Showing papers in "Small in 2010"

Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials.

Abstract: Isolated graphene, a nanometer-thick two-dimensional analog of fullerenes and carbon nanotubes, has recently sparked great excitement in the scientific community given its excellent mechanical and electronic properties. Particularly attractive is the availability of bulk quantities of graphene as both colloidal dispersions and powders, which enables the facile fabrication of many carbon-based materials. The fact that such large amounts of graphene are most easily produced via the reduction of graphene oxide--oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups--offers tremendous opportunities for access to functionalized graphene-based materials. Both graphene oxide and graphene can be processed into a wide variety of novel materials with distinctly different morphological features, where the carbonaceous nanosheets can serve as either the sole component, as in papers and thin films, or as fillers in polymer and/or inorganic nanocomposites. This Review summarizes techniques for preparing such advanced materials via stable graphene oxide, highly reduced graphene oxide, and graphene dispersions in aqueous and organic media. The excellent mechanical and electronic properties of the resulting materials are highlighted with a forward outlook on their applications.

Effect of Surface Properties on Nanoparticle–Cell Interactions

Abstract: The interaction of nanomaterials with cells and lipid bilayers is critical in many applications such as phototherapy, imaging, and drug/gene delivery. These applications require a firm control over nanoparticle-cell interactions, which are mainly dictated by surface properties of nanoparticles. This critical Review presents an understanding of how synthetic and natural chemical moieties on the nanoparticle surface (in addition to nanoparticle shape and size) impact their interaction with lipid bilayers and cells. Challenges for undertaking a systematic study to elucidate nanoparticle-cell interactions are also discussed.

Functional Graphene Oxide as a Nanocarrier for Controlled Loading and Targeted Delivery of Mixed Anticancer Drugs

Abstract: A simple synthetic route for the preparation of functional nanoscale graphene oxide (NGO), a novel nanocarrier for the loading and targeted delivery of anticancer drugs, is reported. The NGO is functionalized with sulfonic acid groups, which render it stable in physiological solution, followed by covalent binding of folic acid (FA) molecules to the NGO, thus allowing it to specifically target MCF-7 cells, human breast cancer cells with FA receptors. Furthermore, controlled loading of two anticancer drugs, doxorubicin (DOX) and camptothecin (CPT), onto the FA-conjugated NGO (FA-NGO) via pi-pi stacking and hydrophobic interactions is investigated. It is demonstrated that FA-NGO loaded with the two anticancer drugs shows specific targeting to MCF-7 cells, and remarkably high cytotoxicity compared to NGO loaded with either DOX or CPT only. Considering that the combined use of two or more drugs, a widely adopted clinical practice, often displays much better therapeutic efficacy than that of a single drug, the controlled loading and targeted delivery of mixed anticancer drugs using these graphene-based nanocarriers may find widespread application in biomedicine.

Fluorographene: A Two‐Dimensional Counterpart of Teflon

Abstract: A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives Fluorographene is a high-quality insulator (resistivity >10(12) Omega) with an optical gap of 3 eV It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15% Fluorographene is inert and stable up to 400 degrees C even in air, similar to Teflon

Biocompatibility, Biodistribution, and Drug-Delivery Efficiency of Mesoporous Silica Nanoparticles for Cancer Therapy in Animals

Abstract: Mesoporous silica nanoparticles (MSNs) are a promising material for drug delivery. In this Full Paper, MSNs are first shown to be well tolerated, as demonstrated by serological, hematological, and histopathological examinations of blood samples and mouse tissues after MSN injection. Biodistribution studies using human cancer xenografts are carried out with in vivo imaging and fluorescent microscopy imaging, as well as with inductively coupled plasma mass spectroscopy. The results show that MSNs preferentially accumulate in tumors. Finally, the drug-delivery capability of MSNs is demonstrated by following tumor growth in mice treated with camptothecin-loaded MSNs. These results indicate that MSNs are biocompatible, preferentially accumulate in tumors, and effectively deliver drugs to the tumors and suppress tumor growth.

High-concentration solvent exfoliation of graphene.

