Novel Nanomaterials for Biomedical, Environmental and Energy Applications

By Xi Chen

Novel Nanomaterials for Biomedical, Environmental, and Energy Applications is a comprehensive study on the cutting-edge progress in the synthesis and characterization of novel nanomaterials and their subsequent advances and uses in biomedical, environmental and energy applications. Covering novel concepts and key points of interest, this book explores the frontier applications of nanomaterials. Chapters discuss the overall progress of novel nanomaterial applications in the biomedical, environmental and energy fields, introduce the synthesis, characterization, properties and applications of novel nanomaterials, discuss biomedical applications, and cover the electrocatalytical and photothermal effects of novel nanomaterials for efficient energy applications.

The book will be invaluable to academic researchers and biomedical clinicians working with nanomaterials.

• Offers comprehensive details on novel and emerging nanomaterials
• Presents a comprehensive view of new and emerging tactics for the synthesis of efficient nanomaterials
• Describes and monitors the functions of applications of new and emerging nanomaterials in the biomedical, environmental and energy fields

• Language: English
• Publisher: Elsevier Science
• Release date: Nov 16, 2018
• ISBN: 9780128144985

Book preview

China

Preface

Xiaoru Wang ; Xi Chen

Over the past decade, the development and applications of nanomaterials has been pursued with great interest by many researchers and has shown a tremendous potential growth in the energy, environmental, and biomedical fields. These studies and applications require interdisciplinary synergism in physical, chemical, and biological fronts. Compared with their bulk materials, novel nanomaterials indicate more excellent characteristics and are widely applied for biomedical diagnosis, bioimaging, analytic sensing, air pollution control, and efficient energy generation and storage. In an attempt to disseminate the growth of novel nanomaterials in the abovementioned application areas, this book reviews and highlights the recent progress and the latest findings of a wide range of nanomaterials, including metallic and noble metal nanomaterials; carbon-based nanomaterials; and various types of quantum dots such as carbon nanotubes, graphene quantum dot (GQD), graphitic carbon nitride (g-C3N4) nanosheets, and magnetic nanomaterials.

With an insight to future trends in the ever-growing field, this book summarizes the developments of several typical novel nanomaterials over the past decade. Chapter 1 reviews the overall progress of novel nanomaterial applications in the biomedical, environmental, and energy fields. The development of the synthesis, characterization, properties, and applications of novel nanomaterials are introduced in a tutorial fashion for nontechnical specialists. Chapter 2 deals with the protein analysis using some novel nanomaterials with various compositions, morphologies, and proper surface area credited to their advantages such as specificity and sensitivity detection, short assay time, high-throughput capability, and low sample consumption. Chapter 3 discusses the use and syntheses of magnetic nanomaterials to analyze biomolecules and cells based on magnetic effects. As the surface functionalization of nanomaterials greatly improves their optical, electric, and magnetic properties, the applications of nanomaterials are obviously expanded. Chapters 4–7 cope with aspects of the DNA analysis using the functionalization of gold nanoparticles; the recent developments in functionalizing carbon nanodots toward bioimaging and biosensing applications; and the determination of metal ions in aqueous solution using fluorescent GQDs with raw, doped, or surface functionalization. Then, the design of optical nanosensors for sensing and imaging intracellular pH is discussed, and the perspective of nanomaterials for intracellular pH sensing and imaging is given in Chapter 8. Aspects of nanomaterials including plasmonic metallic nanomaterials used as gas biosensors, optical biosensors, or chemobiosensors for air pollution control and their applications on air purification are also discussed in several chapters as required, which provide the application information on environmental fields. Furthermore, Chapters 13 and 14 cover the electrocatalytic and photothermal effects for efficient energy applications of novel nanomaterials.

The latest application progress for novel nanomaterials in biomedical, environmental, and energy is summarized in this book for a broader readership including college students and academic researchers in energy, biomedical, and environmental fields. Thus, the topics presented in this book are wide ranging and somewhat diverse. But all contributions focus on the diagnostics type of analytic systems, and the information provided has been explained in a straightforward fashion, making the contents easily comprehensible for the targeted readers. All authors are experts in their fields and are authoritative in their respective chapters. The editors would like to express their sincere appreciation to all authors for their efforts in preparing excellent contributions. Their efforts and cooperation enabled the book to be completed in time.

Chapter 1

Introduction

Zhixiong Cai⁎; Feiming Li⁎; Mingcong Rong†; Liping Lin§; Qiuhong Yao‡; Yipeng Huang⁎; Xi Chen⁎; Xiaoru Wang‡    ⁎ Department of Chemistry and MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China

† School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou, China

‡ Department of Analytical Science and Technology, Xiamen Huaxia University, Xiamen, China

§ College of Life Sciences, Fujian Agriculture and Forestry University, Fuzhou, China

Abstract

Nanomaterials are emerging extraordinary zero- and two-dimensional materials. They are derived from bulk materials or self-assembled from micromolecules. The most intuitive way to observe the changes of nanomaterials is by microscopes, especially those ultrasensitive ones, such as scanning electron microscope, transmission electron microscope, confocal fluorescence microscope, scanning tunneling microscope, and atomic force microscope. Nanomaterials possess typical optical and electric properties, which can be detected by fluorescence spectrophotometer, Raman spectrometer, and electrochemical workstation. In this chapter, classic synthesis methods and typical characterization of novel nanomaterials were summarized. Recent progress in the synthesis and characterization of novel nanomaterials and our fundamental understanding of their properties has led to significant advances in biomedical, environmental, and energy applications. Furthermore, their applications in biomedical diagnosis of cancer, bioimaging, air pollution control, and efficient energy generation and storage are thoroughly introduced and discussed in detail.

