Showing papers in "Small in 2009"

Core/Shell semiconductor nanocrystals.

Abstract: Colloidal core/shell nanocrystals contain at least two semiconductor materials in an onionlike structure. The possibility to tune the basic optical properties of the core nanocrystals, for example, their fluorescence wavelength, quantum yield, and lifetime, by growing an epitaxial-type shell of another semiconductor has fueled significant progress on the chemical synthesis of these systems. In such core/shell nanocrystals, the shell provides a physical barrier between the optically active core and the surrounding medium, thus making the nanocrystals less sensitive to environmental changes, surface chemistry, and photo-oxidation. The shell further provides an efficient passivation of the surface trap states, giving rise to a strongly enhanced fluorescence quantum yield. This effect is a fundamental prerequisite for the use of nanocrystals in applications such as biological labeling and light-emitting devices, which rely on their emission properties. Focusing on recent advances, this Review discusses the fundamental properties and synthesis methods of core/shell and core/multiple shell structures of II-VI, IV-VI, and III-V semiconductors.

Nanoscale Forces and Their Uses in Self‐Assembly

Abstract: The ability to assemble nanoscopic components into larger structures and materials depends crucially on the ability to understand in quantitative detail and subsequently "engineer" the interparticle interactions. This Review provides a critical examination of the various interparticle forces (van der Waals, electrostatic, magnetic, molecular, and entropic) that can be used in nanoscale self-assembly. For each type of interaction, the magnitude and the length scale are discussed, as well as the scaling with particle size and interparticle distance. In all cases, the discussion emphasizes characteristics unique to the nanoscale. These theoretical considerations are accompanied by examples of recent experimental systems, in which specific interaction types were used to drive nanoscopic self-assembly. Overall, this Review aims to provide a comprehensive yet easily accessible resource of nanoscale-specific interparticle forces that can be implemented in models or simulations of self-assembly processes at this scale.

Cellular uptake and cytotoxicity of gold nanorods: molecular origin of cytotoxicity and surface effects.

Abstract: Gold nanorods of different aspect ratios are prepared using the growth-directing surfactant, cetyltrimethylammonium bromide (CTAB), which forms a bilayer on the gold nanorod surface. Toxicological assays of CTAB-capped nanorod solutions with human colon carcinoma cells (HT-29) reveal that the apparent cytotoxicity is caused by free CTAB in solution. Overcoating the nanorods with polymers substantially reduces cytotoxicity. The number of nanorods taken up per cell, for the different surface coatings, is quantitated by inductively coupled plasma mass spectrometry on washed cells; the number of nanorods per cell varies from 50 to 2300, depending on the surface chemistry. Serum proteins from the biological media, most likely bovine serum albumin, adsorb to gold nanorods, leading to all nanorod samples bearing the same effective charge, regardless of the initial nanorod surface charge. The results suggest that physiochemical surface properties of nanomaterials change substantially after coming into contact with biological media. Such changes should be taken into consideration when examining the biological properties or environmental impact of nanoparticles.

Size effect on cell uptake in well-suspended, uniform mesoporous silica nanoparticles.

Abstract: because itdetermines the mechanism and rate of cell uptake of ananoparticle and its ability to permeate through tissue. Theinvestigation of particle size effects will impact on allapplications of nanoparticles in biomedicine. It has beenfoundthatparticlesizecanaffecttheefficiencyandpathwayofcellularuptakebyinfluencingtheadhesionoftheparticlesandtheir interaction with cells.

Colloidal Gold and Silver Triangular Nanoprisms

Abstract: It is now well-known that the size, shape, and composition of nanomaterials can dramatically affect their physical and chemical properties, and that technologies based on nanoscale materials have the potential to revolutionize fields ranging from catalysis to medicine. Among these materials, anisotropic particles are particularly interesting because the decreased symmetry of such particles often leads to new and unusual chemical and physical behavior. Within this class of particles, triangular Au and Ag nanoprisms stand out due to their structure- and environment-dependent optical features, their anisotropic surface energetics, and the emergence of reliable synthetic methods for producing them in bulk quantities with control over their edge lengths and thickness. This Review will describe a variety of solution-based methods for synthesizing Au and Ag triangular prismatic structures, and will address and discuss proposed mechanisms for their formation.

