattering (SAXS) analysis [50, 77, 81] combined with 3D atomistic modeling. This revealed a uniform tip curvature for all sizes.
The assumption that aggregation might be the cause for the off-resonant SERS activity was thoroughly investigated. Optical spectroscopy (UV-vis-NIR) before and after addition of the Raman marker did not show any indication of aggregation. Reversible aggregation/association of particles could be ruled out because of the presence of a sufficient amount of stabilizing agent (CTAB) in the solution. The amount of Raman marker (4MBA) added was much lower than that of the available stabilizing agent (>50-fold molar excess). The marker was not expected to act as a molecular linker. Also, in the case of irreversible aggregation, one would expect a loss of particles over time, which was not observed. The video feedback of the Raman microscopy did not give any indication of possible formation of aggregates even after the extended laser exposure. The colloidal dispersions were found to exhibit high colloidal stability for the reported surfactant concentrations, and the SERS signals could be detected reproducibly. Thus, even if aggregation (below the detection limit) was present, it would be of negligible contribution and should not have affected the registered SERS spectra [81].
Consequently, in many situations, the hot spot intensity is not directly correlated to the optical properties; thus, the extinction maximum is often not the best excitation wavelength for SERS [81]. As a rule, an increase in SERS activity can be expected for situations in which the Stokes-shifted Raman signals lies in the low-energy shoulder of the LSPR band; in other words, when the laser line is shifted to the red, compared to the LSPR extinction maximum.
At this point, we move to the application of SERS for analytical purposes. The term “single or individual particles” indicates that the NPs are present in a dispersed state in colloidally stable dispersions and that aggregation is avoided. First, examples will be discussed that highlight the retrieval of chemical information at the NP surface. Then, we will address the specific tasks of the different shells and its versatile functions for SERS applications.
SERS analytics have proven to be a valuable tool for the detection, studies of the exchange and competitive adsorption, as well as localized chemical reactions of ligands at NP surfaces in dispersion.
Hafner et al. applied SERS analytics to study the structural transition in the surfactant layer that surrounds Au nanorods (Figure 6A, left) [82]. This was achieved by following the displacement of surfactant by thiolated poly(ethylene glycol). At the same time, they characterized the surfactant bilayer, revealing the absorbed layer of counterions at the gold surface Au+X−, the ammonium head group CN+, and the skeletal vibrations of the alkane chain of the surfactant (right). Building on these findings, Chanana et al. investigated the quantitative exchange of surfactant against protein (bovine serum albumin) on Au nanorods (Figure 6B, left) [83]. In the context of biotoxicity, the cationic surfactant (CTA+X−) needs to be removed from the solution and NP surface. This required analyzing the broad spectral range from 100 to 3100 cm−1, covering all the characteristic signals associated with the ligand exchange (right). This evidenced the complete surfactant removal, which is a key step toward safe bioapplication of protein-coated NPs.
Detection, exchange, competition, and chemical reaction of ligands by SERS analytics in dispersion: (A) surfactant bilayer characterization on au nanorods (counter ion au+X−, ammonium head group CN+). Copyright 2011 ACS, adapted with permission [82]. (B) Quantitative exchange of surfactant against protein on au nanorods. Copyright 2015 ACS, adapted with permission [83]. (C) Competition of aromatic surfactants (BDA+), non-aromatic surfactants (CTA+), and thiol ligands (4MBA) on au nanotriangles. Copyright 2018 ACS, adapted with permission [81]. (D) Hot electron-induced reduction of small ligands (NTP to ATP) on Ag core/satellite assemblies. Copyright 2015 NPG, adapted with permission [85].
The competition of aromatic surfactants (BDA+), non-aromatic surfactants (CTA+), and thiol ligands (4MBA) was studied on Au nanotriangles (Figure 6C) [81]. Contrary to expectations, first evidence for the nonquantitative nature of the ligand exchange of aromatic versus non-aromatic surfactants was found. Differences in binding affinity toward the NP surface are attributed to additional π-interactions of the electron-rich benzyl headgroup [84]. It was possible to detect a trace amount of BDA+ of 1–10 nM, which originated from the seed synthesis and could not be removed even after excessive washing with CTAB surfactant [81].
Schlücker and Xie applied SERS analytics to follow nano-localized chemistry on Ag core/satellite assemblies (Figure 6D, left) [85]. They reported the hot electron-induced reduction of small ligands (NTP to ATP) in the absence of chemical reduction agents. The reduction was shown to be dependent on the available halide counterions X− (middle, right).
The shell can provide for different functionalities, such as inertness, hosting of Raman markers, molecular trapping, harvesting/accumulation of analyte molecules, but also by means of improving the SERS activity.
The first examples represent chemically inert shells to protect SERS-active nanostructures from contact with whatever is being probed. This concept has been introduced by Tian et al. and entitled as shell-isolated NP-enhanced Raman spectroscopy (SHINERS) [86]. The silica shell acts as a nanoscale dielectric spacer. Such particles have been applied for the in-situ detection of pesticide contaminations on food/fruit [87]. Silica encapsulation can also be used to protect a molecular codification, a layer of Raman markers at the NP surface (Figure 7A) [88]. A silica shell enables further functionalization, chemical post-modification, and assembly of superstructures [89]. At the same time, silica overgrowth can stabilize superstructures as well as increase their colloidal stability and robustness (Figure 7A).