Keywords

Nanomaterials; Characterization; Optical and electric properties; Natural nanomaterials; Toxicity of nanomaterials; Environmental; Energy

Synthesis of Novel Nanoparticles

Nanomaterials are materials that are at least one dimension in nanoscale (0.1–100 nm) or as a basic unit in a three-dimensional space, showing more excellent properties or some special properties compared with their bulk materials, such as optics, magnetism, and electric and catalytic properties, and have been widely applied for analytic sensing, bioimaging, energy storage, catalyst, and so on. Hence, nanoparticles have boost great scientist great interest, and they have paid great efforts to develop a series of methods to synthesize novel nanomaterials, such as noble metal nanoparticles, quantum dots, upconversion nanoparticles, metal oxide nanoparticles, carbon nanomaterials, and two-dimensional nanomaterials. This section will mainly give an introduction of novel nanoparticle synthesis methods, which mainly focus on the bottom-up methods.

Bottom-up approaches include the miniaturization of material components (up to atomic level) with further self-assembly process leading to the formation of nanostructures. During self-assembly, the physical forces operating at nanoscale are used to combine basic units into larger stable structures. To be specific, bottom-up approach refers to the buildup of a material from the bottom: atom by atom and molecule by molecule. Atom by atom results in the formation of self-assembly of atoms/molecules and clusters. These clusters come together to form self-assembled clusters into nanoparticles. Typical examples are quantum dot formation during epitaxial growth and the formation of nanoparticles from colloidal dispersion.

Physical Methods

Physical methods of bottom-up approaches start with atoms or molecules and buildup to nanostructures, including atomic layer deposition, vacuum arc process, chemical vapor deposition, sputter deposition, electric arc deposition, and laser ablation. The inert gas condensation process is one of the most known and simplest techniques for the production of 0-D nanomaterials. For instance, fullerenes with various geometry are generated from an inert gas source [1]. Besides, there are lots of methods to fabricate nanostructures by evaporating the materials on different substrates. The nanostructured materials can be in the form of thin films, multilayer films, or nanoparticulate thin films (thin films composed of nanoparticles). Moreover, there are several methods in which material of interest is brought in the gaseous phase (atoms or molecules) that can form clusters and then deposit on appropriate substrates. Chemical vapor deposition methods have been adapted to make 1-D nanotubes (carbon nanotubes) and nanowires, using catalyst nanoparticles to promote nucleation and ultrathin 2-D nanomaterials (such as graphene and transition metal dichalcogenides (TMDs) MoS2, WS2, [2] etc.) with high crystal quality, high purity, and limited defects on certain substrates.

Chemical Methods

Among the methods for the fabrication of nanomaterials, chemical methods have been widely investigated because the involved instrumentation is simple and cost-effective compared with most of physical methods. In most cases, nanomaterials could be obtained as colloidal particles in solutions and can be dried to obtain powders. Zero-, one-, two-, and three-dimensional nanomaterials of different shapes and sizes are possible depending upon the chemicals used and reaction conditions. In the past several decades, scientists devote to understanding the process of atom-by-atom nucleation and growth of small-to-large particles and then to special dimension in melts, aqueous or nonaqueous media from gas phase, or even in solids. The process of nucleation is a bottom-up approach in which atoms and/or molecules come together to form a solid. The process can be spontaneous, and it may be homogenous or heterogeneous nucleation. Here, we mainly focus on some three strategies: hydrothermal and solvothermal methods, sonochemical synthesis (microwave and ultrasound method), and hot-injection method.

Hydrothermal and solvothermal method

Hydrothermal and solvothermal methods are useful to produce nano- to microparticles in large scale. In these techniques, adequate chemical precursors are dissolved solvent and placed in vessel made of steel or any other suitable metal that can withstand high temperature typically up to 300°C for hydrothermal and 600°C for solvothermal method and high pressure above 100 bar. The techniques become useful when it is difficult to dissolve precursors at low temperatures. It is also beneficial to synthesize nanoparticles if the materials have a high vapor pressure near their melting points or crystalline phases that are not stable at melting point. The uniformity of shapes and sizes of the nanoparticles also can be achieved by these methods [3–6].

Sonochemical synthesis

Microwave method

Conventional heating approaches mainly consist of electric heating, sand baths, oil baths, and heating jackets. Great efforts have been paid during the past decade to develop alternative energy sources by considering working efficiency, environmental friendliness, and energy consumption. Microwave method consists of an electromagnetic radiation and lies between radio waves and infrared frequencies, and relative wavelength spans from 1 mm to 1 m. Dipole rotation and ionic conduction are the two fundamental mechanisms for transferring energy from microwave methods to the substance being heated. Microwave methods heating normally can be carried out through the interaction of electromagnetic radiation with the dipole moment of the molecules, whereas dipole moments rotate to align themselves with the alternating electric field of the microwave methods. Therefore, water or ionic liquids with a high dipole moment are considered to be the best solvents for use in microwave method-based syntheses [7,8].

Ultraound in chemistry

Ultrasound irradiation is one of the most powerful techniques that benefit of its simple operation under ambient conditions, product selectivity, and reduced reaction times. Recently, the use of ultrasound irradiation in chemistry, that is, sonochemistry, has grown significantly, resulting in a considerable part of empirical research. In this technique, the reactant molecules undergo chemical reactions due to the application of powerful ultrasound waves (20 kHz to 1 MHz). The sonochemical method in liquids is an acoustic cavitation process, which consists of the generation, growth, and collapse of bubbles and will result in extreme local heating and high pressures in very short lifetimes. Typically, the cavitation resulted transient and localized hot spots have temperatures up to 5000 K, pressures of ∼ 1000 atm, and heating and cooling rates above 1010 K/s, serving a means of concentrating the diffuse energy of sound into a unique set of super conditions to produce unusual materials from precursors dissolved in solution through high-energy chemical reaction. As a result, a number of chemical reactions that were previously difficult to carry out by other heating methods can easily be accomplished using sonication [7].

Hot-injection method

Hot-injection synthesis provides a versatile method for the preparation of highly monodispersed colloidal nanocrystals with tunable size, shape, and surface passivation. The reason for the success of this approach lies in the use of nonionic precursors in high-boiling organic solvents. This makes it possible to grow the nanocrystals relatively slowly at a high temperature, which yields defect-free, well-passivated nanocrystals. The second important aspect of this type of synthesis is the separation of the nucleation and growth stages. Due to this, a high degree of monodispersity can be achieved without the use of postsynthesis size-selective techniques. Hot-injection synthesis has been proved to be a powerful method for the green syntheses of nanomaterials including quantum dots, upconversion nanoparticles, metal oxides, and perovskite nanocrystals [9].

