Biomedical Applications of Superparamagnetic Iron Oxide Nanoparticles (SPIONS) as a Theranostic Agent

Abstract

Nowadays, nanoparticles are used in a variety of biological applications where they enhance treatments and laboratory tests. Due to their distinctive properties and minor adverse effects, nanoparticles are being used more specifically for medication delivery, not only in the treatment of cancer but also for other diseases. Magnetic nanoparticles like SPION (superparamagnetic Iron Oxide nanoparticles) are regarded to be the most viable in the midst of these materials. SPION are frequently used in biomedical applications due to their low cost and lack of toxicity. Within the developing field of nanomedicine, superparamagnetic iron oxide nanoparticles (SPION) are basic technological classes that have been widely studied for cancer imaging and treatment. Additionally, SPION employ super paramagnets, which seem to be beneficial for focusing on particular tumor areas within a body. For instance, the superparamagnetic abilities of magnetite (Fe₃O₄), which are frequently utilized in delivery of drug, diagnosis and therapy. SPION was envisioned as a tool for the “golden therapeutic era” since it minimized cellular absorption by macrophages, targeted cancer cells preferentially while sparing healthy cells, monitored cancer cells before and after therapy, and controlled drug release. In order to give a concise overview of SPION, there will be focus on their biomedical applications includes hyperthermia (HT), magnetic resonance imaging (MRI), magnetic drug targeting (MDT), gene delivery as well as nanomedicine.

1. Introduction

SPION (Super magnetic iron oxide nanoparticles) are the nanoparticles with a functionalized shell surrounding an iron oxide core. These are iron oxide crystals {magnetite (Fe₃O₄) or maghemite (γ-Fe₂O₃)} with a shell that can be altered to improve stability in aqueous conditions and to alter the biochemical properties for a wide range of applications in biomedical sectors [1, 2]. The scientific community has recently become very interested in SPION due to their intriguing potential diagnostic and therapeutic applications. They have wide range of biomedical applications such as MRI, dual modality MRI/computed tomography (CT), magnetic fluid hyperthermia (MFH), biosensors, drug delivery as well as bio- separation [3]. SPION are a unique contrast agent for magnetic resonance imaging and a fascinating family of tracers for nuclear medicine due to their modifiable surface and core properties. A contrast agent can accelerate the relaxation rate of water, which is known as relaxation rates, since MRI evaluates the change in magnetic moment of water protons after applying radiofrequency (RF) pulses. In essence, after being excited by RF pulses, protons return to their equilibrium state, which is longitudinal T₁ relaxation. Transfer (T₂) relaxation is the exchange of the spin angular momentum between the protons (Figure 1).

Figure 1.

Showing physiochemical properties of SPIONs [4].

SPION exhibit contrast enhancing behavior, engage with nearby water molecules and speed up the rate at which water protons relax. The T₁ relaxation times are sped up by the contrast agents. The regions where SPION are taken up typically have a lower MR a signal intensity, which causes those regions to appear darker in MRI. Transfer (T₂) relaxation is the exchange of protons’ spin angular momentum. SPION act as a contrast agent, interact with nearby water molecules, and speed up the rate at which water protons relax. The T₁ relaxation and/or T₂ relaxation times are sped up by the contrast agents. The areas where SPION are taken up typically have a lower MR signal intensity, which causes those areas to appear darker in MRI [5, 6, 7, 8]. The current chapter comprehensively reviews the biomedical applications of SPION in theranostic area (Figure 2).

Figure 2.

Showing biomedical applications of SPIONs [9].

2. Synthesis and biomedical applications of SPIONS

2.1 Synthesis methods

The morphology as well as composition both affects the magnetic properties of the Iron oxide nanoparticles. In order to ensure control over the particle’s size, shape, size distribution as well as crystallinity, the method of synthesis must be carefully chosen. SPION can be created by using as variety of techniques, including chemical, physical and biosynthetic ones [10, 11, 12, 13].

