Functionalized Magnetic Nanoparticles for Theranostic Applications E-Book

• Herausgeber: John Wiley & Sons
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Seitenzahl: 1183

Veröffentlichungsjahr: 2024

Beschreibung

This unique book provides a comprehensive introduction to the multifaceted realm of functionalized magnetic nanoparticles in the field of theranostics, exploring the fundamental concepts, synthesis methods, characterization techniques, and potential applications.

In recent years, the intersection of nanotechnology and medicine has ushered in a new era of therapeutics and diagnostics. Among the myriad nanostructures, magnetic nanoparticles (MNPs) have emerged as versatile candidates with immense potential for theranostic applications. Their unique combination of magnetic properties and functionalization capabilities has paved the way for innovative approaches in both the diagnosis and treatment of various diseases.

Understanding the synthesis, characterization, and manipulation of these MNPs is essential for harnessing their full potential in theranostics. Advances in nanotechnology have enabled precise control over their size, shape, and surface chemistry, allowing for tailored functionalities to suit specific biomedical applications. From superparamagnetic iron oxide nanoparticles (SPIONs) to magnetic nanorods and beyond, the diverse landscape of MNPs offers a rich playground for innovation. The convergence of diagnosis and therapy is facilitated by functionalized MNPs; their magnetic properties render them invaluable tools for imaging modalities such as magnetic resonance imaging (MRI), offering high-resolution anatomical and functional information for disease detection and monitoring. Simultaneously, functionalizing MNPs with targeting ligands, therapeutic agents, or stimuli-responsive moieties empowers them to actively engage in targeted drug delivery, hyperthermia, or magnetic manipulation of biological processes. This synergistic approach exemplifies the essence of theranostics—combining therapy and diagnostics to achieve personalized and precise medical interventions.

The book discusses the challenges ahead, including the translation of functionalized MNPs from bench to bedside, which necessitates rigorous preclinical and clinical evaluations to ensure safety, efficacy, and biocompatibility. Moreover, the complex interplay between nanoparticles and biological systems demands a multidisciplinary approach, bridging the gap between materials science, biology, and clinical medicine. Regulatory hurdles, scalability issues, and ethical considerations further underscore the need for concerted efforts and strategic collaborations in the development and commercialization of MNP-based theranostic platforms.

The readers will find that “Functionalized Magnetic Nanoparticles for Theranostic Applications” comprehensively covers the chemical, structural, and biological properties of functionalized magnetic nanoparticles for theranostic applications as well as most of the challenges.

Audience
This unique reference book will be of great value to materials engineers, polymer scientists, and technologists working in the electronic, electrical, and biomedical industries. It will also be of great use to graduate, postgraduate, and engineering students working in materials and polymer science.

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Functionalized Magnetic Nanoparticles for Theranostic Applications

Edited by

Mayank Pandey

Dept. of Electronics, Kristu Jayanti College, Hennur, Bengaluru, India

Kalim Deshmukh

New Technologies Research Centre, University of West Bohemia, Plzeň, Czech Republic

and

Chaudhery Mustansar Hussain

Dept. of Chemistry & Environmental Sciences, New Jersey Institute of Technology, Newark, New Jersey, United States

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Library of Congress Cataloging-in-Publication Data

ISBN 978-1-394-17240-5

Front cover image courtesy of Adobe FireflyCover design by Russell Richardson

Preface

In recent years, the intersection of nanotechnology and medicine has ushered in a new era of therapeutics and diagnostics. Among the myriad nanostructures, magnetic nanoparticles (MNPs) have emerged as versatile candidates with immense potential for theranostic applications. Their unique combination of magnetic properties and functionalization capabilities has paved the way for innovative approaches in both the diagnosis and treatment of various diseases. This book provides an introduction to the multifaceted realm of functionalized magnetic nanoparticles, exploring their advances, challenges, and the boundless opportunities they present in the field of theranostics.

The exploration of functionalized magnetic nanoparticles begins with an exploration of their fundamental properties. Understanding the synthesis, characterization, and manipulation of these nanoparticles is essential for harnessing their full potential in theranostics. Advances in nanotechnology have enabled precise control over the size, shape, and surface chemistry of MNPs, allowing for tailored functionalities to suit specific biomedical applications. From superparamagnetic iron oxide nanoparticles (SPIONs) to magnetic nanorods and beyond, the diverse landscape of MNPs offers a rich playground for innovation.