One-Dimensional Composite Nanomaterials: Synthesis by Electrospinning and Their Applications

Abstract: This Review provides an overview of the synthesis of one-dimensional (1D) composite nanomaterials by electrospinning and their applications. After a brief description of the development of the electrospinning technique, the transformation of an inorganic nanocomponent or polymer into another kind of polymer or inorganic matrix is discussed in terms of the electrospinning process, including the direct-dispersed method, gas-solid reaction, in situ photoreduction, sol-gel method, emulsion electrospinning method, solvent evaporation, and coaxial electrospinning. In addition, various applications of such 1D composite nanomaterials are highlighted in terms of electronic and optical nanodevices, chemical and biological sensors, catalysis and electrocatalysis, superhydrophobic surfaces, environment, energy, and biomedical fields. An increasing number of investigations show that electrospinning has been not only a focus of academic study in the laboratory but is also being applied in a great many technological fields.

Gold nanoparticles of diameter 1.4 nm trigger necrosis by oxidative stress and mitochondrial damage.

Abstract: Gold nanoparticles (AuNPs) are generally considered nontoxic, similar to bulk gold, which is inert and biocompatible. AuNPs of diameter 1.4 nm capped with triphenylphosphine monosulfonate (TPPMS), Au1.4MS, are much more cytotoxic than 15-nm nanoparticles (Au15MS) of similar chemical composition. Here, major cell-death pathways are studied and it is determined that the cytotoxicity is caused by oxidative stress. Indicators of oxidative stress, reactive oxygen species (ROS), mitochondrial potential and integrity, and mitochondrial substrate reduction are all compromised. Genome-wide expression profiling using DNA gene arrays indicates robust upregulation of stress-related genes after 6 and 12 h of incubation with a 2 x IC50 concentration of Au1.4MS but not with Au15MS nanoparticles. The caspase inhibitor Z-VAD-fmk does not rescue the cells, which suggests that necrosis, not apoptosis, is the predominant pathway at this concentration. Pretreatment of the nanoparticles with reducing agents/antioxidants N-acetylcysteine, glutathione, and TPPMS reduces the toxicity of Au1.4MS. AuNPs of similar size but capped with glutathione (Au1.1GSH) likewise do not induce oxidative stress. Besides the size dependency of AuNP toxicity, ligand chemistry is a critical parameter determining the degree of cytotoxicity. AuNP exposure most likely causes oxidative stress that is amplified by mitochondrial damage. Au1.4MS nanoparticle cytotoxicity is associated with oxidative stress, endogenous ROS production, and depletion of the intracellular antioxidant pool.

Anti‐inflammatory Properties of Cerium Oxide Nanoparticles

Abstract: The valence and oxygen defect properties of cerium oxide nanoparticles (nanoceria) suggest that they may act as auto-regenerative free radical scavengers. Overproduction of the free radical nitric oxide (NO) by the enzyme inducible nitric oxide synthase (iNOS) has been implicated as a critical mediator of inflammation. NO is correlated with disease activity and contributes to tissue destruction. The ability of nanoceria to scavenge free radicals, or reactive oxygen species (ROS), and inhibit inflammatory mediator production in J774A.1 murine macrophages is investigated. Cells internalize nanoceria, the treatment is nontoxic, and oxidative stress and pro-inflammatory iNOS protein expression are abated with stimulation. In vivo studies show nanoceria deposition in mouse tissues with no pathogenicity. Taken together, it is suggested that cerium oxide nanoparticles are well tolerated in mice and are incorporated into cellular tissues. Furthermore, nanoceria may have the potential to reduce ROS production in states of inflammation and therefore serve as a novel therapy for chronic inflammation.

