This book describes a comprehensive overview of electro-chemical sensors and biosensors for the analyses, investigation, and monitoring of the most significant unsafe analytes in the ecological as well as environmental field in industry, in treatment plants, and in environmental research. The contributed chapters stretch the reader a comprehensive study, state-of-the-art picture of the field of electro-chemical sensors or biosensors appropriate to environmental analytes, from the theoretical principles of their design to their implementation, realization, and potential application. It covers the most recent techniques and nanocomposites/nanomaterials for the preparation, construction, validation, analyses, and design of electro-chemical sensors/biosensors for bio-analytical, clinical, and environmental applications—emphasizing the latest classes of selective, sensitive, robust, fast response, stable, electro-chemical sensors as well as electrochemical biosensors for in vivo/vitro diagnosis.
Development in advanced nanotechnology and the conservatory of innovative chemical sensors, biosensors, ionic sensors with various composites/materials and nanodevices has been a regulating key task in the fabrication and improvement of very precise, perceptive, accurate, sophisticated, sensitive, and consistent efficient chemical sensors [1–3]. The exploration for even tiny electrodes accomplished in nano-level imaging and controlling of doped nanomaterials, doping agents (host-guest), biological, chemical, pathological samples, and chemical sensors has recently extended the attention of awareness of the scientist, mainly for control monitoring, owing to the amplifying essential for environmental safety and health monitoring [4–6]. Recently, great attention is provided for the detection of various unsafe, carcinogenic, toxic, hazardous chemicals, or biomolecules to live safely and as well as to prevent the ecological system from harmful effects of toxins [7–9].
Ronkainen et al. describe the enzyme-based electrochemical glutamate biosensor development, which has been proposed to play a significant role in various neurological and psychiatric disorders. In this contribution, the design, construction, and optimization of enzyme-based electrochemical biosensors for in vivo and in vitro detection of glutamate were discussed in this contribution [10–17]. Various glutamate biosensors have been discussed, including the developed glutamate monitoring dynamic levels of extracellular glutamate in the living brain tissue adding to the current medical knowledge of these complex neurotransmitter systems and ultimately impacting treatment plans [18–21]. More significantly, glutamate biosensors have been used in environmental monitoring, in the fermentation industry, and in the food industry for determination of Monosodium glutamate (MSG), a common flavor-enhancing food additive. With continuous developments in molecular biology, nanofabrication methods, immobilization methods of biomolecules and multiplexing capabilities, the production of sensitive, selective, fast, and easy-to-use biosensors for quantification of glutamate, and other neurotransmitters will be feasible in the not too distant future.
Qijin et al. approached some graphene paper-based electro-chemical sensors to illustrate recent advances in the research and development of 2D graphene papers as new and noble materials for electro-chemical sensors. It covers the design, fabrication, functionalization, and application evaluation of graphene papers. Precise monitoring of chemical or biological processes is of extreme importance for medical and biological applications. Electro-chemical sensors can ideally fulfill that goal by converting a chemical or biological response into a processable and quantifiable signal. In the past two decades, intensive research and development of electro-chemical sensors have enabled to fabricate different types of devices [22–31]. After the development of many successful commercial electro-chemical sensors in the classic configurations, currently, there is a notable transition and increasing demands for the development of flexible and wearable sensors. The development of flexible electro-chemical sensors depends crucially on the discovery and preparation of freestanding and flexible new materials. They first summarized the mainstream methods for fabrication of graphene papers/membranes with the focus on chemical vapor deposition techniques and solution-processing assembly. A large portion of this work is devoted to the highlights of specific functionalization of graphene papers with polymer and nanoscale functional building blocks for electrochemical sensing purposes. In terms of electrochemical sensing applications, the emphasis is on enzyme-graphene and nanoparticle-graphene paper-based systems for detection of glucose. We conclude this chapter with brief remarks and an outlook. In short, worldwide researchers have explored graphene paper–based sensors by exploiting their unique advantages including high sensitivity, conductivity, and in-situ sensing. The recent research advances suggest that graphene paper-based materials could play a significant role in developing flexible sensors and electronic devices due to their intriguing structural and functional features.
Murray et al. focused on managing H2O cross-sensitivity using composite electrolyte “NOx sensors”. They approached NOx sensors composed of PSZ, FSZ, and PSZ–FSZ composite electrolytes which were investigated using impedance spectroscopy under dry and humidified gas conditions. The microstructural properties, NOx sensitivity, oxygen partial pressure and temperature dependence, as well as the response time of the sensors composed of the various electrolytes were characterized in order to interpret the electrochemical response with respect to water cross-sensitivity. In this approach, impedance spectroscopy was used to interpret the electrochemical response of NOx sensors composed of PSZ, FSZ, and PSZ–FSZ composite electrolytes during operation under dry and humidified gas conditions. Analysis of the electrochemical responses of the 50PSZ–50FSZ-based sensors indicated PSZ contributed to lower water cross-sensitivity, while FSZ promoted NOx sensitivity. Finally, sensors composed of the 50PSZ–50FSZ composite electrolyte demonstrated significant sensitivity to NO and low cross-sensitivity to water with negligible temperature dependence [32–35].