Functional shells for augmented SERS applications of single nanoparticles: (A) silica coating of dispersed AuNPs and overcoating of core/satellite superstructures. Copyright 2011 Wiley, adapted with permission [88]. (B) SERS-encoded NPs enclosed in silica. Copyright 2015 ACS, adapted with permission [90]. (C) Hydrogel-encapsulation for thermo-responsive molecular trapping. Copyright 2008 Wiley, adapted with permission [93]. (D) Branched morphologies grown inside radial mesoporous silica shells. Copyright 2015 ACS, adapted with permission [94]. (E) Schematic core/shell particle with nanoscale interior gaps and nanobridges [95]. (F) Interior nanogap within double-shelled au/Ag nanoboxes. Copyright 2015 NPG, adapted with permission [96]. (G) Protective au overcoating of AgNPs to increase their chemical stability. Copyright 2018 Wiley, adapted with permission [99].
Pazos-Pérez and Alvarez-Puebla et al. demonstrated the SERS encoding of particles. For this, the NP surface is first partially functionalized by a stabilizing ligand, followed by a codification with a SERS marker (Figure 7B), and the final overcoating with silica to create an inert outer surface layer [90]. Also, hyrogel shells have shown the potential for molecular trapping of analyte molecules [91, 92]. The partial hydrophobic/hydrophilic nature of poly(N-isopropylacrylamide) during the reversible volume-phase transition can harvest analyte molecules from solution. After accumulation, the induced collapse of the shell can serve to increase the local concentration of analytes at the NP surface (Figure 7C, right) [93].
The shell can serve as a means to improve the SERS activity of NPs. For example, as a template for the growth of complex NP morphologies. Liz-Marzán et al. developed an approach for the templated growth of branched Au structures inside of mesoporous silica shells (Figure 7D, left) [94]. The formed tips branching out from the cores (spheres, rods, triangles) improve the plasmonic performance (right) while favoring the localization of analyte molecules at highly SERS-active regions. Another example is the formation of nanoscale DNA-tailorable interior gaps in spherical core/shell particles (Figure 7F) [95]. Interestingly, it has been found that the presence of nanobridges between shell and core does not perturb the hot spot formation. In Figure 7G, this concept is adopted for cubic NPs [96]. For such shelled Au/Ag nanoboxes and nanorattles, a pronounced electric field confinement was found in the interior nanocavity [50].
Metal overgrowth can increase surface roughness by forming bumpy structures [97] or undulated surfaces [98], which both showed increased SERS activity. At the same time, metal overgrowth can increase the chemical stability of NPs. A sub-skin depth Au layer has been shown to enable oxidant stability and functionality without altering the optical properties of Ag nanocubes (Figure 7G) [99].
The field of particle assemblies is sophisticated and versatile. Here, we start with disordered aggregates and then progressively move from small discrete oligomers to large organized multiparticle assemblies in dispersion or supported on substrates. The examples shown are by no means to be considered universally valid but should serve as guidelines for a rational design of assemblies for SERS.
In this section, we briefly delve back into the field of disordered aggregates to explore to what extent these can be formed under controlled conditions for SERS analytics. As introduced in Section 3.1, aggregates can exhibit high SERS activities but suffer from problems concerning reproducibility and robustness. Several approaches addressed these issues and proposed conditions under which aggregation can be induced in a controllable manner.
Gucciardi et al. reported the aggregation of Au nanorods mediated by optical forces and plasmonic heating (Figure 8A) for SERS detection of biomolecules at physiological pH [100]. The formed disordered NP clusters can embed molecules from solution, even in buffered media at neutral pH. The dynamics of the signal increase during aggregate formation have been studied revealing different states (Figure 8B: onset, stabilization, size increase, and saturation). The laser scattering and bright field images showed that such aggregates can reach micron-scale dimensions after extended laser irradiation (over several tens of minutes). Aggregation can also be induced by specific binding, for example, glyco-conjugation of galectin-9 and glycan-decorated AuNPs. The real-time dynamic SERS sensing of galectin-9 in binding buffer, mimicking neutral conditions, revealed three different aggregation ranges, namely an early fast cluster growth, followed by a slower aggregation, before ultimately reaching the final equilibrium state [101]. Similarly, Mahajan et al. employed the selective guest sequestration of cucurbit[n]uril (CB[n]) molecules for molecular-recognition-based SERS assays (Figure 8C) [102]. These macrocyclic host molecules feature sub-nanometer dimensions capable of binding AuNPs. The aggregation produces clusters with a defined interparticle spacing of 0.9 nm. The entitled “host-guest SERS” builds on the capturing of analyte guest molecules inside the barrel-shaped geometry of CB[n] host molecules [102, 103].
SERS sensing based on the formation of disordered aggregates under controlled conditions: (A) laser-induced aggregation by plasmonic heating and (B) aggregation dynamics. Copyright 2016 NPG, adapted with permission [100]. (C) Molecular-recognition-based SERS assay by selective guest sequestration. Copyright 2011 ACS, adapted with permission [102]. (D) Droplet-based microfluidic setup for lab-on-a-chip SERS measurements. Copyright 2016 ACS, adapted with permission [104].
Lab-on-a-chip (LOC) SERS is an approach that is particularly well-suited for diagnostic applications. Figure 8D depicts a droplet-based microfluidic setup for LOC SERS measurements [104]. For measurements, equal amounts of Ag colloids and buffer/analyte solutions were mixed and, finally, 1 M KCl was added for inducing the aggregation in a controlled and reproducible manner [105]. Such microfluidic devices with a liquid/liquid segmented flow, where analyte-containing droplets are formed in a carrier liquid e.g. oil, show great potential for bioanalytics because minimal sample amounts are required and only short analysis times are needed, leading to significant cost reduction [106, 107, 108].