As we explore further, we encounter the convergence of diagnosis and therapy facilitated by functionalized MNPs. Their magnetic properties render them invaluable tools for imaging modalities such as magnetic resonance imaging (MRI), offering high-resolution anatomical and functional information for disease detection and monitoring. Simultaneously, the functionalization of MNPs with targeting ligands, therapeutic agents, or stimuli-responsive moieties empowers them to actively engage in targeted drug delivery, hyperthermia, or magnetic manipulation of biological processes. This synergistic approach exemplifies the essence of theranostics—combining therapy and diagnostics to achieve personalized and precise medical interventions.

However, amid the promising advances lie formidable challenges. The translation of functionalized MNPs from bench to bedside necessitates rigorous preclinical and clinical evaluations to ensure safety, efficacy, and biocompatibility. Moreover, the complex interplay between nanoparticles and biological systems demands a multidisciplinary approach, bridging the gap between materials science, biology, and clinical medicine. Regulatory hurdles, scalability issues, and ethical considerations further underscore the need for concerted efforts and strategic collaborations in the development and commercialization of MNP-based theranostic platforms.

This book presents a detailed study of the processes involved in functionalized magnetic nanoparticles for theranostic applications. The basic scientific concepts evolved in functionalized magnetic nanoparticles have attracted researchers worldwide towards their synthesis, properties, and wide range of applications. The comprehensive content of this book covers the existing challenges, as well as the chemical, structural, and biological properties of functionalized magnetic nanoparticles for theranostic applications.

We assure all internationally recognized researchers and authors that this book provides a detailed understanding and novel insights into functionalized magnetic nanoparticles, their performance, properties, and biomedical applications. In response to the needs of the present generation, researchers, academics, and industrialists are increasingly interested in functionalized magnetic nanoparticles. This book will be extremely useful and valuable for all readers working in the field of theranostic and biomedical applications. It will also help to understand and address the fundamental limitations associated with the research field. The wide range of topics covering all dimensions will serve as an excellent reference source for young researchers to gain expertise in this particular area.

The editors are grateful to all the contributing authors for their hard work and excellent research contributions to this book. The editors also thank Martin Scrivener and Scrivener Publishing for their support and publication.

Dr. Mayank Pandey

Dr. Kalim Deshmukh

Dr. Chaudhery Mustansar Hussain

1Magnetic Nanoparticles: Classifications, Structure, Physicochemical Properties, and Implications for Biomedical Applications

Ezaz Haider Gilani1, Umer Mehmood2, Rabia Nazar2*, Andleeb Arshad2, Faris Baig2, Arshia Fatima2, Noor Shahzadi2, Usama Mehmood2 and Fahad Iftikhar2

1School of Chemistry, Minhaj University Lahore, Pakistan, Lahore, Punjab, Pakistan

2Polymer and Process Engineering (PPE) Department, University of Engineering and Technology (UET) Lahore, Pakistan, Lahore, Punjab, Pakistan

Abstract

Magnetic nanoparticles (MNPs) are a progressively new type of nanoparticle (NP) that is strongly influenced by magnetic fields. These particles typically have two parts: a magnetic component, which is frequently composed of iron, nickel, or cobalt, and a reducing/capping component. Nanoparticles typically have a diameter of less than 1 m (between 1 and 100 nm), whereas the diameter of larger microbeads ranges from 0.5 to 500 m. Magnetic nanoparticle clusters, which are composed of multiple separate magnetic nanoparticles with diameters ranging from 50 to 200 nm, are also referred to as magnetic nanoparticle beads. The foundation for the subsequent magnetic nanochains consists of magnetic nanoparticle clusters. Due to the potential use of MNPs in a variety of industries, such as catalysis, magnetically adjustable colloidal photonic crystals, biomedicine, tissue-specific targeting, storage devices, cleanup of the environment, nanofluids, nano solutions, optical filters, sensors, magnetic cooling, and cation sensing, magnetic nanoparticle research has received much attention in recent years.

Compared to other nanostructures, MNPs are considered the most significant and often employed class of nanomaterials. These particles have several applications. However, their intrinsic magnetism makes several tasks easier, such as targeting, which is crucial and required in medication delivery, making them significant in biomedicine, particularly in the area of drug delivery. The objectives of this chapter are to gather and provide general precise data and information on MNPs and the characteristics of these particles in biomedical applications. The features of these particles and their numerous uses in medication delivery are discussed in the following sections. Furthermore, a fundamental consideration for coating magnetic nanoparticles was made. It has also been noted that the coating of MNPs is mandatory for medical purposes. The process of loading pharmaceuticals onto MNPs, entry into the body, targeting, and release of drugs are important aspects of the biomedical applications of MNPs. A brief explanation is provided to address the current issues and the stability of MNPs.