Abstract: A method is demonstrated to prepare graphene dispersions at high concentrations, up to 1.2 mg mL(-1), with yields of up to 4 wt% monolayers. This process relies on low-power sonication for long times, up to 460 h. Transmission electron microscopy shows the sonication to reduce the flake size, with flake dimensions scaling as t(-1/2). However, the mean flake length remains above 1 microm for all sonication times studied. Raman spectroscopy shows defects are introduced by the sonication process. However, detailed analysis suggests that predominantly edge, rather than basal-plane, defects are introduced. These dispersions are used to prepare high-quality free-standing graphene films. The dispersions can be heavily diluted by water without sedimentation or aggregation. This method facilitates graphene processing for a range of applications.

Mesoporous Silica Nanoparticles for Intracellular Controlled Drug Delivery

Abstract: The application of nanotechnology in the field of drug delivery has attracted much attention in the latest decades. Recent breakthroughs on the morphology control and surface functionalization of inorganic-based delivery vehicles, such as mesoporous silica nanoparticles (MSNs), have brought new possibilities to this burgeoning area of research. The ability to functionalize the surface of mesoporous-silica-based nanocarriers with stimuli-responsive groups, nanoparticles, polymers, and proteins that work as caps and gatekeepers for controlled release of various cargos is just one of the exciting results reported in the literature that highlights MSNs as a promising platform for various biotechnological and biomedical applications. This review focuses on the most recent progresses in the application of MSNs for intracellular drug delivery. The latest research on the pathways of entry into live mammalian and plant cells together with intracellular trafficking are described. One of the main areas of interest in this field is the development of site-specific drug delivery vehicles; the contribution of MSNs toward this topic is also summarized. In addition, the current research progress on the biocompatibility of this material in vitro and in vivo is discussed. Finally, the latest breakthroughs for intracellular controlled drug release using stimuli-responsive mesoporous-silica-based systems are described.

Fracture and fatigue in graphene nanocomposites

Abstract: Graphene, a single-atom-thick sheet of sp-bonded carbon atoms, has generatedmuch interest due to its high specific area and novel mechanical, electrical, and thermal properties. Recent advances in the production of bulk quantities of exfoliated graphene sheets from graphite have enabled the fabrication of graphene–polymer composites. Such composites show tremendous potential for mechanical-property enhancement due to their combination of high specific surface area, strong nanofiller–matrix adhesion and the outstanding mechanical properties of the sp carbon bonding network in graphene. Graphene fillers have been successfully dispersed in poly(styrene), poly(acrylonitrile) and poly(methyl methacrylate) matrices and the responses of their Young’s modulus, ultimate tensile strength, andglass-transition temperaturehave been characterized. However, to the best of our knowledge there is no report on the fracture toughness and fatigue properties of graphene–polymer composites. Fracture toughness describes the ability of a material containing a crack to resist fracture and it is a critically important material property for design applications. Fatigue involves dynamic propagation of cracks under cyclic loading and it is one of the primary causes of catastrophic failure in structural materials. Consequently, the material’s resistance to fracture and fatigue crack propagation are of paramount importance to prevent failure. Herein we report the fracture toughness, fracture energy, and fatigue properties of an epoxy polymer reinforced with various weight fractions of functionalized graphene sheets. Remarkably, only 0.125% weight of functionalized graphene sheets was observed to increase the fracture toughness of the pristine (unfilled) epoxy by 65% and the fracture energy by 115%.Toachievecomparableenhancement,carbonnanotube (CNT) and nanoparticle epoxy composites require one to two orders of magnitude larger weight fraction of nanofillers. Under fatigue conditions, incorporation of 0.125% weight of functionalized graphene sheets drastically reduced the rate of crack propagation in the epoxy 25-fold. Fractography analysis

Probing layer number and stacking order of few-layer graphene by Raman spectroscopy.

