Graphene-hBN non-van der Waals vertical heterostructures for four- electron oxygen reduction reaction.

A novel vertical non-van der Waals (non-vdW) heterostructure of graphene and hexagonal boron nitride (G/hBN) is realized and its application in direct four-electron oxygen reduction reaction (ORR) in alkaline medium is established. The G/hBN differs from previously demonstrated vdW heterostructures, where it has a chemical bridging between graphene and hBN allowing a direct charge transfer - resulting in high ORR activity. The ORR efficacy of G/hBN is compared with that of graphene-hBN vdW structure and individual layers of graphene and hBN along with that of benchmark platinum/carbon (Pt/C). The ORR activity of G/hBN is found to be on par with Pt/C in terms of current density but with much higher electrochemical stability and methanol tolerance. The onset potential of the G/hBN is found to be improved from 780 mV at a glassy carbon electrode to 930 mV and 940 mV in gold and platinum electrodes, respectively, indicating its substrate-dependent catalytic activity. This opens possibilities of new benchmark catalysts of metals capped with G/hBN atomic layers, where the underneath metal is protected while keeping the activity similar to that of pristine metal. Density functional theory-based calculations are found to be supporting the observed augmented ORR performance of G/hBN.

Biocorona formation contributes to silver nanoparticle induced endoplasmic reticulum stress.

Prior research has demonstrated cells exposed to silver nanoparticles (AgNPs) undergo endoplasmic reticulum (ER) stress leading to cellular apoptosis and toxicity, however, the fundamental mechanism underlying AgNP-induced ER stress is unknown. We hypothesize the biophysical interactions between AgNPs and adsorbed proteins lead to misfolded proteins to elicit an ER stress response. Our investigation examined rat aortic endothelial cells (RAEC) exposed to 20 or 100 nm AgNPs with or without a biocorona (BC) consisting of bovine serum albumin (BSA), high density lipoprotein (HDL) or fetal bovine serum (FBS) to form a complex BC. The presence of a BC consisting of BSA or FBS proteins significantly reduced uptake of 20 nm and 100 nm AgNPs in RAEC. Western blot analysis indicated robust activation of the IREα and PERK pathways in RAEC exposed to 20 nm despite the reduction in uptake by the presence of a BC. This was not observed for the 100 nm AgNPs. Hyperspectral darkfield microscopy qualitatively confirmed that the preformed BC was maintained following uptake by RAEC. Transmission electron microscopy demonstrated a size dependent effect on the sub-cellular localization of AgNPs. Overall, these results suggest that AgNP size, surface area and BC formation governs the induction of ER stress and alterations in intracellular trafficking.

Impact absorption properties of carbon fiber reinforced bucky sponges.

We describe the super compressible and highly recoverable response of bucky sponges as they are struck by a heavy flat-punch striker. The bucky sponges studied here are structurally stable, self-assembled mixtures of multiwalled carbon nanotubes (MWCNTs) and carbon fibers (CFs). We engineered the microstructure of the sponges by controlling their porosity using different CF contents. Their mechanical properties and energy dissipation characteristics during impact loading are presented as a function of their composition. The inclusion of CFs improves the impact force damping by up to 50% and the specific damping capacity by up to 7% compared to bucky sponges without CFs. The sponges also exhibit significantly better stress mitigation characteristics compared to vertically aligned CNT foams of similar densities. We show that delamination occurs at the MWCNT-CF interfaces during unloading, and it arises from the heterogeneous fibrous microstructure of the bucky sponges.

C60 as an active smart spacer material on silver thin film substrates for enhanced surface plasmon coupled emission.