Lutic et al. describe electro-chemical sensors for monitoring indoor and outdoor air pollution. They approached a comprehensive presentation of the most common electro-chemical sensors used in real monitoring applications of air purity testing. The air quality monitoring stations based on electro-chemical sensors are nowadays used to determine the global pollution index of the atmospheric air, in order to prevent the risks toward human health and damage of environment, especially in the highly populated and industrialized urban areas. The electro-chemical gas sensors are nowadays indispensable in the monitoring of the atmosphere quality, especially due to pollutants associated with human activities. Carbon monoxide, sulfur oxides, hydrogen sulfide, and nitrogen oxides are only a few of species which can seriously damage the environment equilibrium by smog formation, acid rain, soil deterioration, water contamination as well as some direct damages on the human health [36–38]. The electrochemical gas sensing is based on gas oxidation or reducing reactions on sensing surfaces with catalytic potential, surfaces which suffer noticeable charge changes, that can be amplified and processed in order to generate a signal. The electro-chemical sensors are fast, reliable, small and cheap; therefore, their use covers nowadays the exhaust systems from automotives, domestic/residential gas detection, and leak checkers. Respecting the rated voltage as said by the manufacturer, using the sensor in the right temperature range, avoiding the deterioration due to exposure to humidity, avoiding contamination with various chemicals, lack of sudden exposure to extreme temperatures, and avoiding the mechanical shocks are basic conditions to preserve their work function and accuracy.
Lee et al. have focused on fabrication and characteristics of metal-loaded mixed metal oxides gas sensors for the detection of toxic gases for environmental purposes. They approached developing gas sensors which permit individuals to circumvent poisonous gases that may be produced in spaces with residues of inorganic/organic waste with certain temperature at 50°C or above. The response, sensitivity, and selectivity of these gas sensors to types of carcinogenic gases such as H2S, toluene, and aldehyde were examined. The thick-film semiconductor sensors that detect some toxic gases were fabricated using nano-sized sensing materials powder (SnO2, WO3, and ZnO), and these were prepared via sol-gel and precipitation methods. Response to various lethal gases was measured and is defined as the ratio (Ra/Rg) of the resistance of the sensor film in air to the resistance of the film in toxic gas. Generally, semiconductor metal-oxide gas sensors can be used for diverse applications, ranging from equipment to monitor environmental and occupational safety to facilitating quality assurance through novel measurement. The nature of the gas-sensitive material and the concentration of the target gas (usually a few ppb~ppm) determine the measuring range and limitations of the device [39–41].
Zhang describes the potential application of nanosensors in dissolved gases for the detection in oil-insulated transformers in this contribution. Here, it is approached on the adsorption processes between modified CNTs (CNTs-OH, Ni-CNTs) and dissolved gases in transformers oil including C2H2, C2H4, C2H6, CH4, CO, and H2 which have been simulated based on the first principle theory. Additionally, the density of states, adsorption energy, charge transfer amount, and adsorption distance of adsorption process between CNTs and dissolved gas were also calculated in his chapter. Two kinds of sensors, mixed acid-modified CNTs and NiCl2-modified CNTs, were prepared to conduct the dissolved gases response experiment. Afterward, the gas response mechanisms were investigated. Finally, the results between response experiment and theoretical calculation were compared, reflecting a good coherence with each other. The carbon nanotube (CNT) based gas sensors possess a relatively high sensitivity and fine linearity and could be employed in dissolved gas analysis equipment in the transformer [42–47].
Finally, this book generally reviews the recent and advanced methods and substantial applications of biosensors, gas sensor and chemical sensors. Contributed chapters are scratched by expert scientists and professors in the electrochemical sensor field. This book aims to make a connection between undergraduates, post-graduates, graduates, and scientists on their researches in sensor development based on enzyme-based sensors, graphene-based sensors, NOx sensors, gas sensors, hazardous and toxic gas sensors, and nano-sensors in environmental and biomedical sciences in order to initiate researchers into various sensors study in as straightforward a way as possible and as well as present the scientist the opportunities offered by the health care science and ecological fields. However, each chapter delivers methodological details beyond the level originally in representative journal articles and explores the potential applications of biological and chemical sensors to a substantial level in health care, real clinical, food, industrial, cancer diagnostics, biomedical, environmental science and detection of infectious organisms, also providing a brochure for the future as well as in the safety and security arena. The primary target audience for this book “Electrochemical Sensors Technology” includes students, researchers, technologists, physicists, chemists, biologists, engineers, and professionals who are interested in bio, chemi, and gas sensors and associated topics.