2.1.1 Co-precipitation

The co-precipitation technique, one of the most straightforward and effective synthesis methods, relies on the addition of a weak or strong base to precipitate Fe²⁺ and Fe³⁺ aqueous salt solutions simultaneously. This process is primarily used to synthesize SPION commercially. Several artificial parameters affect the size, shape and the composition of iron oxide nanoparticles, such as Fe²⁺/Fe³⁺ ratio, temperature, pH, and salt type (chloride, nitrate, sulphate, perchlorate), as well as the kind of base employed (NaOH, NH₄OH, Na₂CO₃). This technique is one of the most economical ways to make SPION with the right magnetic properties in high degree of polydispersity and little crystallinity. A number of modified versions of this technique have been developed to address these drawbacks [14, 15, 16]. These for example, include in vivo co-precipitation in a carboxyl-functionalized polymer matrix, assistance from ultrasound, the use of alkanolamines as base, the preparation of Fe₃O₄ nanoparticles under a static magnetic field and at the end co-precipitation of FeCl₃.6H₂O, FeSO₄.7H₂O, and Gd(NO₃)₃ aqueous solutions is done by addition of NaOH [17, 18, 19, 20].

2.1.2 Microemulsion

Microemulsion systems are the isotropic dispersion of two immiscible liquids that are thermodynamically stable. Essentially, there are two types of microemulsions: oil-in-water (o/w; normal micelles) and water-in-oil (w/o; reversed micelles). Usually, the dispersed phase acts as a nano/micro-reactor, offering a constrained setting for the initiation and controlled development of nano- and microparticles. Micellar microemulsion systems are created using a variety of amphiphilic surfactants, such as dioctyl sodium dodecyl sulphate (DSS), cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS), and polyethoxylates (such as Tween-20 and -80) [14]. The main benefit of using microemulsion methodology to prepare SPION is the ability to control the nanoparticle size by varying the size of the micelles. Furthermore, a rise in the particle’s polydispersity is seen, which is likely caused by the relatively homogenous size of micelles. The typical low and constrained reaction temperature, which leads to SPION with poor crystallinity and low yields, is a drawback of microemulsion synthesis. The crystallinity of the particles produced by this method can be increased by thermal annealing the synthesized iron oxide or maintaining the micelle structure at high reaction temperatures [12, 21, 22].

2.1.3 Thermal decomposition

By thermally decomposing organoiron precursors in high-boiling-point organic solvents with stabilizing surfactants, SPION with excellent size and shape control, narrow size distribution, and good crystallinity can be produced [23, 24]. Oleic acid, oleylamine, fatty acids, and hexadecylamine are examples of amphiphilic surfactants that enable fine-tuning of the nucleation and growth kinetics of the nanoparticles. The presence of the surfactant in the reaction mixture and the high reaction temperatures produce samples with excellent size dispersion and crystallinity. However, because this method involves the synthesis of toxic chemicals like iron pentacarbonyl, chloroform, and hexane, it is not particularly eco-friendly. Furthermore, a further surface modification step is required to produce water-dispersible and biocompatible nanoparticles that are helpful for biomedical applications because the surface of the magnetic nanoparticles has a hydrophobic coating. Control over morphology and nanoparticle size when using the thermal decomposition method to create SPION is highly dependent on reaction time, reaction temperature, and the ratio of precursor to surfactant [25].

