Promoting Cell Proliferation Using Water Dispersible Germanium Nanowires

Group IV Nanowires have strong potential for several biomedical applications. However, to date their use remains limited because many are synthesised using heavy metal seeds and functionalised using organic ligands to make the materials water dispersible. This can result in unpredicted toxic side effects for mammalian cells cultured on the wires. Here, we describe an approach to make seedless and ligand free Germanium nanowires water dispersible using glutamic acid, a natural occurring amino acid that alleviates the environmental and health hazards associated with traditional functionalisation materials. We analysed the treated material extensively using Transmission electron microscopy (TEM), High resolution-TEM, and scanning electron microscope (SEM). Using a series of state of the art biochemical and morphological assays, together with a series of complimentary and synergistic cellular and molecular approaches, we show that the water dispersible germanium nanowires are non-toxic and are biocompatible. We monitored the behaviour of the cells growing on the treated germanium nanowires using a real time impedance based platform (xCELLigence) which revealed that the treated germanium nanowires promote cell adhesion and cell proliferation which we believe is as a result of the presence of an etched surface giving rise to a collagen like structure and an oxide layer. Furthermore this study is the first to evaluate the associated effect of Germanium nanowires on mammalian cells. Our studies highlight the potential use of water dispersible Germanium Nanowires in biological platforms that encourage anchorage-dependent cell growth.     

Biological synthesis of gold nanowires using extract of Rhodopseudomonas capsulata

An environmentally friendly method using a cell-free extract (CFE) of Rhodopseudomonas capsulata is proposed to synthesize gold nanowires with a network structure. This procedure offers control over the shapes of gold nanoparticles with the change of HAuCl4 concentration. The CFE solutions were added with different concentrations of HAuCl4, resulting in the bioreduction of gold ions and biosynthesis of morphologies of gold nanostructures. It is probable that proteins acted as the major biomolecules involved in the bioreduction and synthesis of gold nanoparticles. At a lower concentration of gold ions, exclusively spherical gold nanoparticles with sizes ranging from 10 to 20 nm were produced, whereas gold nanowires with a network structure formed at the higher concentration of gold ions in the aqueous solution. This method is expected to be applicable to the synthesis of other metallic nanowires such as silver and platinum, and even other anisotropic metal nanostructures are expected using the biosynthetic methods.     

Life cycle assessment of emerging technologies at the lab scale: The case of nanowire‐based solar cells

Nanomaterials are expected to play an important role in the development of sustainable products. The use of nanomaterials in solar cells has the potential to increase their conversion efficiency. In this study, we performed a life cycle assessment (LCA) for an emerging nanowire‐based solar technology. Two lab‐scale manufacturing routes for the production of nanowire‐based solar cells have been compared—the direct growth of GaInP nanowires on silicon substrate and the growth of InP nanowires on native substrate, peel off, and transfer to silicon substrate. The analysis revealed critical raw materials and processes of the current lab‐scale manufacturing routes such as the use of trifluoromethane (CHF₃), gold, and an InP wafer and a stamp, which are used and discarded. The environmental performance of the two production routes under different scenarios has been assessed. The scenarios include the use of an alternative process to reduce the gold requirements—electroplating instead of metallization, recovery of gold, and reuse of the InP wafer and the stamp. A number of suggestions, based on the LCA results—including minimization of the use of gold and further exploration for upscaling of the electroplating process, the increase in the lifetimes of the wafer and the stamp, and the use of fluorine‐free etching materials—have been communicated to the researchers in order to improve the environmental performance of the technology. Finally, the usefulness and limitations of lab‐scale LCA as a tool to guide the sustainable development of emerging technologies are discussed.     

Ultrasensitive detection of cortisol with enzyme fragment complementation technology using functionalized nanowire