Abstract: Graphene is a two-dimensional material defined as a planar honeycomb lattice of close-packed carbon atoms, where the electrons exhibit a linear dispersion near Dirac K points and behave as massless Dirac fermions. However, the valence and conduction bands in an AB stacked graphene bilayer split into two parabolic branches near the K point originating from the interaction of p electrons, and the electrons are hence described by massive Dirac fermions. Moreover, a graphene bilayer is a tunable-gap semiconductor under electric-field biasing. With a further increase in the number of layers along with AB stacking, the electronic structure reveals stepwise variations that eventually approach that of the three-dimensional counterpart. Considering the close relation between the electronic properties and layer number of few-layer graphene (FLG), the ability to accurately determine the layer number and correlating this with the electronic structure is a prerequisite in understanding the evolution of the electronic properties from twoto threedimensional graphitic materials. In addition to graphene layers with AB stacking, FLG with arbitrary stacking (Figure 1) is considered to possess distinct properties arising from its different crystalline structure and p electron interactions. Experimentally, it has been observed that the electroand magnetotransport properties for folded graphene sheets are different to thoseofAB stackedbilayers. Furthermore,FLG grown on SiC, Ni, and Ru also have non-AB stacking order. Therefore, elucidating the detailed character-

Gold nanocages as photothermal transducers for cancer treatment.

Abstract: Gold nanocages represent a new class of nanomaterials with compact size and tunable optical properties for biomedical applications. They exhibit strong light absorption in the near-infrared region in which light can penetrate deeply into soft tissue. After PEGylation, the Au nanocages can be passively delivered to tumors in animals. Analysis of tissue distribution for the PEGylated Au nanocages showed that the tumor uptake was 5.7 %ID/g at 96 h post injection. The Au nanocages were found not only on the surface, but also in the core of the tumor. By exposing tumors to a near-infrared diode laser (0.7 W/cm2, CW, λ=808 nm) for 10 min, the photothermal effect of the Au nanocages could selectively destroy tumor tissue with minimum damage to the surrounding healthy tissue. Data from functional [18F]fluorodexoyglucose positron emission tomography revealed a decrease in tumor metabolic activity upon the photothermal treatment. Histological examination identified extensive damage to the nuclei of tumor cells and tumor interstitium.

Electrochemical deposition of ZnO nanorods on transparent reduced graphene oxide electrodes for hybrid solar cells.

Abstract: Monocrystalline ZnO nanorods (NRs) with high donor concentration are electrochemically deposited on highly conductive reduced graphene oxide (rGO) films on quartz. The film thickness, optical transmittance, sheet resistance, and roughness of rGO films are systematically studied. The obtained ZnO NRs on rGO films are characterized by X-ray diffraction, transmission electron microscopy, photoluminescence, and Raman spectra. As a proof-of-concept application, the obtained ZnO NRs on rGO are used to fabricate inorganic-organic hybrid solar cells with layered structure of quartz/rGO/ZnO NR/poly(3-hexylthiophene)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (P3HT/PEDOT:PSS)/Au. The observed power conversion efficiency (PCE, eta), approximately 0.31%, is higher than that reported in previous solar cells by using graphene films as electrodes. These results clearly demonstrate that rGO films with a higher conductivity have a smaller work function and show a better performance in the fabricated solar cells.

Small upconverting fluorescent nanoparticles for biomedical applications.

Abstract: Fluorescent labels have been widely used for biological applications, primarily in imaging and assays. Traditional fluorophores such as fluorescent dyes are mainly based on downconversion fluorescence, which have several drawbacks such as photobleaching, high background noise from autofluorescence, and considerable photodamage to biological materials. Upconverting fluorescent nanoparticles emit detectable photons of higher energy in the near-infrared (NIR) or visible range upon irradiation with an NIR light in a process termed 'upconversion.' They overcome some of the disadvantages faced by conventional downconversion labels, thus making them an ideal fluorescent label for biological applications. This review looks at the development of these particles, critically examines the reported applications, and discusses their future in biomedicine.