The ultimate goal is to obtain full control over the organization of NPs into discrete clusters. In other words, finding appropriate conditions under which the local association of particles proceeds in a controlled way. This would give access to uniform and discrete assemblies of defined coordination numbers both in 2D and 3D.
The first step toward this goal was achieved by efficient fractionation of 3D clusters by density gradient separation. After purification, the mixed ensemble of clusters was separated yielding pure cluster populations (Figure 9A) [109]. The obtained fractions of monomers (single NPs), dimers, trimers, tetramers, pentamers, and higher species were characterized for their optical properties as well as their capabilities for SERS. The SERS activity per assembly was found to depend on the coordination number, which determines the number of available gaps in a cluster, but also the respective contribution of each gap.
Ordered assemblies designed for high SERS activity. (A) Nanoparticle clusters of discrete coordination numbers. Copyright 2012 Wiley, adapted with permission [109]. (B) DNA-directed 2D core/satellite structures. Copyright 2012 Wiley, adapted with permission [110]. (C) Monolayer of close-packed nanotriangles. Copyright 2017 ACS, adapted with permission [118]. (D) AgNP-decorated silica microparticles. Copyright 2015 ACS, adapted with permission [119]. (E) Patterned supercrystal array of close-packed vertically aligned nanorods. Copyright 2012 Wiley, adapted with permission [124]. (F) Supercrystals of NPs ranging from the nano- to the microscale. Copyright 2012 ACS, adapted with permission [121]. (G) Pattern of pyramidal supercrystal architectures. Copyright 2017 ACS, adapted with permission [126]. (H) Macroscale patterns of quasi-infinite linear NP arrangements. Copyright 2014 ACS, adapted with permission [61].
For the case of substrate-supported “flat” clusters, Bach and coworkers fabricated core/satellite structures using DNA ligands to direct the self-assembly (Figure 9B) [110]. Such “nanoflower”-like 2D structures have shown improved SERS activity as compared to commercial SERS substrates. However, the critical parameter is the size ratio of core to satellite as it controls the coupling strength and plasmonic hybridization. For a high mismatch is sizes, this is for satellites of much smaller size than the core NP, the orbit of NPs is effectively uncoupled from the central NP. But the possible sensing applications of such structures go beyond the formation of hot spots for SERS. For matching building block sizes, Fano-like resonances have been predicted and experimentally observed for structures prepared by e-beam lithography [111, 112, 113]. Such resonances show the characteristic signature in the form of two LSPR peaks separated by a transparency window, a dip in extinction.
Building on this, one might ask what happens if such core/satellite patterns are formed on a curved surface, such as a microparticle, or if the substrate consists of different metallic layers. The latter results in a complex architecture of multilayered core/satellite assemblies surrounding Au/Ag rattles as cores [114]. The rattles exhibit intrinsic hot spots inside the interior cavity between the central rod-like Au core and the frame of Au/Ag alloy [50, 115, 116]. By adsorption of small NPs at the exterior, the LSPR band broadened and shifted further toward red and additional extrinsic hot spots were formed. This broadening was found to be controlled by the density of the satellite particles.
In general, the density of assemblies is a critical parameter for SERS activity. The interparticle distances determine the coupling strength. Here, the coupling threshold of the smallest, in other words, weakest coupling partner limits the interaction strength [117]. For a nanofilm, that is, a dense layer of close-packed particles, this limitation is overcome aided by collective long-range modes. For instance, a layer of nanotriangles prepared by film-casting and solvent evaporation shows nicely arranged edge-to-edge and tip-to-tip ordered arrangements in the monolayer (Figure 9C) [118]. The resulting extrinsic hot spots have been shown allowance for hot electron-driven catalytic reactions such as the dimerization of 4-NTP to 4,4′-dimercaptoazobenzene (DMAB), followed by SERS spectroscopy in a dry state. Radziuk and Möhwald reported close-packed nanofilms of 30-nm sized AgNPs on silica microparticles for intracellular SERS (Figure 9D) [119]. The primary (of individual microparticles) and secondary hot spots (between adjacent microparticles) were utilized for chemical imaging of live fibroblasts [120]. These AgNP-decorated microparticles have been compared to AgNPs with a 5 nm silica shell and silica NPs with a 5 nm thin Ag coating.
The nanofilm concept can be extended to thicker layers ultimately yielding supercrystals of close-packed NPs. Figure 9F presents a study in which supercrystals of NPs ranging from nano- to the microscale dimension have been realized [121]. During this transition, the LSPR band of the building blocks becomes increasingly broad because of higher polar modes. The formed superlattices exhibited pronounced interparticle coupling, whereas only the top layer is available for SERS sensing because of a limited penetration depth. However, patterning can also be utilized to discretize the electromagnetic response of the films/crystals. By comparison of different geometries of discrete supercrystals, it was found that patterning can have a deep impact on the surface electric field generation [122].
In addition to size, the shape of the used building block NPs plays an important role. For anisotropic particles such as nanorods, the local organization becomes essential. Organized nanorod supercrystals in lying-down [123] and standing configurations have shown significant contributions of side-to-side interactions between the close-packed NPs [124]. Bach et al. developed a method for directed nanorod assembly to prepare micropatterned substrates of vertically oriented nanorods (Figure 9F).