Natural Nanomaterials and Their Characteristics

Natural nanomaterials (NNMs) are ubiquitous in the environment, resulting from many natural processes and anthropogenic impacts associated with volcanic eruptions, photochemical reactions, hydrothermal vent systems, weathering of rocks, precipitation reactions, and biological processes. Herein, we will highlight the characteristics of various NNMs in the whole biosphere including NNMs from various life entities, inorganic NNMs in aquatic and terrestrial systems, and NNMs in atmosphere.

NNMs From Life Entities

Life entities on earth have again and again shown us with their respective characters. For example, the self-cleaning property of lotus leaves, prey capture ability of pitcher plants, extraordinary climbing ability of geckos, architecturally elegant and adhesive spider webs, and colorful butterfly wings have astonished us all. In fact, the characteristics in these objects all involve in a myriad of well-designed NNMs.

Lotus leaves

Since ancient times, the lotus leaf has been known as a symbol of sacred purity for the characteristic of live in the silt but not imbrued. When water droplets fall upon the surface of a lotus leaf, they are almost spherical in shape and can easily roll off the leaf surface, collecting the dirt and other contamination particles (Fig. 1.1A and B) [10]. This phenomenon is the so-called lotus effect caused by the micro-/nanoscale roughness and the epicuticular wax on the surface of lotus leaves [11,12]. Papillae with several microns and cilium-like nanostructures covering on the papillae consist of the surface of lotus leaves (Fig. 1.1C and D) [13]. These surface structures endow the lotus leaf with superhydrophobic characteristics (the water contact angle (CA) of a lotus leaf is commonly higher than 160°, and the rolling angle is < 5°) [14].

Fig. 1.1 The superhydrophobicity and surface micro-/nanostructures of a lotus leaf. Self-cleaning of the adhering particles by water (A) and the spherical water droplet (B) on a lotus leaf. The microscale papillae and nanoscale cilium structures (C and D) under SEM [10]. Reused with permission from Koch K, Bhushan B, Barthlott W. Multifunctional surface structures of plants: an inspiration for biomimetics. Progr Mater Sci 2009;54:137–78. Copyright 2008, Elsevier.

Nepenthes pitcher plants

Nepenthes pitcher plants possess an instinct for capturing insects with the help of their slippery surface at the peristome and waxy zone in the pitcher-shaped leaves. The inner walls of the collar-shaped peristome are composed of downward-pointing projections and nectar pores [15]. Microsized radial ridges and nanogaps between two adjacent lunate epidermal cells can be observed at the peristome surface [12]. Contributed by such series of structures, the secreted nectar and the attracted moisture on the peristome surface can completely spread out and form a homogeneous water film, making it exceedingly slippery for insects [16,17]. This is the reason why insects are easier trapped in the pitcher under humid weather conditions. The waxy zone constituting 51.3% of the pitcher height is covered with two-layer platelike wax crystals [18]. The upper-layer wax crystals are densely arranged like roof tiles. The lower layer is composed of interconnected network of membranous platelets [19]. The chemical components of these waxes mainly include long-chain aldehydes, primary alcohols, and alkyl esters. These standing wax crystals, particularly the upper one, greatly reduce the contact area of the insect feet and the surface of the waxy zone, making it slippery for most insects even under dry conditions [17].

Gecko feet

The extraordinary climbing ability of geckos—they can readily stick to almost any surfaces—has aroused extensive interest. Secrets for the adhesive capability of gecko lie in the structures and functions of their feet and toe pads. Each toe of a tokay gecko possesses ~ 200,000 setae, and each seta terminates with hundreds of spatulas [20]. A single spatula consisting of a stalk with a thin, roughly triangular end is ~ 200 nm in length and also in width (Fig. 1.2) [21]. Research showed that the adhesion and friction forces are exactly generated at the spatula pads that appear to function as nanosized tapes or plates. Such structures form large real contact area whether at rough or smooth surfaces, bestowing the extraordinary attaching ability on gecko foot via the weak but universal van der Waals force together with capillary forces. Theoretically, the maximum friction force along the forward direction generated by a single seta can be 40–400 μN, hinging on the number of spatulas per setae [20]. A 50 g tokay gecko having 6.5 million setae can generate 1300 N of adhesion force, which is enough to support the weight of two humans. These data suggest that less than 0.04% of the setae in the 50 g gecko are needed to support its weight on a wall [22,23].

Fig. 1.2 Adhesive structures of the gecko feet. (A) SEMs of rows of setae from a toe, (B) a single seta, and (C) the spatulas of a seta [21]. Reused with permission from Autumn K, Liang YA, Hsieh ST, Zesch W, Chan WP, Kenny TW, et al. Adhesive force of a single gecko foot-hair. Nature 2000;405:681–5. Copyright 2000 Nature Publishing Group.

Spider web

Spider webs have existed for more than 100 million years. To date, there are five types of spider webs, that is, orb web, cobweb, funnel web, tubular web, and sheet web. Among these types of webs, orb web has been the most intensively studied one, which will be highlighted herein.

The architecturally elegant orb web is composed of dragline silks in radial array and spiral prey capture threads [24]. Cribellate threads are the most primitive prey capture threads, and each of the cribellate thread consists of a pair of central axial lines each with an average diameter of ~ 270 nm, dozens of smaller paracribellate fibrils around the axial fibers, and a cloud of thousands of looped fibrils in the outer sheath each with a diameter of ~ 18 nm [25]. In the evolution process, some cribellate threads were replaced by adhesive viscid capture threads in the modern orb weavers [24]. The viscid capture spirals are formed of a pair of supporting flagelliform axial silk fibers with diameters ranging from nanosize to micron-size covered by micron-sized glue droplets. And the viscid silk glue is heterogeneous with a dense polymeric core surrounded by a translucent mixture of glycoproteins and aqueous solution of low-molecular-weight hygroscopic salts. Viscid silk glue exhibits higher adhesive energy at faster stretching rates because of viscous dissipative forces. This characteristic benefits the capture of insects flying at high velocity [26,27]. As to the dragline silk, the remarkable mechanical properties including strength (1.1 GPa), stiffness (10 GPa), extensibility (27%), and toughness (180 MJ/m³) have been reported. Dragline silk can be three times tougher than Kevlar 49 and five times tougher than steel by weight [28].