In this study, we present the use of C60 as an active spacer material on a silver (Ag) based surface plasmon coupled emission (SPCE) platform. In addition to its primary role of protecting the Ag thin film from oxidation, the incorporation of C60 facilitated the achievement of a 30-fold enhancement in the emission intensity of rhodamine B (RhB) fluorophore. The high signal yield was attributed to the unique π-π interactions between C60 thin films and RhB, which enabled efficient transfer of energy of RhB emission to Ag plasmon modes. Furthermore, minor variations in the C60 film thickness yielded large changes in the enhancement and angularity properties of the SPCE signal, which can be exploited for sensing applications. Finally, the low-cost fabrication process of the Ag-C60 thin film stacks render C60 based SPCE substrates ideal, for the economic and simplistic detection of analytes.

Flexible Ag-C60 nano-biosensors based on surface plasmon coupled emission for clinical and forensic applications.

The relatively low sensitivity of fluorescence detection schemes, which are mainly limited by the isotropic nature of fluorophore emission, can be overcome by utilizing surface plasmon coupled emission (SPCE). In this study, we demonstrate directional emission from fluorophores on flexible Ag-C60 SPCE sensor platforms for point-of-care sensing, in healthcare and forensic sensing scenarios, with at least 10 times higher sensitivity than traditional fluorescence sensing schemes. Adopting the highly sensitive Ag-C60 SPCE platform based on glass and novel low-cost flexible substrates, we report the unambiguous detection of acid-fast Mycobacterium tuberculosis (Mtb) bacteria at densities as low as 20 Mtb mm(-2); from non-acid-fast bacteria (e.g., E. coli and S. aureus), and the specific on-site detection of acid-fast sperm cells in human semen samples. In combination with the directional emission and high-sensitivity of SPCE platforms, we also demonstrate the utility of smartphones that can replace expensive and cumbersome detectors to enable rapid hand-held detection of analytes in resource-limited settings; a much needed critical advance to biosensors, for developing countries.

Tomato Seed Coat Permeability to Selected Carbon Nanomaterials and Enhancement of Germination and Seedling Growth.

Seed coat permeability was examined using a model that tested the effects of soaking tomato (Solanum lycopersicon) seeds in combination with carbon-based nanomaterials (CBNMs) and ultrasonic irradiation (US). Penetration of seed coats to the embryo by CBNMs, as well as CBNMs effects on seed germination and seedling growth, was examined. Two CBNMs, C60(OH)20 (fullerol) and multiwalled nanotubes (MWNTs), were applied at 50 mg/L, and treatment exposure ranged from 0 to 60 minutes. Bright field, fluorescence, and electron microscopy and micro-Raman spectroscopy provided corroborating evidence that neither CBNM was able to penetrate the seed coat. The restriction of nanomaterial (NM) uptake was attributed to the semipermeable layer located at the innermost layer of the seed coat adjacent to the endosperm. Seed treatments using US at 30 or 60 minutes in the presence of MWNTs physically disrupted the seed coat; however, the integrity of the semipermeable layer was not impaired. The germination percentage and seedling length and weight were enhanced in the presence of MWNTs but were not altered by C60(OH)20. The combined exposure of seeds to NMs and US provided insight into the nanoparticle-seed interaction and may serve as a delivery system for enhancing seed germination and early seedling growth.

The role of defects in the nonlinear optical absorption behavior of carbon and ZnO nanostructures.

In bulk materials, defects are usually considered to be unwanted since deviations from perfect lattices may degrade device performance. Interestingly, the presence of defects throws open new possibilities in the case of nanostructures due to the properties related to their limited size scale. Defects and disorders which alter the electronic structure of nanostructures can significantly influence their electronic, magnetic and nonlinear optical properties. Here, we show that defect engineering is an effective strategy for tailoring the nonlinear optical (NLO) properties of carbon and ZnO nanostructures. The effects of surface states, lattice disorders, polycrystalline interfaces and heterogeneous dopants on the nonlinear absorption behaviour of these nanostructures are discussed in detail. Realistic tunable NLO features achieved by controlling such defects enhance the scope of these nanostructures in device applications such as optical limiting, optical switching, pulse shaping, pulse compression and optical diode action.