Understanding the Photothermal Conversion Efficiency of Gold Nanocrystals

Abstract: Plasmon-based photothermal therapy is one of the most intriguing applications of noble metal nanostructures. The photothermal conversion efficiency is an essential parameter in practically realizing this application. The effects of the plasmon resonance wavelength, particle volume, shell coating, and assembly on the photothermal conversion efficiencies of Au nanocrystals are systematically studied by directly measuring the temperature of Au nanocrystal solutions with a thermocouple and analyzed on the basis of energy balance. The temperature of Au nanocrystal solutions reaches the maximum at ∼75 °C when the plasmon resonance wavelength of Au nanocrystals is equal to the illumination laser wavelength. For Au nanocrystals with similar shapes, the larger the nanocrystal, the smaller the photothermal conversion efficiency becomes. The photothermal conversion can also be controlled by shell coating and assembly through the change in the plasmon resonance energy of Au nanocrystals. Moreover, coating Au nanocrystals with semiconductor materials that have band gap energies smaller than the illumination laser energy can improve the photothermal conversion efficiency owing to the presence of an additional light absorption channel.

SERS-based diagnosis and biodetection.

Abstract: Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most powerful analytical techniques for identification of molecular species, with the potential to reach single-molecule detection under ambient conditions. This Concept article presents a brief introduction and discussion of both recent advances and limitations of SERS in the context of diagnosis and biodetection, ranging from direct sensing to the use of encoded nanoparticles, in particular focusing on ultradetection of relevant bioanalytes, rapid diagnosis of diseases, marking of organelles within individual cells, and non-invasive tagging of anomalous tissues in living animals.

Graphene Fluoride: A Stable Stoichiometric Graphene Derivative and its Chemical Conversion to Graphene

Abstract: Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.

In vivo quantum-dot toxicity assessment

Abstract: Quantum dots have potential in biomedical applications, but concerns persist about their safety. Most toxicology data is derived from in vitro studies and may not reflect in vivo responses. Here, an initial systematic animal toxicity study of CdSe-ZnS core-shell quantum dots in healthy Sprague-Dawley rats is presented. Biodistribution, animal survival, animal mass, hematology, clinical biochemistry, and organ histology are characterized at different concentrations (2.5-15.0 nmol) over short-term ( 80 days) periods. The results show that the quantum dot formulations do not cause appreciable toxicity even after their breakdown in vivo over time. To generalize the toxicity of quantum dots in vivo, further investigations are still required. Some of these investigations include the evaluation of quantum dot composition (e.g., PbS versus CdS), surface chemistry (e.g., functionalization with amines versus carboxylic acids), size (e.g., 2 versus 6 nm), and shape (e.g., spheres versus rods), as well as the effect of contaminants and their byproducts on biodistribution behavior and toxicity. Combining the results from all of these studies will eventually lead to a conclusion regarding the issue of quantum dot toxicity.

Flexible, transparent, conducting films of randomly stacked graphene from surfactant-stabilized, oxide-free graphene dispersions.

Abstract: Graphite is exfoliated in water to give dispersions of mono- and few-layer graphene stabilized by surfactant. These dispersions can be used to form thin, disordered films of randomly stacked, oxide-free, few-layer graphenes. These films are transparent with a direct current conductivity of up to 1.5 x 10(4) S m(-1). The conductivity is stable under flexing for at least 2000 cycles. The electrical properties are limited by disorder and aggregation suggesting future routes for improvement.

Conducting‐Polymer Nanotubes Improve Electrical Properties, Mechanical Adhesion, Neural Attachment, and Neurite Outgrowth of Neural Electrodes

Abstract: An in vitro comparison of conducting-polymer nanotubes of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) and to their film counterparts is reported. Impedance, charge-capacity density (CCD), tendency towards delamination, and neurite outgrowth are compared. For the same deposition charge density, PPy films and nanotubes grow relatively faster vertically, while PEDOT films and nanotubes grow more laterally. For the same deposition charge density (1.44 C cm(-2)), PPy nanotubes and PEDOT nanotubes have lower impedance (19.5 +/- 2.1 kOmega for PPy nanotubes and 2.5 +/- 1.4 kOmega for PEDOT nanotubes at 1 kHz) and higher CCD (184 +/- 5.3 mC cm(-2) for PPy nanotubes and 392 +/- 6.2 mC cm(-2) for PEDOT nanotubes) compared to their film counterparts. However, PEDOT nanotubes decrease the impedance of neural-electrode sites by about two orders of magnitude (bare iridium 468.8 +/- 13.3 kOmega at 1 kHz) and increase capacity of charge density by about three orders of magnitude (bare iridium 0.1 +/- 0.5 mC cm(-2)). During cyclic voltammetry measurements, both PPy and PEDOT nanotubes remain adherent on the surface of the silicon dioxide while PPy and PEDOT films delaminate. In experiments of primary neurons with conducting-polymer nanotubes, cultured dorsal root ganglion explants remain more intact and exhibit longer neurites (1400 +/- 95 microm for PPy nanotubes and 2100 +/- 150 microm for PEDOT nanotubes) than their film counterparts. These findings suggest that conducting-polymer nanotubes may improve the long-term function of neural microelectrodes.