Butterfly wings

The beautiful colors reflected from butterfly wings are attributed to pigments and periodic micro-/nanostructures, which are also referred to as chemical and physical colors, respectively [29]. Normally, both dorsal and ventral wing surfaces are covered with a layer of chitinous scales that are responsible for the reflected color (Fig. 1.3A and B) [31], and there are a series of longitudinal ridges and cross ribs on the scale surface with almost identical interspacing (Fig. 1.3C) [30]. These longitudinal ridges are composed of anteriorly overlapped scutes that are ~ 1.6 μm in length and ~ 100 nm in diameter. Two adjacent overlapped scutes are bound together by a row of subribs with a length of ~ 60 nm and a diameter of ∼ 20 nm (inset in Fig. 1.3C). These periodic components in the scale form the photonic structures and contribute to the colors [30]. Apart from the photonic characteristics, such micro- to nanostructures endow the butterfly wings with anisotropic superhydrophobic property (the water CA is 152 ± 2°). Water droplets can easily roll off the surface of a butterfly wing along the radial outward direction, keeping the wing clean from outside contaminants [12].

Fig. 1.3 Morphology and structure of the original butterfly wing surface ( Morpho peleides ) [30]. (A) A photo of the butterfly. (B) An optical microscope image of the scales from the blue area (dark gray in print versions). (C) A SEM image of the scale surface showing the longitudinal ridges and cross ribs. The inset is a higher-resolution SEM image showing the overlapped scutes and subribs in a longitudinal ridge. Adapted with permission from Huang J, Wang X, Wang ZL. Controlled replication of butterfly wings for achieving tunable photonic properties. Nano Lett 2006;6:2325–31. Copyright 2006 American Chemical Society.

Inorganic NNMs in Aquatic and Terrestrial Systems

Since there are many geologic processes in the Mother Nature associated with volcanic eruption, chemical deposition, and weathering, NNMs are widespread in aquatic and terrestrial systems. Considering that the NNMs described in Section 1.2.1 are organic-related, only inorganic NNMs will be presented in this section.

Clay

Clays are commonly present as a major component of soil, weathering rocks, volcanic deposits, continental and marine sediments, and fault gouge [32]. The term clay refers to a naturally occurring material composed primarily of fine-grained minerals, which is generally plastic at appropriate water contents and will harden when dried or fired [33]. The particle size of clay minerals can be ranged from tens of angstroms to millimeters. Many clay minerals form sheetlike particles or platelets, and the thickness of each layer is ~ 1 nm. Each layer is fundamentally built of one or two tetrahedral silicate (Si-O) sheets and one octahedral metal oxide/hydroxide (M-O or M-OH) sheet. As naturally nanoscale particles with a layered structure and interlayer space, clay possesses great potentiality in many advancing fields. The inherent features of clays, comprising large surface area, swellability, and naturally charged characteristics, make them to be good candidates for fillers and gellants. Besides, the chemically active properties of clay also make them suitable to be used as absorbents and catalysts [32,34].

Opal

Opals have been known and regarded as an unusual type of gemstone since ancient times. They impress people with their play-of-color property [35]. This mysterious property is the so-called opalescence derived from the periodic nanostructure. Unlike the butterfly wing structures, the periodic nanostructures in opals are 3-D photonic crystals. All opal layers exhibit nearly perfect face-centered cubic lattices with the feature that the (111) direction is aligned perpendicular to the film [36]. There are two types of opals: opal-CT and opal-A. Opal-CT refers to the disordered a-cristobalite with a-tridymite-type stacking as defined by Jones and Segnit [37,38], whereas opal-A refers to the amorphous type that is generally of sedimentary origin [39]. Opals consist of silica and varying amounts of water (mostly 4%–9%), but impurities such as Fe³ +, Al³ +, or Ti³ + can also be found.

Metallic nanomaterials

The nanosize of metallic nanomaterials endows them with a high surface-to-volume ratio and reactivity compared with a larger-size material with the same chemical composition, making them highly dynamic in environmental systems [40,41].

By combining the processes of reduction and oxidation under natural conditions, chemical transformations of metallic nanomaterials occur frequently. In some cases, a relatively inert oxide surface coating on the metallic nanoparticle can be formed via oxidation. In other cases, oxidation gradually corrodes the nanoparticle and then releases soluble ions [42]. Photocatalytic redox reactions (mainly by sunlight) have been proved to be very important processes to accelerate the transformation of naturally metallic nanomaterials (e.g., Ag NPs) by affecting the coatings, oxidation state, and generation of reactive oxygen species.

Sulfidation is another important process affecting the transformations of naturally metallic nanomaterial, which is particularly true for metallic nanomaterial made from class B metal cations (e.g., Ag, Zn, and Cu) [43]. Class B metal ions can strongly bind with electron-dense sulfur molecules, rendering these metal ions highly reactive with sulfur-containing compounds in sediments, soils, and air. The resultant metal-sulfide shell on the particle surface is relatively insoluble, altering the surface charge and finally inducing aggregation [44].

Biological transformations of metallic nanomaterials are also inevitable in environmental media and organisms. In all biological processes, redox reactions take place in the cell wall, cell membrane, cytoplasm, and extracellularly [43]. Currently, varieties of metallic nanomaterials, such as Ag, Au, CdS, and Fe3O4 NPs, have been found to be generated from biological processes [45–48].

NNMs in Atmosphere

Aerosols are the main nanomaterials in atmosphere. The major natural aerosols are sea salt, soil dust, natural sulfates, volcanic aerosols, and those generated by natural forest fires. Here, characteristics of the first top three natural aerosols, that is, sea salt, soil dust, and natural sulfates, will be described.