Optical diode action from axially asymmetric nonlinearity in an all-carbon solid-state device.

Nanostructured carbons are posited to offer an alternative to silicon and lead to further miniaturization of photonic and electronic devices. Here, we report the experimental realization of the first all-carbon solid-state optical diode that is based on axially asymmetric nonlinear absorption in a thin saturable absorber (graphene) and a thin reverse saturable absorber (C60) arranged in tandem. This all-optical diode action is polarization independent and has no phase-matching constraints. The nonreciprocity factor of the device can be tuned by varying the number of graphene layers and the concentration or thickness of the C60 coating. This ultracompact graphene/C60 based optical diode is versatile with an inherently large bandwidth, chemical and thermal stability, and is poised for cost-effective large-scale integration with existing fabrication technologies.

Nanobiotechnology can boost crop production and quality: first evidence from increased plant biomass, fruit yield and phytomedicine content in bitter melon (Momordica charantia).

BACKGROUND: Recent research on nanoparticles in a number of crops has evidenced for enhanced germination and seedling growth, physiological activities including photosynthetic activity and nitrogen metabolism, mRNA expression and protein level, and also positive changes in gene expression indicating their potential use in crop improvement. We used a medicinally rich vegetable crop, bitter melon, as a model to evaluate the effects of seed treatment with a carbon-based nanoparticle, fullerol [C60(OH)20], on yield of plant biomass and fruit characters, and phytomedicine contents in fruits. RESULTS: We confirmed the uptake, translocation and accumulation of fullerol through bright field imaging and Fourier transform infra-red spectroscopy. We observed varied effects of seed treatment at five concentrations, including non-consequential and positive, on plant biomass yield, fruit yield and its component characters, and content of five phytomedicines in fruits. Fullerol-treatment resulted in increases up to 54% in biomass yield and 24% in water content. Increases of up to 20% in fruit length, 59% in fruit number, and 70% in fruit weight led to an improvement up to 128% in fruit yield. Contents of two anticancer phytomedicines, cucurbitacin-B and lycopene, were enhanced up to 74% and 82%, respectively, and contents of two antidiabetic phytomedicines, charantin and insulin, were augmented up to 20% and 91%, respectively. Non-significant correlation inter se plant biomass, fruit yield, phytomedicine content and water content evidenced for separate genetic control and biosynthetic pathways for production of plant biomass, fruits, and phytomedicines in fruits, and also no impact of increased water uptake. CONCLUSIONS: While our results indicated possibility of improving crop yield and quality by using proper concentrations of fullerol, extreme caution needs to be exercised given emerging knowledge about accumulation and toxicity of nanoparticles in bodily tissues.

Toxicity of engineered nanomaterials: a physicochemical perspective.

The global market for nanomaterial-based products is forecasted to reach 100 billion dollars per annum for 2011-2015. Extensive manufacturing and the use of engineered nanomaterials have raised concerns regarding their impact on biological response in living organisms and the environment at large. The fundamental properties of nanomaterials exhibit a complex dependence upon several factors such as their morphology, size, defects, and chemical stability. Therefore, it is exceedingly difficult to correlate their biological response with their intricate physicochemical properties. For example, varying toxic response may ensue due to different methods of nanomaterial preparation, dissimilar impurities, and defects. In this review, we surveyed the existing literature on the dependence of cytotoxicity on physicochemical properties. We found that ENM size, shape, defect density, physicochemical stability, and surface modification to be the main causes that elicit altered physiological response or cytotoxicity.

Insights into the Pseudocapacitive Behavior of Sulfurized Polymer Electrodes for Li-S Batteries.