Cortisol is a member of the glucocorticoid hormone family and a key metabolic regulator. Increased intracellular cortisol levels have been implicated in type 2 diabetes, obesity, and metabolic syndrome. Cortisol is an important bio-marker of stress and its detection is also important in sports medicine. However, rapid methods for sensitive detection of cortisol are limited. Functionalized gold nanowires were used to enhance the sensitivity and selectivity of cortisol detection. Gold nanowires are used to improve the electron transfer between the electrodes. Moreover, the large surface to volume ratio, small diffusion time and high electrical conductivity and their aligned nature will enhance the sensitivity and detection limit of the biosensor several fold. The biosensor was fabricated using, aligned gold (Au) nanowires to behave as the working electrode, platinum deposited on a silicon chip to function as the counter electrode, and silver/silver chloride as reference electrode. The gold nanowires were coupled with cortisol antibodies using covalent linkage chemistry and a fixed amount of 3alpha-hydroxysteroid dehydrogenase was introduced into the reaction cell during each measurement to convert (reduce) ketosteroid into hydroxyl steroid. Furthermore, the micro-fluidic, micro-fluid part of the sensor was fabricated using micro-electro-mechanical system (MEMS) technology to have better control on liquid flow over Au nanowires to minimize the signal to noise ratio. The biosensor was characterized using SEM, AFM and FTIR technique. The response curve of the biosensor was found to be linear in the range of 10-80 microM of cortisol. Moreover, the presence of hydrocortisone is sensitively detected in the range of 5-30 microM. It is concluded that the functionalized gold nanowires with micro-fluidic device using enzyme fragment complementation technology can provide an easy and sensitive assay for cortisol detection in serum and other biological fluids.     

Multishelled Gold Nanowires

Abstract

The current miniaturization of electronic devices raises many questions about the properties of various materials at nanometre-scales. Recent molecular dynamics computer simulations have shown that small finite nanowires of gold exist as multishelled structures of lasting stability. These classical simulations are based on a well-tested embedded atom potential. Molecular dynamics simulation studies of metallic nanowires should help in developing methods for their fabrication, such as electron-beam litography and scanning tunneling microscopy.     

Intrinsically Stretchable Fuel Cell Based on Enokitake‐Like Standing Gold Nanowires

Conventional fuel cells are based on rigid electrodes, limiting their applications in wearable and implantable electronics. Here, it is demonstrated that enokitake‐like vertically‐aligned standing gold nanowires (v‐AuNWs) can also serve as powerful platform for stretchable fuel cells by using ethanol as model system. Unlike traditional fuel cell electrodes, the v‐AuNWs have “Janus Morphology” on both sides of the film and also are highly stretchable. The comparative studies demonstrate that tail side exposed v‐AuNWs based stretchable electrodes outperform the head‐side exposed v‐AuNWs toward the electro‐oxidation of ethanol due to the direct exposure of high‐surface‐area nanowires to the fuels. Therefore, a stretchable fuel cell is fabricated utilizing tail side based interdigitated electrodes, where v‐AuNWs and Pt black modified v‐AuNWs serve as the anode and cathode, respectively. The as‐prepared stretchable fuel cell exhibits good overall performance, including high power density, current density, open‐circuit voltage, stretchability, and durability. Most importantly, a wearable fuel cell is also achieved by integrating tattoo‐like interdigitated electrodes with a thin layer of sponge as a fuel container, exhibiting good performance under various deformations (compression, stretching, and twisting). Such attractive performance in conjunction with skin‐like in‐plane design indicates its great potential to power the next‐generation of wearable and implantable devices.     

High Performance Flexible Supercapacitor Electrodes Composed of Ultralarge Graphene Sheets and Vanadium Dioxide

Little is known regarding the effect of the graphene lateral size on the electrochemical performance of hybrid graphene electrode. This work examines the electrochemical performance of a flexible hybrid supercapacitor electrode composed of ultralarge graphene oxide (UGO; mean lateral size of 47 ± 22 μm) and vanadium dioxide (VO₂) nanobelts, referring to a reference electrode composed of small scale graphene oxide (SGO; mean lateral size of 0.8 ± 0.5 μm) and VO₂.Thermal treatment converts UGO/VO₂ and SGO/VO₂ to URGO/VO₂ (denoted VURGO) and SRGO/VO₂ (denoted VSRGO) electrodes, respectively. The sheet resistance of the VURGO film (0.57 ± 0.03 kΩ sq.^–1) was two orders of magnitude lower than that of the VSRGO (55.74 ± 9.35 kΩ sq.^–1). The VURGO hybrid electrode showed a specific capacitance of 769 F g^?1, which was significantly better than the corresponding values for the VSRGO electrode (385 F/g). These results support the notion that the use of ultralarge graphene sheets (≈22 500 μm²) lowers the intersheet resistance due to the presence of fewer intersheet tunneling barriers. This article highlights the potential utility of URGO (as a conductive support) in hybrid electrode containing VO₂ nanobelts for high performance flexible hybrid supercapacitor.     