Sea salt aerosols

The most abundant natural aerosol is sea-salt aerosol, at an estimated 1000–10,000 Tg (about 30%–75% of the whole natural aerosols) per year. Sea-salt aerosols are hygroscopic and act as condensation nuclei for the cloud formation [49,50]. The airborne salt particles (mainly chloride) are originated from the sea spray at the wave crest by strong winds. At low wind speed, the sea-salt aerosol radiative forcing ranges from − 0.6 to − 2 W/m². However, the radiative forcing reaches as high as 1.5–4 W/m² at higher wind speeds [51]. Radiative property study showed that sea-salt aerosols are nonabsorbing in the visible region but completely absorbing in the long-wave region [52].

Dust aerosols

Dust aerosols originate from the soil, and weathered rocks are usually mineral aerosols [53]. Ultrafine dust aerosols are mostly formed by the winds in the arid regions. Dust particles with radii ranging from nanometer to submicron are feasible to transport long distances into the marine atmosphere [54]. Dust aerosols are significant contributors to radiative warming below 500 mb because of the short-wave absorption characteristic [55,56]. Unlike scattering aerosols (e.g., sea salt), dust radiative forcing rests upon the surface reflection [57]. The mineral dust transportation causes surface cooling accompanying with lower atmospheric heating. This can in turn intensify a low-level inversion, thus increasing atmospheric stability and reducing convection.

Sulfate aerosols

Biogenic emissions from the oceans, soils, and plants and emissions from volcanoes, biomass burning, and combustion of fossil fuel are the sources of atmospheric sulfate [58]. Most of the particles < 250 nm in clean marine air are composed of nonsea-salt sulfate. The conversion of gaseous dimethyl sulfide (DMS) and sulfur dioxide (SO2) to solid sulfate aerosol is more volatile than that of sea salt [59]. In the atmosphere, DMS can be oxidized by OH radicals, yielding SO2, methane sulfonic acid (MSA), H2SO4, and other compounds. By acid condensation, these nonsea-salt sulfate particles grow to a radius of 40 nm in about 2 days. This size is large enough to act as cloud condensation nuclei when the number of these sulfate particles reaches 30–200/cm³. Since the sulfate aerosol is of the nonabsorbing type (and hygroscopic), it partly offsets the warming caused by greenhouse gases and absorbing aerosols. An increasing number of sulfate aerosols result in enhanced cloud droplets, which in turn increases the albedo of clouds. Consequently, the short-wave solar radiation reaching the Earth's surface is decreased [60].

Characterization of Novel Nanomaterials

Novel nanomaterials are emerging extraordinary zero- and two-dimensional materials. The strong interests in nanomaterials derive from their unique physical and chemical properties and functionalities, such as morphology, structure, and properties, often differ significantly from their corresponding bulk counterparts. The most intuitive way to observe the morphologies of nanomaterials is by microscopes, including scanning electron microscope (SEM), transmission electron microscope (TEM), scanning tunneling microscope (STM), and atomic force microscope (AFM). Structure analysis is an important way to identify nanomaterials. As the commonly used structure analysis instruments, X-ray power diffraction (XRD), Raman spectrometer, X-ray absorption spectroscopy (XAS), and Fourier transform infrared (FTIR) spectroscopy are briefly introduced. Typical optical, electric, catalytic, and magnetic properties of novel nanomaterials are illustrated concisely. In this chapter, typical characterization of novel nanomaterials will be summarized.

Morphology Characterization of Nanomaterials

SEM

SEM is a convenient and widespread technique for illustrating the morphologies of materials with a spatial resolution below 1 nm [61,62]. The spatial resolution of the SEM depends not only on the aggregation of the emitted electrons but also on the interaction between the electrons with the surface of the samples. The secondary electrons are emitted as the interaction between the electrons with the surface of the samples occurs. The energy of the secondary electrons is typically below 50 eV. The emission efficiency significantly depends on geometry and elemental composition of the surface of the samples [63].

TEM

TEM is an efficient tool for high-spatial-resolution structural and chemical characterization [64]. A TEM can observe atoms at resolutions close to 0.1 nm in crystalline specimens, which is smaller than the interatomic distance. An electron beam focused close to 0.3 nm allows quantitative chemical analysis of a single nanocrystal. TEM analysis has significant impact for material characterization in the scale range from atoms to submicron. TEM can be used as an effective implement to gain information about size, morphology, crystallinity, and particle interaction of nanomaterials [61,65].

STM

Scanning probe microscopy (SPM) includes STM, AFM, and chemical force microscopy that have been extensively applied in nanostructure characterization [66,67]. STM is invented based on the mechanism of the quantum tunneling effect [68]. The wave function of the electrons in a solid extends into the vacuum and decays exponentially. If a tip is getting sufficiently close to the solid surface, the electron wave functions of the tip and that of the solid overlaps. Then, a given small electric voltage is applied; the tunneling of the electrons from the solid to the tip happens. Therefore, morphologies are obtained by detecting the tunneling current when the tip is scanned across the surface of the samples. The electronic structure of the solid surface can also be determined based on the detected C-V curves.

AFM

For nonconductive materials, AFM becomes an effective and fast method to characterize the surface fluctuation [66,69]. AFM operates in an analogous mechanism except the signal is the force between the tip and the solid surface. The interaction between two atoms is repulsive at short range and attractive at long range. The force applied on the tip illustrates the distance between the tip and the solid surface. Therefore, the morphology images of the solid surface can be achieved by measuring the force applied on the tip.

Structure Characterization of Nanomaterials

XRD

X-ray diffraction (XRD) is an on-destructive and powerful method for determining phase structure and phase composition of materials. Diffraction patterns in wide-angle region are directly related to the atomic structure of the nanocrystals, whereas the pattern in the small-angle region manifests information about the ordered assembly of nanocrystals [70–72]. Small-angle scattering is used to evaluate the average interparticle distance, while wide-angle diffraction is used to refine the atomic structure of nanoclusters [65]. The widths of the diffraction peaks of nanocrystals significantly depended on the average grain sizes, defect amounts, and internal stress. Therefore, the full width at half maximum (FWHM) of the characteristic XRD peaks can be used to estimate the average grain sizes of the materials [73]. However, this method will be appropriate for calculating the grain sizes when the values vary in the range of 1–100 nm.