Co‐delivery of Doxorubicin and Bcl‐2 siRNA by Mesoporous Silica Nanoparticles Enhances the Efficacy of Chemotherapy in Multidrug‐Resistant Cancer Cells

Abstract: Development of multidrug resistance in cancer cells and adverse side effects are the major obstacles for effective cancer chemotherapy.[1-3] Therapeutic strategies to overcome drug resistance and specific tumor targeting with minimal premature drug release should have a great impact on the treatment of cancer. The term multidrug resistance (MDR) is used to define a resistance phenotype where cancer cells become resistant simultaneously to multiple drugs with no obvious structural resemblance and with different molecular targets.[4, 5] The multidrug resistance can be divided into two distinct classes, pump and nonpump resistance.[3] The pump resistance is caused by certain proteins that form membrane-bound ATP-dependent active drug efflux pumps, which significantly decrease the intracellular concentration of the drug and thereby the efficacy of the treatment. Membrane proteins, P-glycoprotein (Pgp) and multidrug resistance-associated protein (MRP) have been shown to be the main players for pump resistance to a broad range of structurally and functionally distinct cytotoxic agents.[6] The main mechanism of nonpump resistance is an activation of cellular antiapoptotic defense, mainly by Bcl-2 protein. Most of the anticancer drugs trigger apoptosis and simultaneously activate both pump and nonpump cellular defense of multidrug resistance, which prevents cell death. Therefore, to effectively suppress the overall resistance to chemotherapy, it is essential to simultaneously inhibit both pump and nonpump mechanisms of cellular resistance by targeting all the intracellular molecular targets.[3, 7-9]

Toxicity Assessments of Multisized Gold and Silver Nanoparticles in Zebrafish Embryos

Abstract: The potential toxicity of nanoparticles is addressed by utilizing a putative attractive model in developmental biology and genetics: the zebrafish (Danio rerio). Transparent zebrafish embryos, possessing a high degree of homology to the human genome, offer an economically feasible, medium-throughput screening platform for noninvasive real-time assessments of toxicity. Using colloidal silver (cAg) and gold nanoparticles (cAu) in a panoply of sizes (3, 10, 50, and 100 nm) and a semiquantitative scoring system, it is found that cAg produces almost 100% mortality at 120 h post-fertilization, while cAu produces less than 3% mortality at the same time point. Furthermore, while cAu induces minimal sublethal toxic effects, cAg treatments generate a variety of embryonic morphological malformations. Both cAg and cAu are taken up by the embryos and control experiments, suggesting that cAg toxicity is caused by the nanoparticles themselves or Ag(+) that is formed during in vivo nanoparticle destabilization. Although cAg toxicity is slightly size dependent at certain concentrations and time points, the most striking result is that parallel sizes of cAg and cAu induce significantly different toxic profiles, with the former being toxic and the latter being inert in all exposed sizes. Therefore, it is proposed that nanoparticle chemistry is as, if not more, important than specific nanosizes at inducing toxicity in vivo. Ultimately such assessments using the zebrafish embryo model should lead to the identification of nanomaterial characteristics that afford minimal or no toxicity and guide more rational designs of materials on the nanoscale.

Mesoporous-silica-coated up-conversion fluorescent nanoparticles for photodynamic therapy.

Abstract: Near-infrared (NIR)-to-visible up-conversion fluorescent nanoparticles have potential to be used for photodynamic therapy (PDT) in deep tissue because NIR light can penetrate thick tissue due to weak absorption in the optical window. Here a uniform layer of mesoporous silica is coated onto NaYF(4) up-converting nanocrystals, with a large surface area of approximately 770 m(2) g(-1) and an average pore size of 2 nm. A photosensitizer, zinc phthalocyanine, is incorporated into the mesoporous silica. Upon excitation by a NIR laser, the nanocrystals convert NIR light to visible light, which further activates the photosensitizer to release reactive singlet oxygen to kill cancer cells. The photosensitizer encapsulated in mesoporous silica is protected from degradation in the harsh biological environment. It is demonstrated that the photosensitizers loaded into the porous silica shell of the nanoparticles are not released out of the silica while they continuously produce singlet oxygen upon excitation by a NIR laser. The nanoparticles are reusable as the photosensitizers encapsulated in the silica are removed by soaking in ethanol.

Cytotoxicity and immunological response of gold and silver nanoparticles of different sizes.