Constraint of DNA on Functionalized Graphene Improves its Biostability and Specificity

Abstract: The single-stranded DNA constrained on graphene surface is effectively protected from enzymatic cleavage by DNase I. The anisotropy, fluorescence, NMR, and CD studies suggest that the single-stranded DNA is promptly adsorbed onto graphene forming strong molecular interactions. Furthermore, the constraint of DNA probe on graphene improves the specificity of its response to complementary DNA. These findings will promote the further application of graphene in biotechnology and biomedical fields.

Rattle-type Fe(3)O(4)@SiO(2) hollow mesoporous spheres as carriers for drug delivery.

Abstract: Rattle-type Fe(3)O(4)@SiO(2) hollow mesoporous spheres with different particle sizes, different mesoporous shell thicknesses, and different levels of Fe(3)O(4) content are prepared by using carbon spheres as templates. The effects of particle size and concentration of Fe(3)O(4)@SiO(2) hollow mesoporous spheres on cell uptake and their in vitro cytotoxicity to HeLa cells are evaluated. The spheres exhibit relatively fast cell uptake. Concentrations of up to 150 microg mL(-1) show no cytotoxicity, whereas a concentration of 200 microg mL(-1) shows a small amount of cytotoxicity after 48 h of incubation. Doxorubicin hydrochloride (DOX), an anticancer drug, is loaded into the Fe(3)O(4)@SiO(2) hollow mesoporous spheres, and the DOX-loaded spheres exhibit a somewhat higher cytotoxicity than free DOX. These results indicate the potential of Fe(3)O(4)@SiO(2) hollow mesoporous spheres for drug loading and delivery into cancer cells to induce cell death.

Nanowire-Based Sensors

Abstract: Nanowires are important potential candidates for the realization of the next generation of sensors. They offer many advantages such as high surface-to-volume ratios, Debye lengths comparable to the target molecule, minimum power consumption, and they can be relatively easily incorporated into microelectronic devices. Accordingly, there has been an intensified search for novel nanowire materials and corresponding platforms for realizing single-molecule detection with superior sensing performance. In this work, progress made towards the use of nanowires for achieving better sensing performance is critically reviewed. In particular, various nanowires types (metallic, semiconducting, and insulating) and their employment either as a sensor material or as a template material are discussed. Major obstacles and future steps towards the ultimate nanosensors based on nanowires are addressed.

Morphology-Controlled Synthesis of SnO 2 Nanotubes by Using 1D Silica Mesostructures as Sacrificial Templates and Their Applications in Lithium-Ion Batteries

Abstract: SnO(2) nanotubes with controllable morphologies are successfully synthesized by using a variety of one-dimensional (1D) silica mesostructures as effective sacrificial templates. Firstly, 1D silica mesostructures with different morphologies, such as chiral nanorods, nonchiral nanofibers, and helical nanotubes, are readily synthesized in aqueous solution by using the triblock copolymer Pluronic F127 and the cationic surfactant cetyltrimethylammonium bromide as binary templates. Subsequently, the obtained 1D silica mesostructures are used as sacrificial templates to synthesize SnO(2) nanotubes with preserved morphologies via a simple hydrothermal route, resulting in the formation of well-defined SnO(2) nanotubes with different lengths and unique helical SnO(2) nanotubes with a wealth of conformations. It is revealed that both of the short and long SnO(2) nanotubes showed much better performance as anode materials in lithium-ion batteries than normal SnO(2) nanopowders, which might be related to the hollow structure of the nanotubes that could alleviate the volume changes and mechanical stress during charging/discharging cycling. Moreover, the capacity and cycling performance of short nanotubes, which showed a specific discharge capacity of 468 mAh g(-1) after 30 cycles, are considerably better than those of long nanotubes because of the more robust structure of the short nanotubes.

