Magnetic Nanomaterials: Applications in Catalysis and Life Sciences: Volume 26 (Smart Materials Series) - Hardcover

Hardcover

ISBN 10: 178262788X ISBN 13: 9781782627883

Publisher: Royal Society of Chemistry, 2017

Synopsis

Details the frontier of magnetic nanotechnology from the persepctive of scientists, engineers and physicians that have shaped this unique and highly collaborative field of research.

About this title

From the Back Cover

Magnetic nanomaterials have undergone a significant evolution during the past decade, with supramolecular nanoparticle organization reaching unprecedented levels of complexity and the materials providing new approaches to treating cancer. Magnetic Nanomaterials will provide a comprehensive overview of the latest research in the area of magnetic nanoparticles and their broad applications in synthesis, catalysis and theranostics.

The book starts with an introduction to magnetism in nanomaterials and magnetic nanoparticle design followed by individual chapters which focus on specific uses. Applications covered include drug delivery, theranostic agents for cancer treatment as well as catalysis, biomass conversion and catalytic enhancement of NMR sensitivity.

The reader will have the opportunity to learn about the frontier of magnetic nanotechnology from scientists that have shaped this unique and highly collaborative field of research. Written and edited by experts working within the field across the world, this book will appeal to students and researched interested in nanotechnology, engineering and physical sciences.

Excerpt. © Reprinted by permission. All rights reserved.

Magnetic Nanomaterials

Applications in Catalysis and Life Sciences

By Stefan H. Bossmann

The Royal Society of Chemistry

Copyright © 2017 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78262-788-3

Contents

Chapter 1 Magnetism in Nanomaterials: Heat and Force from Colloidal Magnetic Particles George Podaru and Viktor Chikan, 1, 
Chapter 2 Magnetic Nanoparticle Design and Application in Magnetic Hyperthermia Andrew Konecny, Jose Covarrubias and Hongwang Wang, 25, 
Chapter 3 Magnetic Nanoparticles in Catalysis Jianming Liu and Wei Sun, 59, 
Chapter 4 Sustainable Magnetic Nanocatalysts in Heterogeneous Catalysis Ayomi S. Perera, 99, 
Chapter 5 Recyclable Magnetic Materials for Biomass Conversion Leidy Peña and Donghai Wang, 120, 
Chapter 6 Catalytic Enhancement of NMR Sensitivity for Advanced Spectroscopic and Imaging Studies in Catalysis and Life Sciences K. V Kovtunov, V V Zhivonitko, I. V Skovpin, O. G. Salnikov and I. V Koptyug, 142, 
Chapter 7 Development of Magnetic Theranostic Agents Asanka S. Yapa and Stefan H. Bossmann, 172, 
Chapter 8 Image-Guided Cancer Thermal Therapies Pegah Faridi, Stefan H. Bossmann and Punit Prakash, 195, 
Chapter 9 Magnetic Nanoformulations for Enhanced Drug Delivery and Retention Aruni P Malalasekera, Stefan H. Bossmann and Gaohong Zhu, 221, 
Chapter 10 Cell-Based Magnetic Nanomaterials for Tracking and Therapy Matthew T. Basel, Tej B. Shrestha and Deryl L. Troyer, 244, 
Subject Index, 261, 