Abstract: The immunological response of macrophages to physically produced pure Au and Ag nanoparticles (NPs) (in three different sizes) is investigated in vitro. The treatment of either type of NP at ≥10 ppm dramatically decreases the population and increases the size of the macrophages. Both NPs enter the cells but only AuNPs (especially those with smaller diamter) up-regulate the expressions of proinflammatory genes interlukin-1 (IL-1), interlukin-6 (IL-6), and tumor necrosis factor (TNF-α). Transmission electron microscopy images show that AuNPs and AgNPs are both trapped in vesicles in the cytoplasma, but only AuNPs are organized into a circular pattern. It is speculated that part of the negatively charged AuNPs might adsorb serum protein and enter cells via the more complicated endocytotic pathway, which results in higher cytotoxicity and immunological response of AuNPs as compared to AgNPS.

Catalytic Microtubular Jet Engines Self‐Propelled by Accumulated Gas Bubbles

Abstract: Strain-engineered microtubes with an inner catalytic surface serve as self-propelled microjet engines with speeds of up to approximately 2 mm s(-1) (approximately 50 body lengths per second). The motion of the microjets is caused by gas bubbles ejecting from one opening of the tube, and the velocity can be well approximated by the product of the bubble radius and the bubble ejection frequency. Trajectories of various different geometries are well visualized by long microbubble tails. If a magnetic layer is integrated into the wall of the microjet engine, we can control and localize the trajectories by applying external rotating magnetic fields. Fluid (i.e., fuel) pumping through the microtubes is revealed and directly clarifies the working principle of the catalytic microjet engines.

Doping single-layer graphene with aromatic molecules.

Abstract: Recently discovered single-layer graphene (SLG) has attracted great attention not only because this perfect 2-dimensional carbon crystalline structure enables unprecedented explorations of fundamental physics but also because of its exciting potentials in the post-silicon nanoeletronics 1-6 . As the electrical properties of SLG films are very sensitive to the local perturbations such as from surface charges 7-9 and adsorbed gas molecules 6 , it is plausible that the electronic structures, hence the performance, of SLG may be tailored by molecular doping on its surface. Herein, we demonstrated that the electronic structures of SLG can be differentially modulated by doping from various aromatic molecules. We also show that a simple spectroscopic method based on the Raman 2D and G band frequency sampling can be used to distinguish the n- and p-doped SLG. Raman spectroscopy is a powerful tool to rapidly and nondestructively examine intrinsic physical properties of various carbon nanostructures, including flat and one-atom thick carbon crystalline layer (graphene monolayer), stacked graphenes (graphite), and roll-up graphene monolayer (single-walled carbon nanotube–SWNT). The characteristic G (~1580-1590 cm -1 ) and 2D (~2690-2710 cm -1 ) Raman bands are able to reveal the number of stacked graphene layer 10-12 and the changes in charge carrier concentration (or Fermi energy shift) induced by static electrical field 13-14 .

Uptake, Translocation, and Transmission of Carbon Nanomaterials in Rice Plants

Abstract: Recent development of nanotechnology has reshaped the landscape of modern science and technology, while in the meantime raised concerns about the adverse effects of nanomaterials on biological systems and the environment. Owing to their mutual interaction, carbon-based nanomaterials readily aggregate and are not considered potential contaminants in the liquid phase. However, when discharged into the environment, the hydrophobicity of nanomaterials can be averted through their interaction with natural organic matter (NOM), a heterogeneous mixture of decomposed animals and plants and a major pollutant carrier in nature. Consequently, mobile NOM-modified nanomaterials may pose a threat to ecological terrestrial species through further physical, chemical, and biological processes. The impact of nanomaterials on high plants has scantly been examined in the current literature. Among the studies available, none have used major food crops or carbon nanoparticles (a major class of nanomaterials) for their evaluations. Although both enhanced and inhibited growth have been reported for vegetations exposed to nanomaterials at various developmental stages, including seed germina-

Size‐Dependent Cytotoxicity of Monodisperse Silica Nanoparticles in Human Endothelial Cells