Practical applications of sulfurized polymer (SP) materials in Li-S batteries (LSBs) are often written off due to their low S content (≈35 wt%). Unlike conventional S8 /C composite cathodes, SP materials are shown to function as pseudocapacitors with an active carbon backbone using a comprehensive array of tools including in situ Raman and electrochemical impedance spectroscopy. Critical metric analysis of LSBs containing SP materials with an active carbon skeleton shows that SP cathodes with 35 wt% S are suitable for 350 Wh kg-1 target at the cell level if S loading >5 mg cm-2 , electrolyte-to-sulfur ratio <2 µL mg-1 , and negative-to-positive ratio <5 can be achieved. Although 3D current collectors can enable such high loadings, they often add excess mass decreasing the total capacity. An "active" carbon nanotube bucky sandwich current collector developed here offsets its excess weight by contributing to the electric double layer capacity. SP cathodes (35 wt% S) with ≈5.5 mg cm-2 of S loading (≈15.8 mg cm-2 of SP loading) yield a sulfur-level gravimetric capacity ≈1360 mAh gs -1 (≈690 mAh gs -1 ), electrode level capacity 200 mAh gelectrode -1 (100 mAh gelectrode -1 ), and areal capacity ≈7.8 mAh cm-2 (≈4.0 mAh cm-2 ) at 0.1C (1C) rate for ≈100 cycles at E/S ratio = 7 µL mg-1 .

A carbon nanotube toxicity paradigm driven by mast cells and the IL-33/ST2 axis.

Concern about the use of nanomaterials has increased significantly in recent years due to potentially hazardous impacts on human health. Mast cells are critical for innate and adaptive immune responses, often modulating allergic and pathogenic conditions. Mast cells are well known to act in response to danger signals through a variety of receptors and pathways including IL-33 and the IL-1-like receptor ST2. Here, the involvement of mast cells and the IL-33/ST2 axis in pulmonary and cardiovascular responses to multi-walled carbon nanotube (MWCNT) exposure are examined. Toxicological effects of MWCNTs are observed only in mice with a sufficient population of mast cells and are not observed when mast cells are absent or incapable of responding to IL-33. Our findings establish for the first time that mast cells and the IL-33/ST2 axis orchestrates adverse pulmonary and cardiovascular responses to an engineered nanomaterial, giving insight into a previously unknown mechanism of toxicity. This novel mechanism of toxicity could be used for assessing the safety of engineered nanomaterials and provides a realistic therapeutic target for potential nanoparticle induced toxicities.

Expansion of cardiac ischemia/reperfusion injury after instillation of three forms of multi-walled carbon nanotubes.

BACKGROUND: The exceptional physical-chemical properties of carbon nanotubes have lead to their use in diverse commercial and biomedical applications. However, their utilization has raised concerns about human exposure that may predispose individuals to adverse health risks. The present study investigated the susceptibility to cardiac ischemic injury following a single exposure to various forms of multi-walled carbon nanotubes (MWCNTs). It was hypothesized that oropharyngeal aspiration of MWCNTs exacerbates myocardial ischemia and reperfusion injury (I/R injury). METHODS: Oropharyngeal aspiration was performed on male C57BL/6J mice with a single amount of MWCNT (0.01 - 100 µg) suspended in 100 µL of a surfactant saline (SS) solution. Three forms of MWCNTs were used in this study: unmodified, commercial grade (C-grade), and functionalized forms that were modified either by acid treatment (carboxylated, COOH) or nitrogenation (N-doped) and a SS vehicle. The pulmonary inflammation, serum cytokine profile and cardiac ischemic/reperfusion (I/R) injury were assessed at 1, 7 and 28 days post-aspiration. RESULTS: Pulmonary response to MWCNT oropharyngeal aspiration assessed by bronchoalveolar lavage fluid (BALF) revealed modest increases in protein and inflammatory cell recruitment. Lung histology showed modest tissue inflammation as compared to the SS group. Serum levels of eotaxin were significantly elevated in the carboxylated MWCNT aspirated mice 1 day post exposure. Oropharyngeal aspiration of all three forms of MWCNTs resulted in a time and/or dose-dependent exacerbation of myocardial infarction. The severity of myocardial injury varied with the form of MWCNTs used. The N-doped MWCNT produced the greatest expansion of the infarct at any time point and required a log concentration lower to establish a no effect level. The expansion of the I/R injury remained significantly elevated at 28 days following aspiration of the COOH and N-doped forms, but not the C-grade as compared to SS. CONCLUSION: Our results suggest that oropharyngeal aspiration of MWCNT promotes increased susceptibility of cardiac tissue to ischemia/reperfusion injury without a significant pulmonary inflammatory response. The cardiac injury effects were observed at low concentrations of MWCNTs and presence of MWCNTs may pose a significant risk to the cardiovascular system.