2.1.4 Sol: gel

The sol-gel method, which is frequently used for the production of silica-coated SPION, is based on the condensation and hydrolysis of tetraethyl orthosilicate (TEOS) in ethanol and 30% aqueous H₂O₂ with Fe³⁺ solutions to create colloidal sols. A 3D iron oxide network is then created by gelling the sol through a chemical reaction or solvent removal. After drying and solvent removal, the formed gel needs to be crushed in order to obtain iron oxide nanoparticles. When surfactant is added before gelation, the system’s free energy is reduced, which causes the formation of nanoscale iron oxides without the development of a 3D network. A simple method for producing high yields of relatively large and monodisperse nanoparticles in ambient conditions is the sol-gel synthesis technique. But because the sol-gel method is used at room temperature, additional heating is required to produce the desired crystalline structures. The technique also produces contaminated by-products, necessitating post-treatment purification. The parameters that affect the SPION gel’s structure and properties are temperature, pH, the solvent being used, and the concentration of salt precursors. TEOS and ammonia concentrations are typically used to adjust the silica shell’s thickness (Table 1) [26, 27, 43].

Methods of synthesis	Reactants used	Temperature during reaction (°C)	Pressure during reaction(psi)	Time taken during synthesis (hrs.)	Size distribution (nm)	Saturated magnetization at room temp(emu/g)	References
Thermal decomposition (liquid phase)	Organometallic compound (Fe(acac)3/Fe (CO)5)	100–400	14.7	20–24	4–20	20–85	[26, 27, 28, 29, 30]
Thermal decomposition (gas phase)	Fe(CO)5, Fe(C2H5)2 (Ferrocene)	125–1000	5.8–14.7	0.0041–0.16	6–100	20–45	[30, 31, 32]
Co-precipitation	FeCl3, FeCl2/FeSO4, NaOH/NH4OH	25–70	14.7	0.5–1	3–15	65–85	[30, 33]
Reduced co-precipitation	FeCl3, Na2SO3, NaOH/NH4OH	25–70	14.7	0.5–1	3–15	65–85	[30, 34]
Hydrothermal	Variable	80–160	Up to 2000	0.5–48	3–15	5–75	[30, 35]
Microemulsion	FeCl3, FeCl2/FeSO4, NaOH/NH4OH	4–90	14.7	3–20	3–12	30–60	[30, 36]
Mechanical	Fe (powder), FeCl2, FeCL3	Room Temperature	Ambient	1–48	20–100	60–146	[37, 38, 39]
Sonochemical decomposition	Fe (CO)5, Fe(acac)3, FeCl2, FeCl3	0–50	Ambient	0.5–8	5–30	30–80	[30, 40, 41, 42]

Table 1.

Iron oxide nanoparticle: Synthesis methods and reaction parameters of SPION.

3. Biomedical applications of SPION

As SPION are mainly used due to their main features such as their size, surface charge, shape, surface stability and biocompatibility. There are many uses of SPION in biomedicine, which are listed below: MRI, drug delivery, hyperthermia, cell labeling and separation, aptamers, biosensors etc. (Figure 3) [30].

Figure 3.

Showing SPIONs application in biomedicine [30].

3.1 Drug delivery

The Transmission of a remedial agent to a recommended site in the body is known as drug delivery. Drug delivery to directed disease is a critical step in the treatment of a variety of conditions, including cardiac disease, microbial attack and cancer. For targeted drug delivery of many diseases different kinds of magnetic nanoparticles are used. For example, in detection lesions in the liver tumor at a 23 mm level. SPION have been used by clinical imaging. For the treatment of MCF-5 breast cancer, drug administration and MRI monitoring have also been studied [39, 44, 45]. In the whole body, chemotherapy causes serious damage, so it is important to focus selectively on cancer cells to create targeted therapies. For higher doses of drugs, the targeting strategy should also increase the effectiveness of drugs without being limited by the harm to healthy tissue. For the SPION-based drug delivery system to be effective, many important criteria must be considered.in order to link targeting units, the carrier should provide a functional group and also provide the delivery system with suitable hydrophily, so that it can easily disperse into aqueous environment (Table 2) [8].