Abstract: The effect that monodisperse amorphous spherical silica particles of different sizes have on the viability of endothelial cells (EAHY926 cell line) is investigated. The results indicate that exposure to silica nanoparticles causes cytotoxic damage (as indicated by lactate dehydrogenase (LDH) release) and a decrease in cell survival (as determined by the tetrazolium reduction, MTT, assay) in the EAHY926 cell line in a dose-related manner. Concentrations leading to a 50% reduction in cell viability (TC(50)) for the smallest particles tested (14-, 15-, and 16-nm diameter) ranging from 33 to 47 microg cm(-2) of cell culture differ significantly from values assessed for the bigger nanoparticles: 89 and 254 microg cm(-2) (diameter of 19 and 60 nm, respectively). Two fine silica particles with diameters of 104 and 335 nm show very low cytotoxic response compared to nanometer-sized particles with TC(50) values of 1095 and 1087 microg cm(-2), respectively. The smaller particles also appear to affect the exposed cells faster with cell death (by necrosis) being observed within just a few hours. The surface area of the tested particles is an important parameter in determining the toxicity of monodisperse amorphous silica nanoparticles.

Preparation of monodisperse biodegradable polymer microparticles using a microfluidic flow-focusing device for controlled drug delivery.

Abstract: Degradable microparticles have broad utility as vehicles for drug delivery and form the basis of several therapies approved by the US Food and Drug Administration. Conventional emulsion-based methods of manufacturing produce particles with a wide range of diameters (and thus kinetics of release) in each batch. This paper describes the fabrication of monodisperse, drug-loaded microparticles from biodegradable polymers using the microfluidic flow-focusing (FF) devices and the drug-delivery properties of those particles. Particles are engineered with defined sizes, ranging from 10 microm to 50 microm. These particles are nearly monodisperse (polydispersity index = 3.9%). A model amphiphilic drug (bupivacaine) is incorporated within the biodegradable matrix of the particles. Kinetic analysis shows that the release of the drug from these monodisperse particles is slower than that from conventional methods of the same average size but a broader distribution of sizes and, most importantly, exhibit a significantly lower initial burst than that observed with conventional particles. The difference in the initial kinetics of drug release is attributed to the uniform distribution of the drug inside the particles generated using the microfluidic methods. These results demonstrate the utility of microfluidic FF for the generation of homogenous systems of particles for the delivery of drugs.

Liquid‐Phase Exfoliation of Graphite Towards Solubilized Graphenes

Abstract: Following the astonishing discoveries of fullerenes and carbon nanotubes in earlier decades, the rise of graphene has recently triggered an exciting new area in the field of carbon nanoscience with continuously growing academic and technological impetus. Currently, several methods have been proposed to prepare graphenes, such as micromechanical cleavage, thermal annealing of SiC, chemical reduction of graphite oxide, intercalative expansion of graphite, bottom-up growth, chemical vapor deposition, and liquid-phase exfoliation. Especially this latter top-down approach is very appealing from a chemist’s point of view for the following reasons: i) it is direct, simple, and benign producing graphenes just by solvent treatment of graphite powders, and ii) the as-obtained sheets form colloidal dispersions in the solvents used for the exfoliation, thereby enabling their manipulation into various processes, like mixing, blending, casting, impregnation, spin-coating, or functionalization. The key parameter for suitable solvents is that the solvent–graphene interactions must be at least comparable to those existing between the stacked graphenes in graphite. To that end, Coleman and coworkers have successfully demonstrated this concept using N-methylpyrrolidone, N,N-dimethylacetamide, g-butyrolactone, 1,3-dimethyl-2-imidazolidinone, and benzyl benzoate as

A Facile and Novel Synthesis of Ag–Graphene-Based Nanocomposites

Abstract: Nanospacers for graphene: A facile and scalable process for the synthesis of aqueous solutions of isolated silver-decorated graphene sheets (see image) is presented. The silver–graphene nanocomposite film shows a 109-fold increase in electrical conductivity as compared to the graphite oxide film.

TiO2 nanotube surfaces: 15 nm--an optimal length scale of surface topography for cell adhesion and differentiation.