Novel murine model of chronic granulomatous lung inflammation elicited by carbon nanotubes.

Lung granulomas are associated with numerous conditions, including inflammatory disorders, exposure to environmental pollutants, and infection. Osteopontin is a chemotactic cytokine produced by macrophages, and is implicated in extracellular matrix remodeling. Furthermore, osteopontin is up-regulated in granulomatous disease, and osteopontin null mice exhibit reduced granuloma formation. Animal models currently used to investigate chronic lung granulomatous inflammation bear a pathological resemblance, but lack the chronic nature of human granulomatous disease. Carbon nanoparticles are generated as byproducts of combustion. Interestingly, experimental exposures to carbon nanoparticles induce pulmonary granuloma-like lesions. However, the recruited cellular populations and extracellular matrix gene expression profiles within these lesions have not been explored. Because of the rapid resolution of granulomas in current animal models, the mechanisms responsible for persistence have been elusive. To overcome the limitations of previous models, we investigated whether a model using multiwall carbon nanoparticles would resemble chronic human lung granulomatous inflammation. We hypothesized that pulmonary exposure to multiwall carbon nanoparticles would induce granulomas, elicit a macrophage and T-cell response, and mimic other granulomatous disorders with an up-regulation of osteopontin. This model demonstrates: (1) granulomatous inflammation, with macrophage and T-cell infiltration; (2) resemblance to the chronicity of human granulomas, with persistence up to 90 days; and (3) a marked elevation of osteopontin, metalloproteinases, and cell adhesion molecules in granulomatous foci isolated by laser-capture microdissection and in alveolar macrophages from bronchoalveolar lavage. The establishment of such a model provides an important platform for mechanistic studies on the persistence of granuloma.

Catalytic reduction of 4-nitrophenol using biogenic gold and silver nanoparticles derived from Breynia rhamnoides.

A simple, green method is described for the synthesis of Gold (Au) and Silver (Ag) nanoparticles (NPs) from the stem extract of Breynia rhamnoides. Unlike other biological methods for NP synthesis, the uniqueness of our method lies in its fast synthesis rates (~7 min for AuNPs) and the ability to tune the nanoparticle size (and subsequently their catalytic activity) via the extract concentration used in the experiment. The phenolic glycosides and reducing sugars present in the extract are largely responsible for the rapid reduction rates of Au(3+) ions to AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs (or AgNPs) and NaBH(4) was observed and was found to depend upon the nanoparticle size or the stem extract concentration used for synthesis.

Evidence for surface states in pristine and Co-doped ZnO nanostructures: magnetization and nonlinear optical studies.

An unexpected presence of ferromagnetic (FM) ordering in nanostructured ZnO has been reported previously. Recently, from our detailed magnetization studies and ab initio calculations, we attributed this FM ordering in nanostructured ZnO to the presence of surface states, and a direct correlation between the magnetic properties and crystallinity of ZnO was observed. In this study, through a systematic sample preparation of both pristine and Co-doped ZnO nanostructures, and detailed magnetization and nonlinear optical (NLO) measurements, we confirm that the observed FM ordering is due to the presence of surface states.

Multi-walled carbon nanotube instillation impairs pulmonary function in C57BL/6 mice.