Finally, we turn our attention toward complex superstructures of organized NPs such as periodical arrays of pyramidal supercrystals. These superstructures accumulate the electric near-field at the apex of the pyramid [125]. The focalization can be expected to strongly depend on the “sharpness” of the pyramid but also on the internal order. Liz-Marzán and coworkers further developed the templated self-assembly to obtain “high quality” pyramids with highly ordered face-centered cubic lattices with one {100} facet oriented parallel to the pyramidal base and the {111} facets corresponding to the four lateral sides (Figure 9G) [126].
Further examples, highlighting the importance of structural order, are linear 1D assemblies with uniform interspaces. Here, lateral offsetting of NPs and inconsistent spacing can perturb the coupling along the chain [62, 127]. Figure 9H presents macroscale patterns of quasi-infinite linear NP arrangements [61]. The strong plasmonic coupling builds on the regular nanoscale spacing. Both single-line and double-line arrays have been shown to provide for uniform enhancement, with higher values for the single-line arrays [128, 129]. Likewise, the use of anisotropic NPs, which is more challenging, causes the LSPRs to shift further toward the red [130].
Ultimately, the challenge in ordered systems is the control of the interparticle spacings because the gap sizes correlate with the achievable field enhancements. Here, the coating of the NPs plays an essential role, as it may act as a guide for the self-assembly while at the same time act as a spacer in the final nanostructure [20].
This chapter gave an overview of plasmonics in the field of sensing. Starting with nanoparticles with specific morphological and optical properties up to the complex arrangements of these into ordered and even hierarchical superstructures, there is much diversity of accessible nanostructures. Despite this diversity, it must be considered that the structure-property relations need to be well understood to design functional materials with tailored properties.
For colorimetric detection, this represents the fabrication of uniform systems with high spectral sensitivity. Changes in particle size, shape, composition, and arrangement can be used for this purpose. This gives access to many possible applications in the field of biosensing, ion/temperature sensing, mechanosensing, to name a few. In each case, the plasmonic response of a system to a specific internal or external stimulus represents the central design criterion. For colorimetry, the task of plasmonics is very direct, meaning that the plasmonic response of a material is evaluated directly. For this reason, the plasmonic material/substrate is often closely linked to the analytical question.
Building on this, SERS spectroscopy demonstrates the power of surface-enhanced analytics. Here, plasmonics serve to provide the enhancement as a means to an end. The central task is the detection of chemical information—often independent of the actual plasmonic material. In fact, the analysis is, in many cases, blind to the plasmonic material. This opens the door for optimizing the nanostructure for higher signal yields. In this overview, we have found various structural approaches to increase the sensitivity. The confined and localized enhancement in these structures gives access to unprecedented details about the chemistry of and at material interfaces and nanoparticle surfaces [131].
As a final thought, one needs to bear in mind that some questions persist regarding the enhancement mechanism in action. For multiparticle systems and complex nanostructures, the prediction of hot spot localization and intensity becomes increasingly challenging. Several examples have shown the surprising circumstance of highest SERS response at unexpected conditions. In retrospect, it is likely that a fair share of SERS studies in the literature might be affected by particle aggregation. For that reason, targeted investigations are necessary to explain such phenomena. Also, the accurate prediction of SERS activity is still challenging both on a single-particle level as well as in multiparticle assemblies. In view of these points, besides increasing the sensitivity, the sensing robustness of the system must be a central design criterion in the development.
C.K. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 799393 (NANOBIOME). Honest gratitude is addressed to Andreas Fery for his fruitful suggestions, his critical thinking, and his continued support.
The author declares no competing financial interest.
IntechOpen aims to ensure that original material is published while at the same time giving significant freedom to our Authors. To that end we maintain a flexible Copyright Policy guaranteeing that there is no transfer of copyright to the publisher and Authors retain exclusive copyright to their Work.
',metaTitle:"Publication Agreement - Chapters",metaDescription:"IN TECH aims to guarantee that original material is published while at the same time giving significant freedom to our authors. For that matter, we uphold a flexible copyright policy meaning that there is no transfer of copyright to the publisher and authors retain exclusive copyright to their work.\n\nWhen submitting a manuscript the Corresponding Author is required to accept the terms and conditions set forth in our Publication Agreement as follows:",metaKeywords:null,canonicalURL:"/page/publication-agreement-chapters",contentRaw:'[{"type":"htmlEditorComponent","content":"The Corresponding Author (acting on behalf of all Authors) and INTECHOPEN LIMITED, incorporated and registered in England and Wales with company number 11086078 and a registered office at 5 Princes Gate Court, London, United Kingdom, SW7 2QJ conclude the following Agreement regarding the publication of a Book Chapter:
\\n\\n1. DEFINITIONS
\\n\\nCorresponding Author: The Author of the Chapter who serves as a Signatory to this Agreement. The Corresponding Author acts on behalf of any other Co-Author.
\\n\\nCo-Author: All other Authors of the Chapter besides the Corresponding Author.
\\n\\nIntechOpen: IntechOpen Ltd., the Publisher of the Book.
\\n\\nBook: The publication as a collection of chapters compiled by IntechOpen including the Chapter. Chapter: The original literary work created by Corresponding Author and any Co-Author that is the subject of this Agreement.
\\n\\n2. CORRESPONDING AUTHOR'S GRANT OF RIGHTS
\\n\\n2.1 Subject to the following Article, the Corresponding Author grants and shall ensure that each Co-Author grants, to IntechOpen, during the full term of copyright and any extensions or renewals of that term the following:
\\n\\nThe aforementioned licenses shall survive the expiry or termination of this Agreement for any reason.