Functional molecules	Structure of DDS	Application	Results	References
Methotrexate	via a self-assembled monolayer PEG it immobilized on the surface of the iron oxide nanoparticles	Through MRI follow-up drug administration to brain tumors	High absorption of targeted nanoparticles, non-toxic methotrexate in vitro, significantly improved contrast	[46]
Methotrexate targeting folate receptor	Iron oxide NPs converted with APTES and linked by covalence with Methotrexate	For therapeutic treatment and imaging of cervical tumors and breast	In cells there is greater absorption of nanoparticles targeted with the folate receptor	[47]
Folate	Nuclei of SPIONs covered with a mixture of the triblock copolymer methoxy PEG-b-poly (methacrylic acid -co-n-butyl methacrylate)-b-poly (glycerol monomethacrylate) and the folate-conjugated block copolymer folate-PEG-b-poly (glycerol monomethacrylate) loaded with doxorubicin	For the treatment of cancer of cervix	The Targeting strategy improved absorption of nanoparticles and cytotoxicity	[48]
Folate	Incorporated inside Pluronic F127 micelles is folate iron oxide	Magnetic resonance imaging and medication administration	Absorption in the KB unit	[49]
Murine melanoma antigens, hgp10025–33	Murine melanoma antigens is brought by SPIONS,hgp10025–33	Administration of a murine melanoma antigens	Effective adoption of nanoparticles by engineers	[50]
Anti-Prostate-specific membrane antigen	A nanocomposite with quantum dots conjugated to the surface and an internally embedded PS matrix that is spherical, high fraction of SPIONs+PLGA+paclitaxel load	Prostate cancer imaging and targeting, medicine storage	Considerable targeting	[51]
LHRH (Luteinizing hormone releasing hormone)	PEG and LHRG-coated SPIONs poly(propyleneimine) generation 5 dendrimer siRNA complex	Drug delivery	Improve the internalization of cancer cells and increase the effectiveness of in vitro genetic suppression	[52]
LHRH	Conjugated SPIONs with LHRH	Treatment for human breast cancer tumors and metastases	The targeted nanoparticles had an accumulation a 12-multiplied by the accumulation of breast and lung metastases in vivo	[53]

Table 2.

Showing use of SPION in drug carrier and preclinical studies.

3.2 Bioimaging

In bioimaging and clinical purpose magnetic nanoparticles show great scientific interest because of their unique properties. At molecular and cellular level magnetic resonance imaging (MRI) is one of the strongest techniques used in biomedical imaging. In magnetic resonance imaging (MRI), many magnetic nanoparticles are used as a contrast medium, such as SPION, the core, magnetic gel nanoparticles and iron oxide. In these SPION demonstrate an important role in differentiating pathogenic and healthy cells. Because of the high resolution and capability of 3D imaging MRI provides information about soft tissue as well as for the detection of intra-tumor cancerous tissue. SPION and magnetic nanoparticles of iron oxide have aroused major interest in the administration of cancer drugs over the last decades [39].

3.3 Cell labeling and separation

There is numerous SPION cell labelling techniques that can be applied, each with a different goal in mind. There are three main categories that they fall under:

1. In-vitro methods (such as endocytosis, transfection agents, magnetofection, and electroporation);

2. In-vivo cell labelling by reticuloendothelial system (RES) through systemic application; and

3. receptor-mediated binding and internalization of SPION by targeted cells (e.g., targeted labelling and imaging). Stem cell tracking and monitoring for cell transplantation therapy reasons is one of the uses for cell labelling [52]. Living organisms, such as peptides, proteins, large molecules (such as cell receptors) or structural components of cell membranes (such as glycoproteins or cholesterol)—should make it possible to recognize activated cells, organs, or pathogenetic states for exact cell and tissue instruction to achieve therapeutic success (Table 3) [4].