Keywords: Magnetic nanoparticles, nanoparticle classification, biomedical applications, physicochemical properties, nanoparticle structure, magnetic resonance imaging (MRI), drug delivery, nanomedicine

List of Abbreviations

MNPs

Magnetic Nanoparticles

NPs

Nanoparticles

MRI

Magnetic Resonance Imaging

IONPs

Iron Oxide Nanoparticles

FeO

Iron Oxide

PCR

Polymerase Chain Reaction

FeCl

3

Iron Chloride

CTAB

Cetyl trimethyl ammonium bromide

HAuCl

4

Gold chloric acid

TEOS

Tetra ethoxy silane

CVD

Chemical Vapor deposition

MCE

Magneto-caloric effect

CoPt

3

Cobalt platinate

FePt

Iron Platinum

Co(CO)

5

Cobalt Penta carbonyl

Co-NPs

Cobalt Nanoparticles

TEM

Transmittance Emission Spectroscopy

SEM

Scanning Electron Microscopy

XRD

X-ray Diffraction

H

Hours

PPE

Personal Protective Equipment

1.1 Introduction

For decades, MNPs have been used in diagnostic applications. MNPs are extremely promising because of their high magnetism, surface area, volume ratio, dispersibility, propensity to interact with different molecules, and superparamagnetic characteristics. They have been used in numerous medical fields, most notably in magnetic resonance imaging (MRI). Frequently used iron and its oxide (FeO) nanoparticles (IONPs) exhibit low toxicity and excellent superparamagnetic characteristics. However, IONPs face numerous obstacles, which make it difficult for them to enter the market. To overcome these difficulties, research has focused on creating MNPs with improved magnetic characteristics and safety profiles. Doping MNPs (especially IONPs) with other metallic elements (such as cobalt and manganese) reduces the amount of iron (Fe) released into the body and results in the production of multimodal nanoparticles with distinctive features. Another strategy entails creating MNPs from metals other than Fe that have excellent magnetic or other imaging properties. The development of MNPs, which can also be used as multipurpose platforms to combine various MRI applications or biomedical imaging techniques to create more accurate and comprehensive diagnostic tests, appears to be the future direction of the field.

Disease diagnosis is the first step toward effective therapy. To accurately determine a patient’s current state and how they may develop in the future, it is crucial to establish their complete medical and family history, calculated risk factors, and symptoms (or lack thereof). This information must be cross-checked with the results of the diagnostic testing. However, the prognosis of a patient is significantly influenced by the stage at which the disease is identified. The fact that many crucial disorders are detected at very late stages is one of the main causes of “avoidable fatalities.” The most common example of this is cancer. According to a 2009 study, many cancer deaths that could have been prevented were caused by delayed diagnosis and potentially curative therapies [1]. Additionally, Virnig et al. released a study in the same year, examining the differences in cancer survival rates between White and African Americans in United States (USA). Overall, African Americans were less likely to survive for more than five years after diagnosis and were more likely to receive a late-stage cancer diagnosis [2]. The same logic holds true for the treatment of infectious disorders; identifying the pathogen responsible for the infection enables the choice of the most suitable therapeutic with the lowest risk of developing antibiotic resistance [3, 4]. The list of instances is endless and encompasses all medical specialties; in modern times, an early diagnosis is frequently associated with a favorable prognosis [5]. The lack of appropriate diagnostic tools and assays is a significant contributor to the delayed diagnosis. An example of a diagnostic test with a high resolution and deeper tissue penetration is MRI. High sensitivity and specificity are disappointingly poor [6]. Polymerase Chain Reaction (PCR) tests, on the other hand, are very sensitive and specific assays, but their turnaround time is too long [7]. To the issues mentioned, magnetic nanoparticles (MNPs) appear as promising remedies. They are potential technologies in the field of molecular diagnosis that can be used to create diagnostic tests that are quicker, easier, and less expensive using magnetic separation techniques. MNPs can also be used in MRI to increase sensitivity and specificity. They have been investigated as diagnostic tools for many years, and as early as 1993, several MRI contrast agent compositions have received regulatory approval [8].