\\n\\n2.2 The Corresponding Author (on their own behalf and on behalf of any Co-Author) reserves the following rights to the Chapter but agrees not to exercise them in such a way as to adversely affect IntechOpen's ability to utilize the full benefit of this Publication Agreement: (i) reprographic rights worldwide, other than those which subsist in the typographical arrangement of the Chapter as published by IntechOpen; and (ii) public lending rights arising under the Public Lending Right Act 1979, as amended from time to time, and any similar rights arising in any part of the world.
\\n\\nThe Corresponding Author confirms that they (and any Co-Author) are and will remain a member of any applicable licensing and collecting society and any successor to that body responsible for administering royalties for the reprographic reproduction of copyright works.
\\n\\nSubject to the license granted above, copyright in the Chapter and all versions of it created during IntechOpen's editing process (including the published version) is retained by the Corresponding Author and any Co-Author.
\\n\\nSubject to the license granted above, the Corresponding Author and any Co-Author retains patent, trademark and other intellectual property rights to the Chapter.
\\n\\n2.3 All rights granted to IntechOpen in this Article are assignable, sublicensable or otherwise transferrable to third parties without the Corresponding Author's or any Co-Author’s specific approval.
\\n\\n2.4 The Corresponding Author (on their own behalf and on behalf of each Co-Author) will not assert any rights under the Copyright, Designs and Patents Act 1988 to object to derogatory treatment of the Chapter as a consequence of IntechOpen's changes to the Chapter arising from translation of it, corrections and edits for house style, removal of problematic material and other reasonable edits.
\\n\\n3. CORRESPONDING AUTHOR'S DUTIES
\\n\\n3.1 When distributing or re-publishing the Chapter, the Corresponding Author agrees to credit the Book in which the Chapter has been published as the source of first publication, as well as IntechOpen. The Corresponding Author warrants that each Co-Author will also credit the Book in which the Chapter has been published as the source of first publication, as well as IntechOpen, when they are distributing or re-publishing the Chapter.
\\n\\n3.2 When submitting the Chapter, the Corresponding Author agrees to:
\\n\\nThe Corresponding Author will be held responsible for the payment of the Open Access Publishing Fees.
\\n\\nAll payments shall be due 30 days from the date of the issued invoice. The Corresponding Author or the payer on the Corresponding Author's and Co-Authors' behalf will bear all banking and similar charges incurred.
\\n\\n3.3 The Corresponding Author shall obtain in writing all consents necessary for the reproduction of any material in which a third-party right exists, including quotations, photographs and illustrations, in all editions of the Chapter worldwide for the full term of the above licenses, and shall provide to IntechOpen upon request the original copies of such consents for inspection (at IntechOpen's option) or photocopies of such consents.
\\n\\nThe Corresponding Author shall obtain written informed consent for publication from people who might recognize themselves or be identified by others (e.g. from case reports or photographs).
\\n\\n3.4 The Corresponding Author and any Co-Author shall respect confidentiality rights during and after the termination of this Agreement. The information contained in all correspondence and documents as part of the publishing activity between IntechOpen and the Corresponding Author and any Co-Author are confidential and are intended only for the recipient. The contents may not be disclosed publicly and are not intended for unauthorized use or distribution. Any use, disclosure, copying, or distribution is prohibited and may be unlawful.
\\n\\n4. CORRESPONDING AUTHOR'S WARRANTY
\\n\\n4.1 The Corresponding Author represents and warrants that the Chapter does not and will not breach any applicable law or the rights of any third party and, specifically, that the Chapter contains no matter that is defamatory or that infringes any literary or proprietary rights, intellectual property rights, or any rights of privacy. The Corresponding Author warrants and represents that: (i) the Chapter is the original work of themselves and any Co-Author and is not copied wholly or substantially from any other work or material or any other source; (ii) the Chapter has not been formally published in any other peer-reviewed journal or in a book or edited collection, and is not under consideration for any such publication; (iii) they themselves and any Co-Author are qualifying persons under section 154 of the Copyright, Designs and Patents Act 1988; (iv) they themselves and any Co-Author have not assigned and will not during the term of this Publication Agreement purport to assign any of the rights granted to IntechOpen under this Publication Agreement; and (v) the rights granted by this Publication Agreement are free from any security interest, option, mortgage, charge or lien.
\\n\\nThe Corresponding Author also warrants and represents that: (i) they have the full power to enter into this Publication Agreement on their own behalf and on behalf of each Co-Author; and (ii) they have the necessary rights and/or title in and to the Chapter to grant IntechOpen, on behalf of themselves and any Co-Author, the rights and licenses expressed to be granted in this Publication Agreement. If the Chapter was prepared jointly by the Corresponding Author and any Co-Author, the Corresponding Author warrants and represents that: (i) each Co-Author agrees to the submission, license and publication of the Chapter on the terms of this Publication Agreement; and (ii) they have the authority to enter into this Publication Agreement on behalf of and bind each Co-Author. The Corresponding Author shall: (i) ensure each Co-Author complies with all relevant provisions of this Publication Agreement, including those relating to confidentiality, performance and standards, as if a party to this Publication Agreement; and (ii) remain primarily liable for all acts and/or omissions of each such Co-Author.
\\n\\nThe Corresponding Author agrees to indemnify and hold IntechOpen harmless against all liabilities, costs, expenses, damages and losses and all reasonable legal costs and expenses suffered or incurred by IntechOpen arising out of or in connection with any breach of the aforementioned representations and warranties. This indemnity shall not cover IntechOpen to the extent that a claim under it results from IntechOpen's negligence or willful misconduct.