Functionalization of magnetic nanowires by charged biopolymers

We report on a facile method for the preparation of biocompatible and bioactive magnetic nanowires. The method consists of the direct deposition of polysaccharides by layer-by-layer (LbL) assembly onto a brush of metallic nanowires obtained by electrodeposition of the metal within the nanopores of an alumina template supported on a silicon wafer. Carboxymethylpullulan (CMP) and chitosan (CHI) multilayers were grown on brushes of Ni nanowires; subsequent grafting of an enzyme was performed by conjugating free amine side groups of chitosan with carboxylic groups of the enzyme. The nanowires are finally released by a gentle ultrasonic treatment. Transmission electron microscopy, electron energy-dispersive loss spectroscopy, and x-ray photoelectron spectroscopy indicate the formation of an homogeneous coating onto the nickel nanowires when one, two, or three CMP/CHI bilayers are deposited. This easy and efficient route to the biochemical functionalization of magnetic nanowires could find widespread use for the preparation of a broad range of nanowires with tailored surface properties.     

Design of five‐layer gold nanoparticles self‐assembled in a liquid open tubular column for ultrasensitive nano‐LC‐MS/MS proteomic analysis of 80 living cells

In this work, for the first time, a liquid open tubular column modified by five‐layer gold nanoparticles and linked with C₁₈ (GNPs@C₁₈) was designed and fabricated for nano‐LC‐MS/MS analysis of 80 living cells. Sixty nanometer gold nanoparticles were self‐assembled layer by layer on the inner wall of a 20 μm id fused‐silica capillary. C₁₈ was then linked on the gold nanoparticles to make the liquid open tubular column show hydrophobic character. Enough loading capacities for analysis of 80 living cells, ～100 fmol for pk‐10 and ～30 fmol for insulin, were obtained with the 2 m × 20 μm id five‐layer GNPs@C₁₈ open tubular column. The open tubular column was used in an online pretreatment and direct nano‐LC‐MS/MS analysis system to analyze 80 living HepG2 cells. In total, 650 proteins were identified in triplicate runs. The subcellular localization of the identified proteins showed that our system had no bias toward different cellular compartments. Protein copy number per cell of the identified proteins showed that the detection limit could reach 50 zmol and the abundance of the identified proteins could cover a dynamic range of 6 orders.     

Cultivation and processing of Linum usitatissimum and Camelina sativa in southern Scandinavia during the Roman Iron Age

Charred seed conglomerates of Linum usitatissimum (flax) and Camelina sativa (gold of pleasure) were found at Uppåkra 2:25, a Roman Iron Age site in Skåne, southern Sweden. The conglomerates showed no mixing with each other, as they were almost pure flax and gold of pleasure respectively. Together with other archaeobotanical data from the site, they provide new evidence on the use, processing and cultivation of these two plants in early Iron Age in Scandinavia. Metric analyses were applied to flax seeds from both conglomerates and other contexts at this site, and compared to seed assemblages from other Roman Iron Age sites in Europe. The comparison showed that the flax cultivation at Uppåkra 2:25 was intended for the production of oil-rich seeds. The contextual relationship indicates that both flax and gold of pleasure seeds were processed in a similar way and used for oil. Furthermore, the pure seed conglomerate of gold of pleasure suggests that this plant was not a weed, but rather an intentionally grown crop which was cultivated separately from flax.     

Gold Nanowire and Nanorod Plasmonic Mechanisms for Increasing Ultra-Thin Organic Photovoltaic Active Layer Absorption