General name	Short name	Coating	Applications	Relaxivity	Dcc	Dhb	Clinically approved
Ferumoxide	AMI-25	Dextran	Cell labeling, liver imaging, CNS imaging	r1 = 10.1; r2 = 120	5	120–180	e
Feruglose	NC100150	PEGylated starch	Blood pool agent	n.a.	n.a.	20
Ferumoxsil	AMI-121	Siloxane	Oral GI imaging	r1 = 2; r2 = 47	8.4	300	e
Ferumoxtran	AMI-227	Dextran	CNS imaging, blood pool imaging, cell labeling, macrophage imaging, lymph node imaging	r1 = 9.9; r2 = 65	5.9	15–30
Ferumoxytol	Code7228	Carboxymethyl-dextran	Blood pool agent, cellular labeling, iron replacement therapy in patients with chronic kidney failure, lymph node imaging	r1 = 15; r2 = 89	N.a.	17–31	f
Ferucarbotran	SHU-555A	Carboxydextran	Liver imaging, CNS imaging, cell labeling	r1 = 9.7; r2 = 189	4	62	d

Table 3.

Showing the clinically approved iron oxide nanoparticles examples [42, 53, 54, 55].

3.4 Tissue engineering

The creation of functional replacement tissues or organs using patient cells has been proposed as a therapeutic strategy. These tissues or organs can develop ex vivo (in a bioreactor) for later implantation or in the patient’s body at the site of the defect. It was suggested that nanomagnetic actuation be used as a mechanical simulator in TE and regenerative medicine. Bone TE bioreactors are created employing mechanical actuators made of magnetic nanoparticles. The applications of MNPs in bone tissue engineering can be expanded by the use of an external magnetic field to regulate their movement and operation. An oscillating external field in conjunction with MNPs inside a defect may increase cell induction and remotely send biomechanical cues to the cells to promote osteogenesis (Figure 4) [56, 57, 58].

Figure 4.

Showing mechanism involving cell damage persuade by SPION [56].

3.5 Magnetic particle imaging

SPION mainly used as to detect substance in the magnetic particle imaging (MPI). MPI was announce in 2005, novel pictorial representation method [59]. Generally, the SPION are superparamagnetic. After the action of the magnetic field is turned off, superparamagnetic particle will not remain magnetized. Due to Brownian and Neel relaxation, the magnetization direction can change even at ambient temperature when thermal stimulation occurs. High spatial sensitivity and sensitivity, along with the potential for high-quality real-time imaging, are the benefits of MPI above existing imaging approaches. The spatial bioavailability of the particles affects the MPI approach’s ability to produce high-quality images. Producing tracers with the best magnetically particle spectroscopy (MPS) efficiency is the difficulty of SPION synthesis (Figure 5) [60].

Figure 5.

Showing combination of diagnosis and therapy effect of SPION [52].

4. SPIONs: a better alternative for theranostic agent

The fusion of diagnostics and therapy is known as theranostics or theragnostics, and it can be divided into three types: the simultaneous use of therapeutics and diagnostics, identification followed by therapy, and therapy followed by diagnosis. Theranostics agents are created with the intent of detecting and treating disease at an early stage, monitoring the effectiveness of the therapeutic process, and minimizing time wasted during diagnosis and treatment. Theranostics nanomedicine, also known as nano-theranostics, is based on the aggregation of diagnostic and therapeutic substances into nanocarriers for use in medicine, including liposomes, micelles, carbon nanotubes, nanoparticles, and polymer-based nanomaterials. The imaging component of nanotheranostics relies on the use of fluorescent dyes like quantum dots (for optical imaging), magnetic nanoparticles, such as SPION (for MRI), radionuclides and heavy metals, such as iodine [52]. For the treatment of the diseases, theranostic medicines are used. Theranostic nanomedicine aims to reduce systemic toxicity related to cancer treatment while also improving cancer detection and treatment effectiveness (Figure 6) [52].

Figure 6.

Shows the representation of theranostic system [61].