BACKGROUND: Multi-walled carbon nanotubes (MWCNTs) are widely used in many disciplines due to their unique physical and chemical properties. Therefore, some concerns about the possible human health and environmental impacts of manufactured MWCNTs are rising. We hypothesized that instillation of MWCNTs impairs pulmonary function in C57BL/6 mice due to development of lung inflammation and fibrosis. METHODS: MWCNTs were administered to C57BL/6 mice by oropharyngeal aspiration (1, 2, and 4 mg/kg) and we assessed lung inflammation and fibrosis by inflammatory cell infiltration, collagen content, and histological assessment. Pulmonary function was assessed using a FlexiVent system and levels of Ccl3, Ccl11, Mmp13 and IL-33 were measured by RT-PCR and ELISA. RESULTS: Mice administered MWCNTs exhibited increased inflammatory cell infiltration, collagen deposition and granuloma formation in lung tissue, which correlated with impaired pulmonary function as assessed by increased resistance, tissue damping, and decreased lung compliance. Pulmonary exposure to MWCNTs induced an inflammatory signature marked by cytokine (IL-33), chemokine (Ccl3 and Ccl11), and protease production (Mmp13) that promoted the inflammatory and fibrotic changes observed within the lung. CONCLUSIONS: These results further highlight the potential adverse health effects that may occur following MWCNT exposure and therefore we suggest these materials may pose a significant risk leading to impaired lung function following environmental and occupational exposures.

Selective synthesis of subnanometer diameter semiconducting single-walled carbon nanotubes.

Subnanometer single-walled carbon nanotubes (sub-nm SWNTs) were synthesized at different temperatures (600, 700, and 800 degrees C) using CoMn bimetallic catalysts supported on MCM-41 silica templates. The state of the catalyst was investigated using X-ray absorption, and the (n,m) indices of the sub-nm SWNTs were determined from Raman spectroscopy and photoluminescence measurements. We find that the size of the metallic particles that seed the growth of sub-nm SWNTs (diameter approximately 0.5-1.0 nm) is highly sensitive to the reaction temperature. Low reaction temperature (600 degrees C) favors the growth of semiconducting tubes whose diameters range from 0.5 to 0.7 nm. These results were also confirmed by electrical transport measurements. Interestingly, dominant intermediate frequency modes on the same intensity scale as the Raman breathing modes were observed. An unusual "S-like" dispersion of the G-band was present in the Raman spectra of sub-nm SWNTs with diameters <0.7 nm.

Binary III-V semiconductor core optical fiber.

For the first time to the best of our knowledge a glass-clad optical fiber comprising a crystalline binary III-V semiconductor core has been fabricated. More specifically, a phosphate glass-clad fiber containing an indium antimonide (InSb) core was drawn using a molten core approach. The core was found to be highly crystalline with some oxygen and phosphorus diffusing in from the cladding glass. While optical transmission measurements were unable to be made, most likely due to free carrier absorption associated with the conductivity of the core, this work constitutes a proof-of-concept that optical fibers comprising semiconductor cores of higher crystallographic complexity than previously realized can be drawn using conventional fiber fabrication techniques. Such binary semiconductors may open the door to future fiber-based nonlinear devices.

Rapid detection of urokinase plasminogen activator using flexible paper-based graphene-gold platform.

Many studies have shown that urokinase plasminogen activator (uPA) is causally involved in promoting cancer invasion and metastasis. Thus, monitoring uPA levels could be very useful in cancer diagnosis, identification of initial metastasis, and guiding cancer treatment. Here, the authors developed a novel and scalable uPA sensor based on a graphene-gold nanoparticle platform that uses fluorescence of quantum dots to rapidly (<1 h) detect uPA up to 100 pM. Indeed, the authors' sensor is highly selective and showed an ability to sense up to 100 pM uPA even in the presence of complex biological milieu such as the fetal bovine serum.