In recent years, numerous efforts have been made to manufacture and create magnetic nanoparticles (MNPs) for different industries and fields, such as biotechnology, drug delivery systems, and computers. In general, the optimal design and production of these nanoparticles affect how well they work and are used. Numerous magnetic nanoparticles have been created thus far, including ferrites (MFe2O4, where M = Metal), pure metallic NPs, metal oxide NPs, alloys, and bimetallic NPs [6, 9]. The creation of magnetic nanoparticles must consider some important factors, including their intrinsic magnetic characteristics, size, shape, surface coating, surface charge [10, 11], stability in aqueous media, and non-toxicity [12, 13]. Different parameters (size, shape, surface area, coating, and stability) of MNPs can be regulated by selecting an appropriate synthesis process [14–16]. Iron oxides typically play a significant impact in the selection of magnetic material [17–19]. These oxides have remarkable stability against degradation, and in contrast to other magnetic nanoparticles, exhibit good magnetic characteristics [12, 13, 20, 21]. In addition, these nanoparticles are less hazardous. To date, several techniques have been put out and improved upon for the production of MNPS. Magnetic particles have received considerable attention in this investigation because of their distinctive characteristics [22–29]. A few decades ago, there was an increase in the chemical synthesis of nanomaterials and the surface modification of materials. These processes are employed in numerous fields, such as biomedicine, biotechnology, catalysis, magnetic chemistry, and thermoelectric materials. The manufacturing of MNPs with adjustable size, distribution, and surface modification has been achieved using different methods and techniques [30–32]. In these procedures, either bottom-up or top-down processes are used to manufacture MNPs using various techniques, including microwave, ultrasonication, vapor deposition, electrochemical, and microwave methods. These two methods are typically used to create nanoparticles with magnetic properties. Magnetic nanomaterials have numerous applications in a variety of disciplines, including biology, medicine, and engineering [33, 34]. This chapter presents the most recent advancements in the architecture, occurrences, most popular samples, and areas of application of MNPs.

1.2 Synthesis Methods of Magnetic Nanoparticles (MNPs)

1.2.1 Synthesis in Liquid Phase

Precipitation methods, microemulsion techniques, ultrasound, sonication tools, and other processes have been used to create MNPs in liquid media [12, 13, 15]. The LaMer principles and diagrams can be used to justify the homogeneous production of highly uniform particles (monodisperse). The penetration of MNPs on the surfaces of already-prepared nuclei and irreversible building of magnetic nuclei is the cause of particle growth.

1.2.1.1 Co-Precipitation

The co-precipitation synthesis technique is the least complicated and effective way to chemically create MNPs [35]. The co-ability of precipitations to synthesize many NPs is a key benefit. However, this approach has a limited ability to control particle size distribution, and particle development is controlled by kinetic factors [36]. The co-precipitation approach is depicted schematically in Figure 1.1; it involves first preparing a solution of iron ions in HCl, which is then added to a solution of diisopropylamine (DIPA), resulting in the precipitation of FeO NPs [11, 37].

Figure 1.1 Schematic diagram of co-precipitation method.

1.2.1.2 Arc Discharge

This process is frequently used to create MNPs consisting of metal carbides or nanoparticles encased in a carbon layer (carbon encapsulated). This technique uses arc discharge to evaporate the metal, which is positioned on a graphite electrode [38]. Using this technique, boron nitride can also be applied to the surfaces of metal NPs. Unfortunately, this technology cannot be applied on an industrial scale because of drawbacks, such as low efficiency and difficulties in controlling the size and thickness of the produced NPs. In addition to these techniques, NPs with sizes less than 10 nm can also be created using laser light [39–41].

1.2.2 Thermal Decomposition (Non-Aqueous Media Synthesis)

There are known methods for creating magnetic particles with controlled shape and size. These methods take cues from high-quality semiconductor oxides and nanocrystals that were created in non-aqueous media through thermal breakdown [42, 43]. Essentially, smaller monodisperse magnetic nanocrystals can be created by thermally decomposing organometallic compounds to stabilize surfactant-containing high-boiling organic solvents, as shown in Figure 1.2 [44–46].