Raman spectroscopy

Optical spectroscopy is commonly used in nanomaterials' structure characterization. IR and Raman provide direct structure features, while UV-visible absorption and photoluminescence (PL) provide indirect structural features. High crystallinity and large nanoparticle size give rise to sharp Raman peaks and strong Raman signal. High density of defects and disorder results in defect-state luminescence and low PL yield [74,75]. Dynamic light scattering (DLS) is a supplementary means to measure the hydrated ionic size of nanoparticles in solution. In general, optical spectroscopy is sensitive to structural properties and can provide an indirect prove to the structural information.

Raman and IR spectrum provide information about the structure such as vibrational frequencies and surface functional group integrity of nanoparticles. Raman scattering is a nonlinear optical phenomenon that involves two photons and inelastic scattering. In recent years, Raman spectrum has become a powerful technique to study specific molecules. For nanomaterials, Raman spectrum can be used to study electron-phonon coupling, vibrational or phonon modes, and symmetries of excited electronic states.

FT-IR

Since the 1950s, IR spectroscopy has become a popular analytic technique for lignin chemists. In the last decade, FTIR spectrometers have been increasingly significant in research work [76,77]. FTIR is one of the most widely used tools in the oil analysis. It is a purely instrument-based test free from multifarious sample preparation. It has the fascinating metrics including time-saving, convenient, economical, practical, multifunctional, and universal. It can detect water-soluble compounds, organic compounds, and certain additives. FTIR is based on the fundamental principles of molecular spectroscopy. The basic mechanism of molecular spectroscopy is that molecules absorb light energy at specific wavelengths (their resonance frequencies) [78,79]. For example, the water molecule has a specific resonates around the wave number of 3450 cm− 1 in the infrared region.

In an FTIR spectrometer, the samples were motivated by an infrared light source around the wave number from 4000 to 400 cm− 1. The intensity of light transmittance of the sample is measured with one wave-number interval. The difference of light intensity between the excitation and transmitting beams was determined by the detector. FTIR spectroscopy is a rapid, convenient, and intact technique. It allows the qualitative detection of organic compounds or surrounding functional groups since the characteristic vibrational mode of each molecular group causes the appearance of bands in the infrared spectrum at a specific frequency. Moreover, FTIR technique is an effective way for quantitative analysis as the relative intensities of the characteristic bands in the spectrum are proportional to their concentration [80].

XAS

X-ray-based spectroscopies are indispensable in determining the chemical composition of nanomaterials. These techniques contain XAS such as extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), X-ray fluorescence (XRF) spectroscopy, energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) [81,82]. Most of them are detected and analyzed by the samples' absorbed radiation or their emission radiation after excitation with X-rays, with the exception that electrons are analyzed in XPS. The specific spectroscopic features of specific elements make them useful for sample elemental analysis. Each element in the periodic table has a unique electronic structure, thus a unique response to electromagnetic radiation.

XAS is an element-specific probe of the local structure of atoms or ions in a sample. XAS spectrum analysis can use standard known structures or use theory to deduce material structure. In either case, the qualitative analysis of the material is determined by its unique local structure. XAS results from the absorption of a high-energy X-ray by an atom in a sample. This absorption spectrum corresponds to the binding energy of the electron in the material. Occasionally, vacant bound electronic states appear near the valence or conduction bands. As a result, distinct absorptions will result at these energies in the diagnostic of coordination. XAS is mainly composed of two spectral regions. The first is the X-ray absorption near-edge structure or the XANES spectral region [81]. The XANES technique is sensitive to the valence state and speciation of the element of interest and thus is often used to determine oxidation state and coordination environment of materials. Standard spectra are often used to determine which species are present in an unknown sample. XANES is sensitive to bonding environment and oxidation state; thus, it is capable to discriminate species of similar formal oxidation state but different coordination. The high-energy region of the X-ray absorption spectrum is EXAFS region (termed as the extended X-ray absorption fine structure). EXAFS contains a great deal of information, including the identity of adjacent atoms, their distance from the excited atom, the number of neighboring atoms in the nearest shell, and the degree of disorder in a particular atomic shell.

XRF is a technique in determining elemental composition of a material. The technique is based on irradiating a sample with either monochromatic radiation obtained from a synchrotron or an X-ray source. The emitted X-rays are the characteristic spectrum of the element contained in the substance.

XPS is used to measure the specific photoelectrons of a sample following X-ray excitation. It is a quantitative spectroscopic technique that can detect the chemical composition and electronic state of all elements in a material. XPS spectra are obtained by irradiating a material with a beam of X-rays. At the same time, the kinetic energy and number of electrons that escape from the top 1–10 nm of the material are analyzed. Therefore, XPS is a sensitive surface analytic technique, and it requires ultrahigh-vacuum (UHV) conditions [82].

Properties Characterization of Nanomaterials

Optical properties

Optical properties are commonly characterized using spectroscopic techniques including UV-visible and photoluminescence spectroscopy. The UV-visible absorption measured as a function of wavelength reflects the strength of the electronic transition between the valence band (VB) and the conduction band (CB). The electronic transition from the VB to the CB is the solid-state analog to the HOMO-LUMO electronic transition in molecules. The difference of energies between the bottom component of the CB and excited state is defined as the binding energy of electron-hole pairs. Thus, determination on the position of the excited absorption peak offers an estimation on the bandgap of the nanomaterials. The bandgap energy increases as the grain size decreases, producing both blueshift of the absorption spectrum and the excited peak.