\\n\\n4.2 Nothing in this Publication Agreement shall have the effect of excluding or limiting any liability for death or personal injury caused by negligence or any other liability that cannot be excluded or limited by applicable law.
\\n\\n5. TERMINATION
\\n\\n5.1 IntechOpen has a right to terminate this Publication Agreement for quality, program, technical or other reasons with immediate effect, including without limitation (i) if the Corresponding Author or any Co-Author commits a material breach of this Publication Agreement; (ii) if the Corresponding Author or any Co-Author (being an individual) is the subject of a bankruptcy petition, application or order; or (iii) if the Corresponding Author or any Co-Author (being a company) commences negotiations with all or any class of its creditors with a view to rescheduling any of its debts, or makes a proposal for or enters into any compromise or arrangement with any of its creditors.
\\n\\nIn case of termination, IntechOpen will notify the Corresponding Author, in writing, of the decision.
\\n\\n6. INTECHOPEN’S DUTIES AND RIGHTS
\\n\\n6.1 Unless prevented from doing so by events outside its reasonable control, IntechOpen, in its discretion, agrees to publish the Chapter attributing it to the Corresponding Author and any Co-Author.
\\n\\n6.2 IntechOpen has the right to use the Corresponding Author’s and any Co-Author’s names and likeness in connection with scientific dissemination, retrieval, archiving, web hosting and promotion and marketing of the Chapter and has the right to contact the Corresponding Author and any Co-Author until the Chapter is publicly available on any platform owned and/or operated by IntechOpen.
\\n\\n6.3 IntechOpen is granted the authority to enforce the rights from this Publication Agreement, on behalf of the Corresponding Author and any Co-Author, against third parties (for example in cases of plagiarism or copyright infringements). In respect of any such infringement or suspected infringement of the copyright in the Chapter, IntechOpen shall have absolute discretion in addressing any such infringement which is likely to affect IntechOpen's rights under this Publication Agreement, including issuing and conducting proceedings against the suspected infringer.
\\n\\n7. MISCELLANEOUS
\\n\\n7.1 Further Assurance: The Corresponding Author shall and will ensure that any relevant third party (including any Co-Author) shall, execute and deliver whatever further documents or deeds and perform such acts as IntechOpen reasonably requires from time to time for the purpose of giving IntechOpen the full benefit of the provisions of this Publication Agreement.
\\n\\n7.2 Third Party Rights: A person who is not a party to this Publication Agreement may not enforce any of its provisions under the Contracts (Rights of Third Parties) Act 1999.
\\n\\n7.3 Entire Agreement: This Publication Agreement constitutes the entire agreement between the parties in relation to its subject matter. It replaces and extinguishes all prior agreements, draft agreements, arrangements, collateral warranties, collateral contracts, statements, assurances, representations and undertakings of any nature made by or on behalf of the parties, whether oral or written, in relation to that subject matter. Each party acknowledges that in entering into this Publication Agreement it has not relied upon any oral or written statements, collateral or other warranties, assurances, representations or undertakings which were made by or on behalf of the other party in relation to the subject matter of this Publication Agreement at any time before its signature (together "Pre-Contractual Statements"), other than those which are set out in this Publication Agreement. Each party hereby waives all rights and remedies which might otherwise be available to it in relation to such Pre-Contractual Statements. Nothing in this clause shall exclude or restrict the liability of either party arising out of its pre-contract fraudulent misrepresentation or fraudulent concealment.
\\n\\n7.4 Waiver: No failure or delay by a party to exercise any right or remedy provided under this Publication Agreement or by law shall constitute a waiver of that or any other right or remedy, nor shall it preclude or restrict the further exercise of that or any other right or remedy. No single or partial exercise of such right or remedy shall preclude or restrict the further exercise of that or any other right or remedy.
\\n\\n7.5 Variation: No variation of this Publication Agreement shall be effective unless it is in writing and signed by the parties (or their duly authorized representatives).
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\\n\\nAny modification to or deletion of a provision or part-provision under this clause shall not affect the validity and enforceability of the rest of this Publication Agreement.
\\n\\n7.7 No partnership: Nothing in this Publication Agreement is intended to, or shall be deemed to, establish or create any partnership or joint venture or the relationship of principal and agent or employer and employee between IntechOpen and the Corresponding Author or any Co-Author, nor authorize any party to make or enter into any commitments for or on behalf of any other party.
\\n\\n7.8 Governing law: This Publication Agreement and any dispute or claim (including non-contractual disputes or claims) arising out of or in connection with it or its subject matter or formation shall be governed by and construed in accordance with the law of England and Wales. The parties submit to the exclusive jurisdiction of the English courts to settle any dispute or claim arising out of or in connection with this Publication Agreement (including any non-contractual disputes or claims).
\\n\\nLast updated: 2020-11-27
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The Corresponding Author (acting on behalf of all Authors) and INTECHOPEN LIMITED, incorporated and registered in England and Wales with company number 11086078 and a registered office at 5 Princes Gate Court, London, United Kingdom, SW7 2QJ conclude the following Agreement regarding the publication of a Book Chapter:
\n\n1. DEFINITIONS
\n\nCorresponding Author: The Author of the Chapter who serves as a Signatory to this Agreement. The Corresponding Author acts on behalf of any other Co-Author.
\n\nCo-Author: All other Authors of the Chapter besides the Corresponding Author.
\n\nIntechOpen: IntechOpen Ltd., the Publisher of the Book.