Metal acetylacetonates, metal cupferrons, and carbonyls are examples of organometallic precursors [47]. Oleic acid, hexadecylamine, and fatty acids are frequently used as surfactants. In general, the ratio of the initial reagents (metallic compounds, surfactants, and solvents) is the key variable in determining the size and shape of the magnetic nanoparticles. Precise regulation of the size and morphology, reaction temperature, and time may also be essential. Zerovalent metal precursors, as in the case of carbonyls, initially cause the metal to form by heat breakdown, but multi-step processes are also employed to create nanoparticle oxides. When trimethylamine oxide, a mild oxidant, is added to a solution of octyl ether and oleic acid at a temperature of 100 °C, Fe pentacarbonyl, for instance, can break down, forming monodisperse g-Fe2O3 nanocrystals that are approximately 13 nm in size as shown in Figure 1.3[48]. When precursors containing cationic centers disintegrate in the presence of 1,2-diaminopropane, the result is oxides, specifically Fe3O4, if [Fe(acac)3] is degraded in phenol ether and 1,2-hexadecanediol, oleylamine, and oleic acid [45]. Peng et al. reported the synthesis of magnetic oxide nanocrystals with controlled sizes and shapes by pyrolysis of metal fatty acid salts in a non-aqueous solution [49]. The reaction system commonly includes a hydrocarbon solvent or a combination of octadecene and tetracosane and the appropriate fatty acids. In addition, it was possible to create nearly monodisperse Fe3O4 nanocrystals with controllable forms, including dots and cubes; the sizes were adjustable over a size range (3–50 nm).

Figure 1.2 Schematic diagram of thermal decomposition.

Figure 1.3 TEM images of Fe3O4 nano-crystals synthesis [48].

Reproduced with the permission of American Chemical Society. Copyright © 2001.

Magnetic nanocrystals (Cr2O3, MnO, Co3O4, and NiO) were successfully synthesized using this generalized approach. Variations in the reactivity and concentration of the precursors can be used to alter the morphology of nanocrystals. Activity was modified by adjusting the chain length and fatty acid concentration. In general, the response rate increased with a decrease in the chain length. The reaction temperature could be lowered, and the reaction rate could be increased by using alcohols or primary amines. Similar thermal breakdown techniques were employed by Hyeon et al.[44] to create monodisperse FeO-NPs. They produced in situ iron oleate complexes using non-toxic, affordable FeCl and Na-oleate, which were subsequently broken down at temperatures ranging from 240 to 3,208 °C in a number of solvents. Depending on the temperature and time of breakdown, the particle sizes ranged from 5 to 22 nm. In this synthesis, it was discovered that aging was required for the development of FeO-NPs. Hexane and toluene are two examples of organic solvents in which the produced nanoparticles can be dispersed. However, whether the particles can be disseminated in water is unknown. The same research group discovered that monodisperse iron nanoparticles (6–15 nm) could be formed because of the decomposition of Fe(CO)5 and the Fe-oleate complex at various temperatures. The total procedure resembles seed-mediated growth, which is explicable by the traditional LaMer mechanism: nucleation and growth are completely separated after transient nucleation from a supersaturated solution followed by sluggish growth of particles with little to no subsequent nucleation. In Hyeon’s synthesis, growth is induced by the Fe-oleate complex’s thermal decomposition at higher temperatures, whereas nucleation is induced by the thermal decomposition of Fe(CO)5 at low temperatures [50]. The nanoparticles discussed above can be dissolved in an organic liquid. However, water-soluble MNPs are preferred for use in biotechnology. Recently, remarkably straightforward production of water-soluble MNPs has been described. Water-soluble Fe3O4 nanocrystals were prepared using FeCl3·6H2O and 2-pyrrolidone under reflux (245 °C) [51]. When the reflux period was 1, 10, or 24 h, the average size was regulated at 4, 12, and 60 nm, respectively. The forms of the particles varied with increasing reflux time, transitioning from early spherical to later cubic morphologies. Subsequently, the same research group created a one-pot method for producing water-soluble MNPs under identical reaction conditions by adding a capping agent with a dicarboxylic end to poly(ethylene glycol) [52]. These NPs may be employed as contrast agents in MRI to help detect malignancies.