Porous Graphene as an Atmospheric Nanofilter

Abstract: The fabrication of nanoscale membranes exhibiting high selectivity is an emerging field of research. The possibility to use bottom-up approaches to fabricate a filter with porous graphene and analyze its functionality with first principle calculations is investigated. Here, the porous network is produced by self-assembly of the hexaiodo-substituted macrocycle cyclohexa-m-phenylene (CHP). The resulting porous network exhibits an extremely high selectivity in favor of H(2) and He among other atmospheric gases, such as Ne, O(2), N(2), CO, CO(2), NH(3), and Ar. The presented membrane is superior to traditional filters using polymers or silica and could have great potential for further technological applications such as gas sensors or fuel cells.

Flexible Piezoelectric ZnO–Paper Nanocomposite Strain Sensor

Abstract: The fabrication of a mechanically flexible, piezoelectric nanocomposite material for strain sensing applications is reported. Nanocomposite material consisting of zinc oxide (ZnO) nanostructures embedded in a stable matrix of paper (cellulose fibers) is prepared by a solvothermal method. The applicability of this material as a strain sensor is demonstrated by studying its real-time current response under both static and dynamic mechanical loading. The material presented highlights a novel approach to introduce flexibility into strain sensors by embedding crystalline piezoelectric material in a flexible cellulose-based secondary matrix.

Quantitative evaluation of cellular uptake and trafficking of plain and polyethylene glycol-coated gold nanoparticles.

Abstract: This study addresses the cellular uptake and intracellular trafficking of 15-nm gold nanoparticles (NPs), either plain (i.e., stabilized with citrate) or coated with polyethylene glycol (PEG), exposed to human alveolar epithelial cells (A549) at the air-liquid interface for 1, 4, and 24 h. Quantitative analysis by stereology on transmission electron microscopy images reveals a significant, nonrandom intracellular distribution for both NP types. No particles are observed in the nucleus, mitochondria, endoplasmic reticulum, or golgi. The cytosol is not a preferred cellular compartment for both NP types, although significantly more PEG-coated than citrate-stabilized NPs are present there. The preferred particle localizations are vesicles of different sizes ( 1000 nm). This is observed for both NP types and indicates a predominant uptake by endocytosis. Subsequent inhibition of caveolin- and clathrin-mediated endocytosis by methyl-beta-cyclodextrin (MbetaCD) results in a significant reduction of intracellular NPs. The inhibition, however, is more pronounced for PEG-coated than citrate-stabilized NPs. The latter are mostly found in larger vesicles; therefore, they are potentially taken up by macropinocytosis, which is not inhibited by MbetaCD. With prolonged exposure times, both NPs are preferentially localized in larger-sized intracellular vesicles such as lysosomes, thus indicating intracellular particle trafficking. This quantitative evaluation reveals that NP surface coatings modulate endocytotic uptake pathways and cellular NP trafficking. Other nonendocytotic entry mechanisms are found to be involved as well, as indicated by localization of a minority of PEG-coated NPs in the cytosol.

Layer‐By‐Layer‐Assembled Capsules and Films for Therapeutic Delivery

Abstract: Polymeric materials formed via layer-by-layer (LbL) assembly have promise for use as drug delivery vehicles. These multilayered materials, both as capsules and thin fi lms, can encapsulate a high payload of toxic or sensitive drugs, and can be readily engineered and functionalized with specific properties. This review highlights important and recent studies that advance the use of LbL-assembled materials as therapeutic devices. It also seeks to identify areas that require additional investigation for future development of the field. A variety of drug-loading methods and delivery routes are discussed. The biological barriers to successful delivery are identified, and possible solutions to these problems are discussed. Finally, state-of-the-art degradation and cargo release mechanisms are also presented.