In photoluminescence spectroscopy, the emission signals of photos are measured following the excitation of the sample with a fixed wavelength of light. Photoluminescence reveals that the electrons transit from the excited state to the valence band. Photoluminescence shows a significantly higher sensitivity than the UV-visible absorption technique [83]. The photoluminescence provides a sensitive probe of bandgap states that UV-visible spectroscopy is much less sensitive to. For a typical nanoparticle sample, PL can be generally divided into band-edge emission, including excitonic emission, and trap-state emission. In addition, trap-state PL is often characterized by a large bandwidth reflecting a broad energy distribution of emitting states. A strong trap-state emission usually illustrates a high density of trap states and efficient electron-hole trapping.

In addition to the optical absorption and the emission features, other properties of nanomaterials such as chemiluminescence (CL) and electroluminescence (EL) are of interest for technological applications such as chemical sensing and biochemical detection.

Electrochemical properties

Electrochemistry aims to investigate the relationship between the chemistry reactions and electricity, including the investigation on chemical changes caused by the passage of an electric current across a medium, as well as the production of electric energy by chemical reactions [84–86]. Electrochemistry also embraces the study of electrolyte solutions and the chemical equilibriums that occur in them. Electrochemical science shows applications in both solar technology and biomedical innovations.

The batteries that are used in cellphones, cameras, etc. are electrochemical cells [87]. The electrochemical cells that supply the electric energy from chemical energy are the basis of primary and secondary storage batteries and fuel cells. Other electric phenomena of interest in chemical systems include the behavior of ionic solutions and the conduction of current through these solutions, the separation of ions by an electric field, the corrosion and passivation of metals, the electric effects in biological systems (bioelectrochemistry), and the effect of light on electrochemical cells (photoelectrochemistry) [88].

Catalytic properties

An extensive application of nanomaterials has been in the field of catalysis. Plenty of surface atoms increase the surface activities of nanocrystals significantly. The unique surface structure, electronic states, and largely exposed surface area are required for stimulating and promoting chemical reactions. The size-dependent catalytic properties of nanocrystals have been widely studied, while only scant information about the shape-dependent catalytic behavior has been recorded. The recent success in synthesizing shape-controlled nanocrystals is a step forward in this field.

Magnetic properties

The applications of magnetic nanocrystals such as information storage and bioprocessing [89] draw extensive attentions in the last decades. Magnetic properties of nanomaterials differ significantly from the bulk materials attributed to two primary factors. The large specific surface area of nanomaterials produces a fancy local environment for atoms on surface in their magnetic coupling/interaction with neighboring atoms, resulting in the mixed volume and surface magnetic characteristics. The nanosize ferromagnetic particles consist only a single magnetic domain, which is different from the bulk materials. In the case of a single particle being a single domain, the super paramagnetism occurs, in which the magnetizations of the particles are randomly distributed and they are aligned only under an applied magnetic field, and the alignment disappears once the external field is withdrawn. In the application of ultracompact information storage [90,91], the limit of the storage capacity is determined by the average sizes of the domains.

Biomedical Diagnosis, Bioimaging and Therapy

Over the last few years, composite nanomaterials have had a great impact on biosensing. Significant progresses have been made in synthetic methodologies. It is possible to prepare various nanomaterials with highly controllable size, shape, surface charge, and physicochemical characteristics. Consequently, the professional and public exposure to nanomaterials is supposed to increase dramatically in the coming years. Nanomaterials possess unique optical, electronic, catalytic, and magnetic properties that may endow significant advances in biomedical applications. This volume will highlight the latest biomedical diagnosis, bioimaging, and therapy of a wide range of nanomaterials including carbon-based nanomaterials (CBNs), two-dimensional TMD nanosheets, noble metal nanoparticles, upconversion nanoparticles, and composite nanomaterials.

Carbon-Based Nanomaterials

Recently, CBNs are considered to be one of the key components in nanotechnology. CBNs contain a variety of forms, such as fullerenes, carbon nanotubes, carbon nanoparticles, carbon dots, graphene quantum dots (GQDs), and graphitic carbon nitride (g-C3N4) nanomaterial. Their applications range from mechanical engineering to biomedicine [92–95]. The most typical CBNs were carbon dots.

Carbon dots are small carbon nanoparticles less than 10 nm in size. They have multiple advantages over traditional semiconductor quantum, including comparable optical properties, environmental friendliness, chemical inertness, superiority in water solubility, ease of modification, and good photochemical stability. In principle, the carbon inner cores are nontoxic, and any cytotoxicity of CQDs is primarily due to the superficial passivating agents [96]. CQDs modified with cytotoxicity surface-passivating agents can be used for in vivo imaging if these agents are maintained at low concentrations and/or with short incubation time. In MCF-7 cells, water-soluble CQDs passivated with PPEI-EI existed mostly in the cell membrane and cytoplasm; none of them reach the nucleus [97]. The same situation happened in CQDs synthesized from activated carbon in COS-7 cells [98]. In other cases, silica-encapsulated CQDs were found labeled in the cytoplasm [99]. CQDs enclosed in an amphiphilic polymer were also found in the cytosol in Chinese hamster ovary cell [100]. These examples clearly show that the CQDs are excellent bioimaging materials and the residence location of CQD varies, depending on the character of the surface-passivating agents and the surface passivation method.

CQDs are very attractive in nanomedicine owing to their simple synthetic methods and their nontoxicity in vivo studies [101]. After intravenously injected with CQDs, the organs and viscera functions of the mice remain normal after tested for 4 weeks. The high biocompatibility of CQDs was also verified by prothrombin time assays in plasma samples [102]. CQDs can also be used for photodynamic therapy (PDT). PDT is a clinical treatment that involves the localization and accumulation of photosensitizers for superficial tumor tissue treatment [103]. Singlet oxygen species were generated after irradiated by a specific wavelength and result in cell death. The CQDs have tunable wavelength and can be used as longer-wavelength photosensitizers, which allow deeper tissue PDT.

Two-Dimensional Transition Metal Dichalcogenide Nanosheets

Ultrathin two-dimensional layered TMD nanosheets, such as MoS2, WS2, MoSe2, and WSe2, are emerging as a new nanomaterial due to their unique chemical and electronic properties [104–106]. Though the TMD nanosheets possess a 2-D planar structure as graphene, the physical, chemical, and electronic properties of TMD nanosheets are different from those of graphene sheets.