Abstract: Studies of biomimetic surfaces in medicine and biomaterial fields have explored extensively how the micrometer-scale topography of a surface controls cell behavior, but only recently has the nanoscale environment received attention as a critical factor for cell behavior. Several investigations of cell interactions have been performed using surface protrusion topographies at the nanoscale; such topographies are typically based on polymer demixing, ordered gold cluster arrays, or islands of adhesive ligands at distinct length scales. Recent work has indicated that the fabrication of ordered TiO2 nanotube layers with controlled diameters can be achieved by anodization of titanium in adequate electrolytes. Such surfaces can almost ideally be used as nanoscale spacing models for size-dependent cellular response. This is particularly important as these studies are carried out on titanium surfaces—a material used for clinical titanium implantations for the purpose of bone, joint, or tooth replacements. Therefore, principles elucidated from this work can guide implant surface modifications toward an optimized surface geometry and profile to best fit and cell interactions for adequate bone growth.

Protein‐Based Nanomedicine Platforms for Drug Delivery

Abstract: Protein-based nanomedicine platforms for drug delivery comprise naturally self-assembled protein subunits of the same protein or a combination of proteins making up a complete system. They are ideal for drug-delivery platforms due to their biocompatibility and biodegradability coupled with low toxicity. A variety of proteins have been used and characterized for drug-delivery systems, including the ferritin/apoferritin protein cage, plant-derived viral capsids, the small Heat shock protein (sHsp) cage, albumin, soy and whey protein, collagen, and gelatin. There are many different types and shapes that have been prepared to deliver drug molecules using protein-based platforms, including various protein cages, microspheres, nanoparticles, hydrogels, films, minirods, and minipellets. The protein cage is the most newly developed biomaterial for drug delivery and therapeutic applications. The uniform size, multifunctionality, and biodegradability push it to the frontier of drug delivery. In this Review, the recent strategic development of drug delivery is discussed with emphasis on polymer-based, especially protein-based, nanomedicine platforms for drug delivery. The advantages and disadvantages are also discussed for each type of protein-based drug-delivery system.

Mesoporous Silica Nanoparticles for Reducing Hemolytic Activity Towards Mammalian Red Blood Cells

Abstract: Recent reports on the design of silica-based nanomaterials, such as sol–gel, colloidal, and mesoporous silica nanoparticles (MSNs), have shown promising potential in utilizing these materials for controlled release, drug delivery, and other biotechnological applications. Several studies have demonstrated that the biocompatibility of these silica nanoparticles with a variety of cell types in vitro is fairly high. However, the low in vitro cytotoxicity offers no guarantee on the desired high biocompatibility in vivo. In fact, silica materials with amorphous particle morphology are known to cause the hemolysis of mammalian red blood cells (RBCs). This kind of hemolytic behavior raised serious bio-safety concerns regarding the application of amorphous silica for drug delivery involving intravenous administration and transport. Various explanations for the hemolytic effect have been proposed, including the generation of reactive oxygen species induced by the surface of silica, denaturation of membrane proteins through electrostatic interactions with silicate, and the high affinity of silicate for binding with the tetra-alkyl ammonium groups that are abundant in the membranes of RBCs. While the exact mechanism is still under investigation, most researchers agree that the hemolytic activity of silica is related to surface silanol groups. For example, a recent study by Murashov et al. demonstrated that the hemolytic activity of amorphous silica is proportional to the concentration of surface silanol groups of these solid materials. Given the fact that most, if not all, of the aforementioned silica nanoparticles with defined shapes and sizes also have abundant silanols on their surfaces, it is important to investigate the hemolytic properties of these materials with RBCs for potential intravenous applications. Herein, we describe an investigation of the hemolytic properties of a previously reported MSN material with mammalian

Particle Size, Surface Coating, and PEGylation Influence the Biodistribution of Quantum Dots in Living Mice

Abstract: This study evaluates the influence of particle size, PEGylation, and surface coating on the quantitative biodistribution of near-infrared-emitting quantum dots (QDs) in mice. Polymer- or peptide-coated 64Cu-labeled QDs 2 or 12 nm in diameter, with or without polyethylene glycol (PEG) of molecular weight 2000, are studied by serial micropositron emission tomography imaging and region-of-interest analysis, as well as transmission electron microscopy and inductively coupled plasma mass spectrometry. PEGylation and peptide coating slow QD uptake into the organs of the reticuloendothelial system (RES), liver and spleen, by a factor of 6-9 and 2-3, respectively. Small particles are in part renally excreted. Peptide-coated particles are cleared from liver faster than physical decay alone would suggest. Renal excretion of small QDs and slowing of RES clearance by PEGylation or peptide surface coating are encouraging steps toward the use of modified QDs for imaging living subjects.