Metallic NPs were also prepared using a thermal decomposition technique. The advantage of MNPs over metal oxides is their higher magnetization, which is particularly intriguing in data storage media. Metallic Fe-NPs were created by thermally breaking down [Fe(CO)5] in poly-isobutene under a N2 environment at 170 °C [53]. Depending on the Fe(CO)5/polyisobutene ratio, the particle size can be varied between 2 and 10 nm (polydispersity of approximately 10%). The polymer surrounding the Fe-NPs was roughly 7.0 nm thick. However, susceptibility studieshave shown that these iron particles can still be quickly oxidized in air. As a result, the particle size slightly increased by a factor of approximately 1.3. Chaudret et al. reported the synthesis of iron nano cubes by decomposing [FeN[Si(CH3)3] with H2 in hexadecylamine, oleic acid, or hexadecyl NH3Cl at 150 °C [54]. The dimensions of the nanocubes can be changed from 7 to 8.3 nm having interparticle spaces varying from 1.6 to 2 nm, by altering the amounts of amine and acid ligands. With their crystallographic axes aligned, these nanocubes could be joined into extended crystalline superlattices. The size and shape of cobalt nanoparticles can be adjusted using the thermal decomposition technique [55]. Cobalt nanodisks were created according to Alivisatos et al. by thermally decomposing a co-carbonyl [49, 56]. The creation of nickel and cobalt nanorods via the high-temperature reduction of a non-carbonyl organometallic unit was reported by Chaudret et al. For example, the disintegration of [Co(h3-C8H13) (h4-C8H12)] under H2 in anisole at 150 °C in a mixture of hexadecylamine and fatty acids (lauric acid, octanoic acid, and stearic acid) led to the synthesis of monodisperse ferromagnetic cobalt nanorods. Using various acids, the diameter and length of the co-nanorods can be changed (Figure 1.4) [57].

Magnetic nanoparticles that are air stable are particularly appealing because they are simple to manage and can be used in oxidizing environments. The thermolysis of [Co2(CO)8] in aluminum alkyl produced air-stable, “monodisperse” colloidal Co-NPs, Diameters of Co NPs can be adjusted from 3 to 11 nm by adjusting the chain length of the organoaluminum compounds. It was discovered that obtaining air-stable cobalt nanoparticles is required and depends on moderate surface oxidation with synthetic air. Without this oxidation step, after peptization with the surfactant KorantinSH, the magnetization of the Co0 particles degraded quickly in air. Magnetic alloys have numerous benefits such as high magnetic anisotropy, improved magnetic susceptibility, and high coercivities [58]. Metal phosphides, in addition to CoPt3 and FePt, [59, 60] are currently of scientific interest in chemistry and materials sciences [61, 62]. For example, the ferromagnetism, magnetoresistance, and magnetocaloric properties of hexagonal Fe phosphides and have been thoroughly investigated [63, 64]. Brock and colleagues recently created FeP and MnP NPs using high-temperature reactions of tris(trimethylsilyl)phosphane with Fe-acetylacetonate and Mg-CO [65]. Antiferromagnetic FeP nanorods were recently created through the thermal breakdown of a precursor combination solution [66]. Additionally, individual iron phosphide (Fe2P) nanorods were produced using a syringe pump to thermally decompose Fe(CO)5 in trioctyl, phosphane [67].

Figure 1.4 TEM images representing the formation of cobalt nanorods [57].

Reproduced with the permission of Wiley. Copyright © 2003.