The unique optical properties and high specific surface area make TMD nanosheets very popular in biomedical applications [107–110]. In general, post functionalization with hydrophilic polymers is necessary to enhance TMD nanosheets' stability and biocompatibility. For example, Liu et al. [107] found the 2-D PEG-WS2 with favorable stability, biocompatibility, and strong NIR absorbance. These merits make them potential application in dual-modal computed tomography (CT)/photoacoustic imaging-guided PDT in vivo. Later, PEG-MoS2 hybrid nanosheets were found to be an efficient carrier in drug delivery for combined PDT and chemotherapy of cancer owing to their high surface-area-to-mass ratio of ultrathin MoS2 sheets [108]. Then, it was also reported that the chitosan-modified MoS2 nanosheets can be used as promising contrast agents for CT imaging [109]. These fascinating studies offer a new way for the application of TMD-nanosheet-based composite nanomaterials in biomedical applications [111].

Noble Metal Nanoparticles

Noble metal nanoparticles such as gold, silver, and their compound exhibit a variety of biomedical applications in the fields of medical diagnosis, drug/gene delivery, thermal ablation, and PDT enhancement [112–120]. Numerous methods have been developed to synthesize noble metal NPs, including physical methods (e.g., grinding, vapor deposition, and laser ablation) and chemical methods (e.g., photochemical reduction, thermal decomposition, chemical reduction, coprecipitation, and hydrolysis). Noble metal nanoparticles with homogeneity in size, shape, and surface properties have potential applications for bioimaging, biomedical diagnosis, and therapy [121–125]. As one member of nanomaterials for biomedical applications, noble-metal-based nanoparticles have already open up the possibility of creating new diagnostic platforms for disease and threat detection in the early stage. Among various traditional approaches, such as colorimetric, fluorescence, NIR imaging, SERS, and electrochemical sensing, advantages and disadvantages are always associated with each method toward the practical biomedical application in real samples. This chapter will review the fabrication and performance of the noble metal NPs and illustrate their benefits in biomedical applications, including diagnosis, bioimaging, and therapy.

Effects of Nanomaterials on Environment and Organism

The proliferation of nanomaterials (NMs) has brought diverse benefits to the human beings in the form of cosmetics, food packaging, drug delivery systems, therapeutics, biosensors, and others [126]. Thus, their exposures to human beings and release into the environment are more and more frequent, which arouses the attention devoted to their toxicity to human health and environment. It is necessary to uncover and understand how NMs enter and influence human beings and environment. The debates on the inherent decisive factors for the toxicity of NMs and the appraisal assessment models of the toxicity for NMs should be carried out.

Inherent Decisive Factors on the Toxicity of NMs

The physiochemical properties of NMs play an important role in the toxicity of NMs, including size, shape, composition, surface charge, and surface functionalization.

Firstly, the size of NMs is considered as the most important factor for their toxicity [127]. Generally, smaller NMs taken up via cells through pinocytosis more easily generate inflammation than large ones taken by phagocytosis [128–132]. Moreover, in comparison with large NMs, the small ones are more biocompatible with higher cellular uptake efficiency [133], and more opportunities appear in cellular organelles (liver, spleen, bone marrow, etc.) [134,135]. Then, NMs with different shapes (e.g., spheres, tubes, rings, stars, and planes) can influence the membrane warping process during endocytosis or phagocytosis. It is believed that the shape-dependent toxicity of NMs is imparted through their adverse effects on endocytosis or clearance by macrophages [136,137]. In fact, the shape of NMs directly affects their endocytosis pathways, efficiency of cellular uptake, and aggregation [138]. Furthermore, the tunable compositions of NMs lead to the various behaviors under biological conditions including cellular uptake, biotransformation, and fate of NMs, which ultimately determines their toxicity to be acute and chronic. In comparison, the carbon-based NMs are generally considered as more biocompatible and environmentally friendly than metal-based NMs, especially for semiconductor quantum dots due to the toxicity caused by their inherent heavy metal ions [139]. Additionally, proper surface functionalization of NMs can improve their physicochemical properties and mitigate or eliminate their adverse effects. However, the implications for their potential to induce biological effects from surface functionalization should be taken into consideration. Finally, surface charge is another significant factor that affects the efficiency and pathway of cellular uptake of NMs [140]. In general, positively charged NMs possess higher cellular uptake efficiency than those with neutral or negative surface charge due to the stronger affinity of positively charged NMs to the negatively charged cell membrane [141]. And the surface charge is also related to the manner of cell death [142].

Routes for NMs Entering Into Environment and Organism

There are four main routes for NMs entering the environment and organism: skin penetration, inhalation, gastrointestinal tract, and intravenous injections. The skin is the largest organ of the body and serves as one of the major routes of exposure to environmental toxicant including NMs to gain access to a biological system. Though NMs are difficult to enter into the intact skin tissue due to the protection from the epidermis, the NMs may cause defects in the skin barrier due to skin flexion, wounds, scrapes, abrasion, or pinching [143–145]. Aerosolized NMs can easily enter the human body via inhalation and deposit within the alveolar regions of the lung due to their highly mobility. The inhaled NMs can effectively deposit in human lungs and mostly in the alveoli [146]. Gastrointestinal tract may also occur by unintentional hand-to-mouth transfer [146]. In addition, the inhaled NMs may be translocated via the mucociliary escalator and subsequently be ingested into the gastrointestinal tract. Theoretically, NMs once in the submucosal region are capable to enter both lymphatics and capillaries, where lymphatic absorption may give rise to immune response and capillaries bring NMs to the liver, the first checkpoint for everything absorbed through gastrointestinal tract before becoming systemic [147]. Intravenous administration of NMs aims to deliver the NMs to reserved sites rather than for systematic distribution for special medical purposes such as early detection, biomedical imaging, and therapy of diseases. The intravascularly injected NMs would be absorbed prior to they are distributed into other organs via blood