CHAPTER 1

Magnetism in Nanomaterials: Heat and Force from Colloidal Magnetic Particles

GEORGE PODARUa AND VIKTOR CHIKAN

1.1 Introduction

Magnetic materials have fascinated people ever since the development of the first compass in 200-300 BC. In a compass, the earth magnetic field interacts with the lodestone providing information about the direction of the magnetic north pole. This piece of information was crucial to establish a universal navigation system leading to close interaction of various cultures and economies throughout this planet. The magnetic compass has gone through several development stages, but the basic idea remains in today's navigational devices. In nature one finds examples of animals utilizing magnetic nanomaterials for navigation even in the absence of awareness of magnetic fields and magnetic materials. The sensing of the Earth's magnetic field, called magnetoreception, is present in bacteria, arthropods, mollusks, and even in vertebrates. For instance, Magnetotactic bacteria contain several small magnetite crystals that act together as a compass needle to orient these created via very well controlled biomineralization processes to produce single domain magnetite crystals analogous to the artificial colloidal synthesis of magnetic nanomaterials. Humans are thought to be unaware of the Earth's magnetic field, however there are molecules such as cryptochrome that, principally, could serve this purpose. From a thermodynamic perspective, magnetic materials can convert the external energy of a magnetic field into heat or energy/work. The type of interaction depends on the nature of the magnetic field, such as homogeneous, inhomogeneous, static or time dependent (dynamic) magnetic fields. These possible interactions between various types of magnetic fields and materials are listed in Table 1.1 adapted from ref. 3. As one can see there is a wide range of effects on materials in general from the different types of magnetic fields. In this chapter, we will review some basic information about magnetic materials with a focus on colloidal magnetic nanoparticles. We will also focus on how colloidal magnetic nanostructures can produce heat when placed in alternating magnetic fields and how these particles can be used to produce mechanical action, e.g. translational motion in the presence of inhomogeneous magnetic fields, specifically the generation of sound waves and their potential applications.

1.2 Magnetism in Nanoparticles

Magnetic nanoparticles are a group of engineered particles (typically smaller than 150 nm) that can be controlled under the influence of an external magnetic field. In these particles, the magnetic field [??] is produced by magnetic materials or by free electric currents:

[MATHEMATICAL EXPRESSION OMITTED]

µ0 represents the magnetic permeability of a vacuum and the contribution of [??] arises from the generation of a free current while the magnetization [??] can be defined as the induced magnetic dipole moments in a magnetic material. The factors that influence the magnetic properties of nanoparticles include their chemical composition, crystal lattice, particle shape and size, morphology and finally the manner in which the magnetic nanoparticles interact with adjacent particles or with the surrounding matrix. When the size of the nanoparticles decreases, the surface-to-volume ratio increases. Exploring the properties of the large surface-to-volume ratio of the nanoparticles is of critical importance and has led to novel physical, chemical, and mechanical property discoveries compared to those of the corresponding bulk material. For example, Kenneth et al. have shown that reducing the terminal sugar in a dextran coating of iron oxide nanoparticles has had an important impact on the stability of the particles while retaining the same magnetic properties. The magnetic behavior and size dependence of magnetic nanoparticles is controlled by the domain structure of the nanoparticles. The factors that influence the critical size of the single domain consist of the shape of the particles, strength of the crystal anisotropy, value of the magnetic saturation, and domain wall energy. With increasing values of the radius, magnetic nanoparticles can be classified as superparamagnetic, single domain and multi-domain. The domain wall in magnetic particles is important, because it has a major impact on the magnetization of the particles. In general, the magnetic moments of the particles will scale with the volume of the particle, but because of the presence of domain walls, this scaling is abruptly halted when multiple magnetic domains are formed in a single particle. The critical radius (r) represents the point where it is energetically favored for the magnetic particle to exist without a domain wall:

[MATHEMATICAL EXPRESSION OMITTED]

where s represents the magnetic moment per unit mass and Ms2 is the saturation magnetization. In Figure 1.1 it is shown that the coercivity varies dramatically with the particle diameter, unlike the magnetization. In the multi-domain region, it can be observed that the coercivity decreases with the increase of the particle diameter (due to subdivision into domains), while in the single domain region it increases with the radius of the particle. The calculated critical radii for some common magnetic material are: Fe3O4 (4 nm), Co (8 nm), Fe (1 nm) and Ni (35 nm). In other words, a typical colloidal synthetic method is able to produce magnetic nanoparticles that fall into the single domain region. The single domain region can be further divided into two subregions: the superparamagnetic region, where the coercivity is 0 due to the randomizing effects of the thermal energy, and the ferromagnetic region, where the coercivity increases dramatically with the particle diameter. In the absence of a magnetic field, the net magnetic moment is 0 for superparamagnetic nanoparticles, while in an applied magnetic field there will be a net alignment of the magnetic moments. This phenomenon is like paramagnetism with the exception that the magnetic moment originates from a single domain particle (10 atoms) and not from the magnetic moment of a single atom, as observed in paramagnetism. This also means that the saturation magnetization is typically larger in those materials exhibiting paramagnetic behavior.