\n\nBook: The publication as a collection of chapters compiled by IntechOpen including the Chapter. Chapter: The original literary work created by Corresponding Author and any Co-Author that is the subject of this Agreement.
\n\n2. CORRESPONDING AUTHOR'S GRANT OF RIGHTS
\n\n2.1 Subject to the following Article, the Corresponding Author grants and shall ensure that each Co-Author grants, to IntechOpen, during the full term of copyright and any extensions or renewals of that term the following:
\n\nThe aforementioned licenses shall survive the expiry or termination of this Agreement for any reason.
\n\n2.2 The Corresponding Author (on their own behalf and on behalf of any Co-Author) reserves the following rights to the Chapter but agrees not to exercise them in such a way as to adversely affect IntechOpen's ability to utilize the full benefit of this Publication Agreement: (i) reprographic rights worldwide, other than those which subsist in the typographical arrangement of the Chapter as published by IntechOpen; and (ii) public lending rights arising under the Public Lending Right Act 1979, as amended from time to time, and any similar rights arising in any part of the world.
\n\nThe Corresponding Author confirms that they (and any Co-Author) are and will remain a member of any applicable licensing and collecting society and any successor to that body responsible for administering royalties for the reprographic reproduction of copyright works.
\n\nSubject to the license granted above, copyright in the Chapter and all versions of it created during IntechOpen's editing process (including the published version) is retained by the Corresponding Author and any Co-Author.
\n\nSubject to the license granted above, the Corresponding Author and any Co-Author retains patent, trademark and other intellectual property rights to the Chapter.
\n\n2.3 All rights granted to IntechOpen in this Article are assignable, sublicensable or otherwise transferrable to third parties without the Corresponding Author's or any Co-Author’s specific approval.
\n\n2.4 The Corresponding Author (on their own behalf and on behalf of each Co-Author) will not assert any rights under the Copyright, Designs and Patents Act 1988 to object to derogatory treatment of the Chapter as a consequence of IntechOpen's changes to the Chapter arising from translation of it, corrections and edits for house style, removal of problematic material and other reasonable edits.
\n\n3. CORRESPONDING AUTHOR'S DUTIES
\n\n3.1 When distributing or re-publishing the Chapter, the Corresponding Author agrees to credit the Book in which the Chapter has been published as the source of first publication, as well as IntechOpen. The Corresponding Author warrants that each Co-Author will also credit the Book in which the Chapter has been published as the source of first publication, as well as IntechOpen, when they are distributing or re-publishing the Chapter.
\n\n3.2 When submitting the Chapter, the Corresponding Author agrees to:
\n\nThe Corresponding Author will be held responsible for the payment of the Open Access Publishing Fees.
\n\nAll payments shall be due 30 days from the date of the issued invoice. The Corresponding Author or the payer on the Corresponding Author's and Co-Authors' behalf will bear all banking and similar charges incurred.
\n\n3.3 The Corresponding Author shall obtain in writing all consents necessary for the reproduction of any material in which a third-party right exists, including quotations, photographs and illustrations, in all editions of the Chapter worldwide for the full term of the above licenses, and shall provide to IntechOpen upon request the original copies of such consents for inspection (at IntechOpen's option) or photocopies of such consents.
\n\nThe Corresponding Author shall obtain written informed consent for publication from people who might recognize themselves or be identified by others (e.g. from case reports or photographs).
\n\n3.4 The Corresponding Author and any Co-Author shall respect confidentiality rights during and after the termination of this Agreement. The information contained in all correspondence and documents as part of the publishing activity between IntechOpen and the Corresponding Author and any Co-Author are confidential and are intended only for the recipient. The contents may not be disclosed publicly and are not intended for unauthorized use or distribution. Any use, disclosure, copying, or distribution is prohibited and may be unlawful.
\n\n4. CORRESPONDING AUTHOR'S WARRANTY
\n\n4.1 The Corresponding Author represents and warrants that the Chapter does not and will not breach any applicable law or the rights of any third party and, specifically, that the Chapter contains no matter that is defamatory or that infringes any literary or proprietary rights, intellectual property rights, or any rights of privacy. The Corresponding Author warrants and represents that: (i) the Chapter is the original work of themselves and any Co-Author and is not copied wholly or substantially from any other work or material or any other source; (ii) the Chapter has not been formally published in any other peer-reviewed journal or in a book or edited collection, and is not under consideration for any such publication; (iii) they themselves and any Co-Author are qualifying persons under section 154 of the Copyright, Designs and Patents Act 1988; (iv) they themselves and any Co-Author have not assigned and will not during the term of this Publication Agreement purport to assign any of the rights granted to IntechOpen under this Publication Agreement; and (v) the rights granted by this Publication Agreement are free from any security interest, option, mortgage, charge or lien.
\n\nThe Corresponding Author also warrants and represents that: (i) they have the full power to enter into this Publication Agreement on their own behalf and on behalf of each Co-Author; and (ii) they have the necessary rights and/or title in and to the Chapter to grant IntechOpen, on behalf of themselves and any Co-Author, the rights and licenses expressed to be granted in this Publication Agreement. If the Chapter was prepared jointly by the Corresponding Author and any Co-Author, the Corresponding Author warrants and represents that: (i) each Co-Author agrees to the submission, license and publication of the Chapter on the terms of this Publication Agreement; and (ii) they have the authority to enter into this Publication Agreement on behalf of and bind each Co-Author. The Corresponding Author shall: (i) ensure each Co-Author complies with all relevant provisions of this Publication Agreement, including those relating to confidentiality, performance and standards, as if a party to this Publication Agreement; and (ii) remain primarily liable for all acts and/or omissions of each such Co-Author.