The effects of size, shape, and surface functional group of gold nanostructures on their adsorption and internalization by cells.

Abstract: In this study, we examined the effects of size, shape, and surface chemistry of gold nanostructures on their uptake (including both adsorption and internalization) by SK-BR-3 breast cancer cells. We used both spherical and cubic Au nanostructures (nanospheres and nanocages, respectively) of two different sizes, and their surface was modified with poly(ethylene glycol) (PEG), antibody anti-HER2, or poly(allyamine hydrochloride) (PAA). Our results showed that the size of the Au nanostructures influenced their uptake by the cells in a similar way regardless of the surface chemistry, while the shape dependency could vary depending on the surface functional group. In addition, the cells preferred to take up the Au nanostructures covered by different surface groups in the following order: PAA>> anti-HER2> PEG. The fraction of Au nanostructures attached to the cell surface was also dependent on the aforementioned parameters.

Tunable bandgap in graphene by the controlled adsorption of water molecules.

Abstract: Graphene, a single-atom-thick layer of sp 2 -hybridized carbon atoms, has generated considerable excitement in the scientifi c community due to its peculiar electronic band structure, which leads to unusual phenomena such as the anomalous quantum Hall effect, [ 1,2 ] spin-resolved quantum interference, [ 3 ] ballistic electron transport, [ 4 ] and bipolar supercurrent. [ 5 ] However, pristine graphene is a semimetal with zero bandgap; the local density of states at the Fermi level is zero and conduction can only occur by the thermal excitation of electrons. [ 2 ] This lack of an electronic bandgap is the major obstacle limiting the utilization of graphene in nano-electronic and -photonic devices, [ 6,7 ] such as p–n junctions, transistors, photodiodes, and lasers. The graphene band structure is sensitive to lattice symmetry and several methods have been developed to break this symmetry and open an energy gap. These methods are based on a variety of techniques, such as defect generation, [ 8 ] doping (e.g., with potassium [ 9 ] ), applied bias, [ 10–12 ] and interaction with gases [ 13 ] (e.g., nitrogen dioxide). For instance, in reference [ 12 ] a tunable bandgap of up to 0.25 eV was achieved for electrically gated bilayer graphene by a variable external electric fi eld. Similarly, an internal electric fi eld produced by an imbalance of doped charge between two graphene layers has been shown to open a bandgap. [ 9 ] It has been demonstrated that a gap of ≈ 0.26 eV can be produced by growing graphene epitaxially on silicon carbide substrates. [ 14 ] This gap originated from the breaking of sublattice symmetry due to the graphene–substrate interaction. Patterned adsorption of atomic hydrogen onto the Moire superlattice positions of graphene [ 15 ] has resulted in a bandgap of ≈ 0.73 eV opening, while half-hydrogenated graphene [ 16 ] resulted in a bandgap of ≈ 0.43 eV. A graphene nanomesh structure [ 17 ] has also been shown to exhibit a bandgap. In this graphene structure, lateral quantum confi nement and localization effects due to

Controlling Cell Behavior Through the Design of Polymer Surfaces

Abstract: Polymers have gained a remarkable place in the biomedical field as materials for the fabrication of various devices and for tissue engineering applications. The initial acceptance or rejection of an implantable device is dictated by the crosstalk of the material surface with the bioentities present in the physiological environment. Advances in microfabrication and nanotechnology offer new tools to investigate the complex signaling cascade induced by the components of the extracellular matrix and consequently allow cellular responses to be tailored through the mimicking of some elements of the signaling paths. Patterning methods and selective chemical modification schemes at different length scales can provide biocompatible surfaces that control cellular interactions on the micrometer and sub-micrometer scales on which cells are organized. In this review, the potential of chemically and topographically structured micro- and nanopolymer surfaces are discussed in hopes of a better understanding of cell-biomaterial interactions, including the recent use of biomimetic approaches or stimuli-responsive macromolecules. Additionally, the focus will be on how the knowledge obtained using these surfaces can be incorporated to design biocompatible materials for various biomedical applications, such as tissue engineering, implants, cell-based biosensors, diagnostic systems, and basic cell biology. The review focusses on the research carried out during the last decade.