There are multiple ways in which magnetic nanoparticles can be classified based on their properties. In this chapter, we will concentrate on biological applications. First, magnetic nanoparticles must be biocompatible and non-toxic. Second, the size related properties become important to yield reasonable colloidal and chemical stability. Choosing a versatile magnetic nanoparticle can be very helpful in those cases where the nanoparticle suspension is delivered intravenously, because aggregation (e.g. in blood vessels) must be avoided. For these reasons, in recent years, magnetic nanoparticles have been researched intensively. One solution to this problem has been developed by tailoring their surface chemistry. Recently, Li et al. reported a new synthesis of sodium-citrate-modified iron oxide nanoparticles where the 3T3 cell line maintained a cell viability higher than 70% at medically relevant concentrations.

Regarding diamagnetic shell-enhanced magnetic properties, Ye et al. have shown that mesoporous silica coated superparamagnetic iron oxide nanoparticles exhibited a 21-fold enhanced MRI efficiency when compared to a commercial T contrast agent. A high magnetization value is critical for magnetic nanoparticles, because it will permit control over the movement of particles in blood or lymphatic fluid. Magnetic nanoparticles can be moved closer to a targeted pathological tissue aided by strong magnetic fields. Practically, the desired high magnetization can be obtained by synthesizing nanoparticles that belong to the group of transition metals and their oxides. A list of commonly used magnetic nanoparticles in biomedical applications and their magnetic properties is summarized in Table 1.2. From Table 1.2 one can see the reason why iron oxide is widely used in cancer research. For example, 17 nm iron oxide magnetic nanoparticles have a high saturation magnetization (82 emu g-1), and, at the same time, a high coercivity value (364 G).

1.3 Impact of Static and Dynamic Magnetic Fields on Biological Systems

Natural and human-made magnetic fields permeate our environment. The Earth's magnetic fields typically do not exceed 100 mT, but human-made magnetic fields in medical devices or industrial processes, such as electrolysis or welding machines, do exceed this level. In research facilities, magnetic fields as high as 100 Tesla have become a possibility (the strongest pulsed non-destructive magnetic field produced in a laboratory was at the pulsed Field Facility at the National High Magnetic Field Laboratory's Los Alamos National Laboratory). Magnetic fields will impact not only magnetic materials, but materials that do not show intrinsic magnetism, e.g. water that is a diamagnetic material opposes the magnetic field. The interaction of diamagnetic materials with magnetic fields is typically much less than that of magnetic materials. The magnetic susceptibility of water is small, -0.9 x 10-8 m3 kg-1, in comparison with the susceptibility of typical ferromagnetic materials (100010 000 x 10-1 m3 kg-1). A typical example of the interactions of diamagnetic materials with static magnetic fields is magnetic levitation. For water, the levitation condition is when the magnetic field gradient is around 1400 T2 m-1. For a small "object", such as a frog or a strawberry, this condition is met in a static magnetic field with about 10-20 T. Dynamical magnetic fields can have similar effects on metals. High frequency (10-30 kHz) induction heating is used to magnetically heat and levitate molten metal. Pulsed magnetic fields are known to have an impact on the nerve cells of animals. For instance, Yamaguchi et al. have shown that ventricular defibrillation cannot be attained by a magnetic stimulus with a flux density of 9.2 T or below. Strong magnetic pulses can stimulate biological processes not only at a macroscopic scale, but also at the cellular level. An interesting effect of pulsed magnetic fields (7 T, 2 s) on algae-like fungi (Achlya americana) and protozoans (Saprolegnia diclina) is to open up pores in the lipid bilayers, which can be performed either reversibly or irreversibly. At the molecular scale, magnetic fields can interact with the presence of unpaired electrons in radicals and transition metal complexes, as well as the charges present at the surfaces of larger molecular structures, such as proteins or lipids. It has been shown that the torque on proteins from magnetic fields or magnetic field gradients can positively influence protein crystallization. Magnetic fields can also facilitate the alignment of lipid bilayers. In biological systems, the presence of static and dynamic magnetic fields can contribute to the change in the apparent rates of chemical reactions. The impact of typical dynamic and static magnetic fields are minimal on single reactions. However, in biological systems where there is significant feedback in complex reaction systems, the small impact of the magnetic fields can cause large effects. For instance, small 50 Hz alternating magnetic fields are capable of influencing the free O2 radical concentration in rat lymphocytes in vitro. The European Union has recently surveyed the literature data on the human health effects of RF (low frequency and static electromagnetic radiations). The conclusion of their work is that there is some data available especially at frequencies important for human communication devices. However, there are areas where there is limited data available. Clearly, there is a critical need to further investigate the impact of magnetic fields on biologically important materials at a fundamental level.