\n\nThe Corresponding Author agrees to indemnify and hold IntechOpen harmless against all liabilities, costs, expenses, damages and losses and all reasonable legal costs and expenses suffered or incurred by IntechOpen arising out of or in connection with any breach of the aforementioned representations and warranties. This indemnity shall not cover IntechOpen to the extent that a claim under it results from IntechOpen's negligence or willful misconduct.
\n\n4.2 Nothing in this Publication Agreement shall have the effect of excluding or limiting any liability for death or personal injury caused by negligence or any other liability that cannot be excluded or limited by applicable law.
\n\n5. TERMINATION
\n\n5.1 IntechOpen has a right to terminate this Publication Agreement for quality, program, technical or other reasons with immediate effect, including without limitation (i) if the Corresponding Author or any Co-Author commits a material breach of this Publication Agreement; (ii) if the Corresponding Author or any Co-Author (being an individual) is the subject of a bankruptcy petition, application or order; or (iii) if the Corresponding Author or any Co-Author (being a company) commences negotiations with all or any class of its creditors with a view to rescheduling any of its debts, or makes a proposal for or enters into any compromise or arrangement with any of its creditors.
\n\nIn case of termination, IntechOpen will notify the Corresponding Author, in writing, of the decision.
\n\n6. INTECHOPEN’S DUTIES AND RIGHTS
\n\n6.1 Unless prevented from doing so by events outside its reasonable control, IntechOpen, in its discretion, agrees to publish the Chapter attributing it to the Corresponding Author and any Co-Author.
\n\n6.2 IntechOpen has the right to use the Corresponding Author’s and any Co-Author’s names and likeness in connection with scientific dissemination, retrieval, archiving, web hosting and promotion and marketing of the Chapter and has the right to contact the Corresponding Author and any Co-Author until the Chapter is publicly available on any platform owned and/or operated by IntechOpen.
\n\n6.3 IntechOpen is granted the authority to enforce the rights from this Publication Agreement, on behalf of the Corresponding Author and any Co-Author, against third parties (for example in cases of plagiarism or copyright infringements). In respect of any such infringement or suspected infringement of the copyright in the Chapter, IntechOpen shall have absolute discretion in addressing any such infringement which is likely to affect IntechOpen's rights under this Publication Agreement, including issuing and conducting proceedings against the suspected infringer.
\n\n7. MISCELLANEOUS
\n\n7.1 Further Assurance: The Corresponding Author shall and will ensure that any relevant third party (including any Co-Author) shall, execute and deliver whatever further documents or deeds and perform such acts as IntechOpen reasonably requires from time to time for the purpose of giving IntechOpen the full benefit of the provisions of this Publication Agreement.
\n\n7.2 Third Party Rights: A person who is not a party to this Publication Agreement may not enforce any of its provisions under the Contracts (Rights of Third Parties) Act 1999.
\n\n7.3 Entire Agreement: This Publication Agreement constitutes the entire agreement between the parties in relation to its subject matter. It replaces and extinguishes all prior agreements, draft agreements, arrangements, collateral warranties, collateral contracts, statements, assurances, representations and undertakings of any nature made by or on behalf of the parties, whether oral or written, in relation to that subject matter. Each party acknowledges that in entering into this Publication Agreement it has not relied upon any oral or written statements, collateral or other warranties, assurances, representations or undertakings which were made by or on behalf of the other party in relation to the subject matter of this Publication Agreement at any time before its signature (together "Pre-Contractual Statements"), other than those which are set out in this Publication Agreement. Each party hereby waives all rights and remedies which might otherwise be available to it in relation to such Pre-Contractual Statements. Nothing in this clause shall exclude or restrict the liability of either party arising out of its pre-contract fraudulent misrepresentation or fraudulent concealment.
\n\n7.4 Waiver: No failure or delay by a party to exercise any right or remedy provided under this Publication Agreement or by law shall constitute a waiver of that or any other right or remedy, nor shall it preclude or restrict the further exercise of that or any other right or remedy. No single or partial exercise of such right or remedy shall preclude or restrict the further exercise of that or any other right or remedy.
\n\n7.5 Variation: No variation of this Publication Agreement shall be effective unless it is in writing and signed by the parties (or their duly authorized representatives).
\n\n7.6 Severance: If any provision or part-provision of this Publication Agreement is or becomes invalid, illegal or unenforceable, it shall be deemed modified to the minimum extent necessary to make it valid, legal and enforceable. If such modification is not possible, the relevant provision or part-provision shall be deemed deleted.
\n\nAny modification to or deletion of a provision or part-provision under this clause shall not affect the validity and enforceability of the rest of this Publication Agreement.
\n\n7.7 No partnership: Nothing in this Publication Agreement is intended to, or shall be deemed to, establish or create any partnership or joint venture or the relationship of principal and agent or employer and employee between IntechOpen and the Corresponding Author or any Co-Author, nor authorize any party to make or enter into any commitments for or on behalf of any other party.
\n\n7.8 Governing law: This Publication Agreement and any dispute or claim (including non-contractual disputes or claims) arising out of or in connection with it or its subject matter or formation shall be governed by and construed in accordance with the law of England and Wales. The parties submit to the exclusive jurisdiction of the English courts to settle any dispute or claim arising out of or in connection with this Publication Agreement (including any non-contractual disputes or claims).
\n\nLast updated: 2020-11-27
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