Subjecting a Graphene Monolayer to Tension and Compression

Abstract: Themechanical behaviorof grapheneflakesunderboth tension and compression is examined using a cantilever-beam arrangement. Twodifferent sets of samples are employed.One consists of flakes just supported on a plastic bar. The other consists of flakesembeddedwithin theplastic substrate.Bymonitoring the shift of the 2DRaman linewith strain, information on the stress transfer efficiency as a function of stress sign and monolayer support are obtained. In tension, the embedded flake seems to sustain strains up to 1.3%, whereas in compression there is an indication of flake buckling at about 0.7% strain. The retainment of such a high critical buckling strain confirms the relative high flexural rigidity of the embedded monolayer. The mechanical strength and stiffness of crystalline materials are normally governed by the strength and stiffness

Nanostructured Silicon Anodes for Lithium Ion Rechargeable Batteries

Abstract: Rechargeable lithium ion batteries are integral to today's information-rich, mobile society. Currently they are one of the most popular types of battery used in portable electronics because of their high energy density and flexible design. Despite their increasing use at the present time, there is great continued commercial interest in developing new and improved electrode materials for lithium ion batteries that would lead to dramatically higher energy capacity and longer cycle life. Silicon is one of the most promising anode materials because it has the highest known theoretical charge capacity and is the second most abundant element on earth. However, silicon anodes have limited applications because of the huge volume change associated with the insertion and extraction of lithium. This causes cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity. Nanostructured silicon anodes, as compared to the previously tested silicon film anodes, can help overcome the above issues. As arrays of silicon nanowires or nanorods, which help accommodate the volume changes, or as nanoscale compliant layers, which increase the stress resilience of silicon films, nanoengineered silicon anodes show potential to enable a new generation of lithium ion batteries with significantly higher reversible charge capacity and longer cycle life.

Photoelectrochemical water splitting using dense and aligned TiO2 nanorod arrays.

Abstract: Dense and aligned TiO2 nanorod arrays are fabricated using oblique-angle deposition on indium tin oxide (ITO) conducting substrates. The TiO2 nanorods are measured to be 800-1100 nm in length and 45-400 nm in width with an anatase crystal phase. Coverage of the ITO is extremely high with 25 x 10(6) mm(-2) of the TiO2 nanorods. The first use of these dense TiO2 nanorod arrays as working electrodes in photoelectrochemical (PEC) cells used for the generation of hydrogen by water splitting is demonstrated. A number of experimental techniques including UV/Vis absorption spectroscopy, X-ray diffraction, high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, and photoelectrochemistry are used to characterize their structural, optical, and electronic properties. Both UV/Vis and incident-photon-to-current-efficiency measurements show their photoresponse in the visible is limited but with a marked increase around approximately 400 nm. Mott-Schottky measurements give a flat-band potential (V(FB)) of +0.20 V, a carrier density of 4.5 x 10(17) cm(-3), and a space-charge layer of 99 nm. Overall water splitting is observed with an applied overpotential at 1.0 V (versus Ag/AgCl) with a photo-to-hydrogen efficiency of 0.1%. The results suggest that these dense and aligned one-dimensional TiO2 nanostructures are promising for hydrogen generation from water splitting based on PEC cells.

Surface characteristics, copper release, and toxicity of nano- and micrometer-sized copper and copper(II) oxide particles: a cross-disciplinary study.