1.4 Heating of Magnetic Particles Under the Influence of an External AC Field

It has been observed that when colloidal magnetic nanoparticles are placed in external alternating magnetic fields, the solution can be rapidly heated. The heating takes place by power absorption by the magnetic particles due to the presence of a high frequency alternating magnetic field. The source of power absorption varies with (nano)particle size, as discussed later in this section. In multi-domain particles, the dominant heating is the hysteresis loss due to the movement of domain walls. Although multi-domain magnetic particles were prepared early on, the heating efficacies of these particles are relatively low. The two main contributing mechanisms of SAR (Specific Absorption Rates) in single domain magnetic nanoparticles are Brownian motion (rotation of the entire nanoparticle) and Neel relaxation (random flipping of the spin without rotation of the particle). The transition occurs between 5-40 nm, depending on the materials, but it also varies with frequency and the viscosity of the system. In Table 1.3, calculated transition sizes are shown for typical magnetic NPs in water and in lipids. The latter represent the response in biological media. At low frequencies and larger nanoparticles, Brownian relaxation is the dominant process, while at high frequencies and small nanoparticle sizes Neel relaxation is the main contributor to the heat dissipation. When Brownian relaxation is dominant, the energy from the magnetic field is deposited in a coherent manner (mechanical movement) into the nanoparticles and their surroundings. The important factor for magnetic heating experiments is the specific absorption rate or SAR, which is determined by SAR = C*dTdt-1, where C is the specific heat capacity of the sample and T and t are the temperature and time, respectively. SAR is very sensitive to the materials' properties, which are also dependent on the type and frequency of magnetic field that is applied. Figure 1.2 shows the SAR values of typical magnetic NPs at 100 kHz magnetic field with an amplitude of 5000 A m-1.

The heating capability of magnetic nanoparticles (characterized by their SAR values as shown in Figure 1.2) can be further increased by combining hard and soft magnetic materials at the nanoscale. Magnetic materials in close proximity interact via exchange coupling thus allowing the fine tuning of the magnetocrystalline anisotropy of the combined material. These so-called exchanged coupled magnetic materials provide an increase in SAR values of the NPs by a factor of 5-10. As an example Lee et al. have developed several new exchange coupled systems including CoFe2O4 @MnFe2O4, CoFe2O4 @Fe2O4, MnFe2O4@ CoFe2O4, Fe2O4 @CoFe2O4 and Zn0.4Co0.6 Fe2O4@Zn0.4Mn0.6 Fe2O4. All of these exchange coupled particles exhibit 1000-4000 W g specific loss power compared to the non-exchange coupled constituent of nanoparticles, which are in the range of 100-400 W g-1. The higher heating efficiencies of these materials mean shorter treatment times and smaller required nanoparticle concentrations (fewer potential side effects) in magnetic hyperthermia treatments. The incremental increase of SAR values via various mechanisms could potentially lead to much more viable physical treatment methods that could be used for treating a variety of conditions. In the next paragraph, the impact of the magnetic field types on the heating process will be reviewed.

(Continues...)

Excerpted from Magnetic Nanomaterials by Stefan H. Bossmann. Copyright © 2017 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2017
• Language: English
• ISBN 10: 178262788X
• ISBN 13: 9781782627883
• Binding: Hardcover
• Number of pages: 278
• Editor: Stefan H Bossmann