1.2.3 Microemulsion

In an emulsion, the anisotropy and thermally stable dispersion of liquids and the surface coating of micelles stabilize the microdomain of either one or both of the immiscible liquids [68]. The size of the aqueous droplets in water-in-oil emulsions varies from 1 to 50 nm, and they are encircled by a monolayer of micelles in the continuous hydrocarbon phase. The molar ratio of H20 to the surfactant affects the size of the micelle [69]. The required reactants can be utilized to create identical water-in-oil micelles, causing the microdroplets to repeatedly collide, group, and shatter before a precipitate forms in the micelles [70]. Precipitates are eliminated by filtration or centrifugation of the liquid in solvents, such as acetone or ethanol. The use of an emulsion as a nanoreactor to produce nanoparticles is possible. The microemulsion technique has been used to create cobalt/platinum alloys, gold-coated Co/Pt NPs, and metallic Co in reverse micelles of cetyltrimethylammonium bromide, with 1-butanol as a co-surfactant and octane as oil droplets [71]. The most important magnetic material, MFe2O4, has been extensively utilized in electronic applications. Inverse micelles and microemulsions can be used to prepare spinel ferrite. For instance, using sodium dodecyl benzene sulfonate (Na-DBS) as a surfactant, water-in-toluene inverse micelles were formed to create MnFe2O4 NPs with controlled diameters ranging from approximately 4 to 15 nm [72]. Mn(NO3)2 and Fe(NO3)3 were dissolved in a transparent aqueous solution as the initial components of the synthesis. To create reverse micelles, toluene was incorporated into a mixture of metallic saline and Na-DBS aqueous solutions. The diameter of the resultant MnFe2O4 NPs depended on the volume fraction of toluene and water. In reverse micelles made from oleic and benzyl ether, Woo et al. showed how iron oxide nanorods can be prepared using the sol–gel method, with propylene oxide acting as a proton scavenger and FeCl3·6H2O as an iron supply [73]. Reflux or heating in tetralin can be used to alter the rex temperature, environment, and hydration of gels, which can be utilized to control the nanorods’ phase. Methylamine was utilized to synthesize a CoFe fluid from the in situ formed Co and Fe-dodecyl sulfate, which was produced by mixing an aqueous solution of Na-dodecyl sulfate and either FeCl or Co-acetate solution [74]. The size of the Co-ferrite NPs decreases with a decrease in the total reactants and an increase in the amount of sodium dodecyl sulfuric acid. The typical particle size ranges from 2 to 5 nm. However, between 30 and 35%, the polydispersity was very significant. The microemulsion method can produce nanoparticles that are spheroids or tubes, or even have an oblong cross-section [75]. Although numerous different variations have been produced under controlled conditions using emulsion processes, the particle size and shape of magnetic nanoparticles often vary across a very wide range. Additionally, the yield of nanoparticles produced by microemulsion synthesis is often poor compared with thermal breakdown and coprecipitation. A large amount of solvent is required to synthesize a significant amount of material. As a result, this method is not very effective and is difficult to scale up. A generalized hydrothermal approach for the liquid–solid–solution reaction of a range of unique nanocrystals was published by Li et al. A metal linoleate, ethanol, linoleic acid, and a solution of water and ethanol at various reaction temperatures constitute the system under hydrothermal conditions [76]. This approach, which is based on generic phase transfer and sources that occur at the surfaces of liquid, solid, and solution phases that are involved during synthesis, can provide very homogeneous Fe3O4 and CoFe2O4 nanoparticles. These nanoparticles were approximately 9–12 nm in diameter, as shown in Figure 1.5. Li et al. reported the hydrothermal decline production of monodisperse, hydrophilic, and single-crystalline ferrite microspheres [77]. FeCl3, ethylene glycol, sodium acetate, and polyethylene glycol were mixed immediately to form a clear solution. The mixture was then enclosed in a stainless-steel autoclave that had been lined with Teflon and heated to 200 °C, where it was maintained for 8 to 72 h. Ferrite spheres with a narrow size distribution and tweakable diameters in the 200–800 nm range were produced using this technique. Li et al. expertly guided the multicomponent reaction mixtures that included polyethylene glycol, sodium acetate, and ethylene glycol. The multicomponent technique seems to be useful in controlling the synthesis of desirable materials, although the mechanism is not yet completely understood. The preferred synthesis process is co-precipitation, which is the most straightforward process. Thermal breakdown is currently the most effective method under investigation for regulating the size and shape of NPs.

Figure 1.5 (a) TEM images of nanocrystals, and (b) LSS phase transfer synthetic strategy [76].

Reproduced with the permission of Springer Nature. Copyright © 2005.

Alternatives to particle agglomeration include nanoparticles, polyethylene glycol as a stabilizer to prevent the agglomeration of nanoparticles, and sodium acetate as an electrical stabilizer. The multicomponent approach is effective for controlling the production of desirable minerals. The preferred synthesis process is co-precipitation since it is the most straightforward. Thermal breakdown appears to be the most effective method under development right now for regulating the size and shape of NPs. Additionally, nanoparticles with narrow size distributions and different morphologies can be created using microemulsions. A considerable amount of solvent was required in this approach. Hydrothermal synthesis is a technique that has not been widely investigated for the creation of MNPs, even though it can provide high-quality nanoparticles. Magnetic nanoparticles are created through co-precipitation, and thermal breakdown has received the most scientific attention to date. The stability of MNPs created by these processes is brought about either by steric hindrance or electrostatic repulsion, depending on the stabilizers used (fatty acids or amines) and the polarity of the solvent utilized. Electrostatic forces preserve the positively charged magnetite nanoparticles formed during co-precipitation [78]. However, nanoparticles produced by thermal breakdown in an organic solvent are often sterically stabilized by fatty acids or surfactants [45].

1.2.4 Green Synthesis of NPs