Abstract: An interdisciplinary and multianalytical research effort is undertaken to assess the toxic aspects of thoroughly characterized nano- and micrometer-sized particles of oxidized metallic copper and copper(II) oxide in contact with cultivated lung cells, as well as copper release in relevant media. All particles, except micrometer-sized Cu, release more copper in serum-containing cell medium (supplemented Dulbecco's minimal essential medium) compared to identical exposures in phosphate-buffered saline. Sonication of particles for dispersion prior to exposure has a large effect on the initial copper release from Cu nanoparticles. A clear size-dependent effect is observed from both a copper release and a toxicity perspective. In agreement with greater released amounts of copper per quantity of particles from the nanometer-sized particles compared to the micrometer-sized particles, the nanometer particles cause a higher degree of DNA damage (single-strand breaks) and cause a significantly higher percentage of cell death compared to cytotoxicity induced by micrometer-sized particles. Cytotoxic effects related to the released copper fraction are found to be significantly lower than the effects related to particles. No DNA damage is induced by the released copper fraction.

Nanoporous Polymers for Hydrogen Storage

Abstract: The design of hydrogen storage materials is one of the principal challenges that must be met before the development of a hydrogen economy. While hydrogen has a large specific energy, its volumetric energy density is so low as to require development of materials that can store and release it when needed. While much of the research on hydrogen storage focuses on metal hydrides, these materials are currently limited by slow kinetics and energy inefficiency. Nanostructured materials with high surface areas are actively being developed as another option. These materials avoid some of the kinetic and thermodynamic drawbacks of metal hydrides and other reactive methods of storing hydrogen. In this work, progress towards hydrogen storage with nanoporous materials in general and porous organic polymers in particular is critically reviewed. Mechanisms of formation for crosslinked polymers, hypercrosslinked polymers, polymers of intrinsic microporosity, and covalent organic frameworks are discussed. Strategies for controlling hydrogen storage capacity and adsorption enthalpy via manipulation of surface area, pore size, and pore volume are discussed in detail.

Synthesis of amphiphilic graphene nanoplatelets.

Abstract: Graphene, a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice, has attracted a great deal of attention in recent years for potential applications in many technological fields, such as nanoelectronics, nanocomposites, and hydrogen supercapacitors. One possible route to harnessing these properties would be to incorporate graphene sheets into composite materials. The manufacturing of such composites requires not only that the graphene sheets are produced on a sufficient scale, but also that they are incorporated, and homogeneously distributed, into various matrices. Graphite, which consists of a stack of flat graphene sheets, is available in large quantities from natural sources. It is likely the most readily available and least expensive source for the production of bulk graphene sheets. Graphite oxide (GO) is a layered material produced by the oxidation of graphite. In contrast to pristine graphite, the graphene-derived sheets in GO are heavily oxygenated and bear hydroxyl and epoxide functional groups on their basal planes, in addition to carbonyl and carboxyl groups located at the sheet edges. Unfortunately, owing to their hydrophilic nature, graphene oxide sheets can only be dispersed in aqueous media that are incompatible with most organic solvents and polymers. In addition, GO is electrically insulating, which limits its usefulness for the synthesis of composites. However, it has been demonstrated that the electrical conductivity of GO can be significantly increased and very thin graphene-like sheets can be obtained through the chemical reduction of exfoliated GO. Just like carbon nanotubes, a key challenge in the synthesis and processing of bulk-quantity graphene sheets is aggregation. Graphene sheets, due to their high specific surface area, tend to form irreversible agglomerates or even restack to form graphite through van der Waals interactions. As with carbon nanotubes, full utilization of graphene sheets in polymer nanocomposite applications will inevitably depend on their ability to achieve complete dispersion in the polymer matrix of choice.

Drug/dye-loaded, multifunctional iron oxide nanoparticles for combined targeted cancer therapy and dual optical/magnetic resonance imaging.

Abstract: A biocompatible, multimodal, and theranostic functional iron oxide nanoparticle is synthesized using a novel water-based method and exerts excellent properties for targeted cancer therapy, and optical and magnetic resonance imaging. For the first time, a facile, modified solvent diffusion method is used for the co-encapsulation of both an anticancer drug and near-infrared dyes. The resulting folate-derivatized theranostics nanoparticles could allow for targeted optical/magnetic resonance imaging and targeted killing of folate-expressing cancer cells.