5. Toxicity of SPION

Studies on the effects of SPION on human and animal cells at the cellular level revealed that SPION can enter cells through passive diffusion as well as endocytosis and have a number of harmful effects by changing gene expression and producing oxidative radicals [62]. Toxic or cytotoxic effects from SPION with altered physicochemical properties are possible. High levels of free ferric ions in that tissue could consequently cause an imbalance in homeostasis and abnormal cellular responses like osmotic damage, cytotoxicity, epigenetic events, DNA damage, and inflammatory disorders, which could result in cancer development or significantly affect subsequent generations [63, 64, 65, 66, 67, 68, 69]. In conclusion, toxicity of SPION, despite being suspected to be low, has not yet been adequately established because human epidemiological studies are almost nonexistent, in vivo studies are scarce, and results from in vitro studies are frequently incongruent. In the field of biomedical applications, a lot of future work has still to be done. For this, the requirement is to understood the interactions and the harmful health consequences of these nanoparticles on cellular system (Figure 7) [71].

Figure 7.

Shows toxic effects of SPION [70].

6. Biosynthesis: an approach to overcome toxicity

One-pot biosynthetic pathway of γ-Fe₂O₃ NPs using natural plant extracts as reducing and capping agents has been promoted in recent years as an easy, affordable, and environmentally friendly substitute for chemical and physical methods of producing nanoparticles. The world economic scientific community is in urgent need of simple, affordable methods to produce ultrasmall (2–20 nm) maghemite nanoparticles using naturally existing plant materials. Single phase γ-Fe₂O₃ NPs can be synthesized by using Ficus carica, Wedelia urticifolia, Plantago major, Pisum sativum, Citrus paradisi, Hibiscus sabdariffa, Ruellia tubercosa as plant extract that shows antioxidant as well as catalytic activity [72, 73]. Magnetite nanoparticles has also been developed using Andean blackberry leaf extract via green synthesis approach. Environmentally friendly and appealing, this straightforward, safe, and inexpensive phytosynthesis of Fe₃O₄ NPs can generate substantial quantities for a variety of nanotechnology applications [74].

7. Conclusion

At the molecular and cellular level, SPION are an alluring platform for cell tracking, tumor diagnosis, and drug delivery owing to their unique magnetic properties and capacity to act as theranostic agents. We have described significant innovations in superparamagnetic Iron Oxide nanoparticles for biomedical applications in this book chapter. Superparamagnetic nanoparticles have been created and synthesized using a variety of chemistry principles. These distinctive structured nanoparticles, such as magneto-core-shell nanoparticles, magneto-micelles, and magnetosomes, promise applications in biomedicine for the detection of bacteria, proteins, and cells as well as benefits for contrast agents and drug delivery. Recent developments in nanotechnology and nanomaterials have led to the development of superparamagnetic nanoparticles with tunable size, morphology, and relaxivity. High r₂ relaxivity, appropriate particle diameters for long circulation, permeation, and immobilization of biomolecules, a narrow size distribution for a uniform response to an external magnetic field, biodegradability and stimuli responsiveness for controlled loading, and r₂ relaxivity are key characteristics that need to be better controlled in future design and development of effective superparamagnetic nanoparticles for biomedical applications. Additionally, establishing a strong structure-pharmacokinetics relationship is likely a crucial aspect of superparamagnetic research and requires additional research evidence. Superparamagnetic nanoparticles may soon be used for disease theranostics in translational medicine once these problems are resolved.

Acknowledgments

Dr. Pramod Kumar would like to sincerely acknowledge the start-up funding (SERB-SRG/2020/000381) provided by the Central University of Himachal Pradesh, India.

Conflict of interest

The authors declare no conflict of interest.

Nomenclature

SPIONs

super paramagnetic iron oxide nanoparticles.

MRI

magnetic resonance imaging.

Dc

core size diameter (nm) determined by laser light scattering.

Dh

hydrodynamic diameter (nm) determined by laser light scattering.

d

only limited countries available.

e

withdrawn from the market.

f

withdrawn from EU market.

RM

regenerative medicine.

TE

tissue engineering.

ROS

reactive oxygen species.