We theoretically investigate the effect of incorporating gold cylindrical- and ellipsoidal-shaped nanowires and gold nanorods situated centrally within the active layer of organic bulk-heterojunction photovoltaic devices, on the optical absorption performance using finite element electromagnetic simulations. Gold cylindrical nanowire-embedded devices show increased active layer absorption enhancement with increasing radius; however, this effect decreases with the introduction of a polystyrene dielectric capping layer around the nanowires. Active layer absorption, with respect to changes in the orientation, aspect ratio, periodicity, and spacing between ellipsoidal nanowires were optimized. A maximum absorption enhancement weighted by AM 1.5 solar spectrum of 17 % is predicted for gold ellipsoidal nanowires of aspect ratio of 1.167 with in-plane horizontal orientation and arranged with periodicity of 35 nm within a 30-nm thin active layer. We attribute this enhancement primarily to interparticle electromagnetic coupling between adjacent nanowires, where, a maximum spatial and spectral overlap of the electromagnetic field with the absorption band of the active layer material is achieved. This effect increases with decreasing aspect ratio as well as decreasing periodicity with a trade-off observed between nanowire packing density and the active layer absorption enhancement. For gold nanorod-embedded organic photovoltaic devices, the inter-particle electromagnetic coupling effects are weaker and longitudinal surface–plasmon resonances supported by the nanorods are more pronounced. However, since the longitudinal surface–plasmon resonances occur at wavelengths greater than the absorption edge of the photovoltaic active layer, a mere 3.4 % increase in absorption enhancement is achieved for the photovoltaic device incorporating gold nanorods with aspect ratio of 1.167 and periodicity of 35 nm.     

Magnetic resonance imaging of glutamate

Glutamate, a major neurotransmitter in the brain, shows a pH- and concentration-dependent chemical exchange saturation transfer effect (GluCEST) between its amine group and bulk water, with potential for in vivo imaging by nuclear magnetic resonance. GluCEST asymmetry is observed ～3 p.p.m. downfield from bulk water. Middle cerebral artery occlusion in the rat brain resulted in an ～100% elevation of GluCEST in the ipsilateral side compared with the contralateral side, predominantly owing to pH changes. In a rat brain tumor model with blood-brain barrier disruption, intravenous glutamate injection resulted in a clear elevation of GluCEST and a similar increase in the proton magnetic resonance spectroscopy signal of glutamate. GluCEST maps from healthy human brain were also obtained. These results demonstrate the feasibility of using GluCEST for mapping relative changes in glutamate concentration, as well as pH, in vivo. Contributions from other brain metabolites to the GluCEST effect are also discussed.     

Modeling of a C‐end rule peptide adsorbed onto gold nanoparticles

The RPAR peptide, a prototype C‐end Rule (CendR) sequence that binds to neuropilin‐1 (NRP‐1), has potential therapeutic uses as internalization trigger in anticancer nanodevices. Recently, the functionalization of gold nanoparticles with CendR peptides has been proved to be a successful strategy to target the NRP‐1 receptor in prostate cancer cells. In this work, we investigate the influence of two gold surface facets, (100) and (111), on the conformational preferences of RPAR using molecular dynamics simulations. Both clustering and conformational analyses revealed that the peptide backbone becomes very rigid upon adsorption onto gold, which is a very fast and favored process, the only flexibility being attributed to the side chains of the two Arg residues. Thus, the different components of RPAR tend to adopt an elongated shape, which is characterized by the pseudo‐extended conformation of both the backbone and the Arg side chains. This conformation is very different from the already known bioactive conformation, indicating that RPAR is drastically affected by the substrate. Interestingly, the preferred conformations of the peptide adsorbed onto gold facets are not stabilized by salt bridges and/or specific intramolecular hydrogen bonds, which represent an important difference with respect to the conformations found in other environments (e.g. the peptide in solution and interacting with NRP‐1 receptor). However, the conformational changes induced by the substrate are not detrimental for the use of gold nanoparticles as appropriate vehicles for the transport and targeted delivery of the RPAR. Thus, once their high affinity for the NRP‐1 receptor induces the targeted delivery of the elongated peptide molecules from the gold nanoparticles, the lack of intramolecular interactions facilitates their evolution towards the bioactive conformation, increasing the therapeutic efficacy of the peptide.     

Nucleation and growth of microtubules from gamma-tubulin-functionalized gold surfaces

Microtubules are protein filaments that are emerging as potential building blocks in manufacturing nanoscale structures and systems such as interconnecting nanowires. Future development in using microtubules necessitates a control of their nucleation and growth. We report the controlled nucleation and growth of microtubules from functionalized gold on a hydrophilic oxidized silicon wafer. The gold substrate is functionalized with gamma-tubulin, a natural nucleating agent for microtubule growth. We show that the attached gamma-tubulin retains its biological functionality and leads to nucleation and assembly of microtubules from the functionalized gold surface. We also analyze the interplay between the geometry of the nucleating substrates and the morphology of microtubules arrays and networks grown from them. We consider two geometrical arrangements of the substrates: (a) a square lattice of small gold pads on a hydrophilic oxidized silicon wafer and (b) a large flat surface. Fluorescence microscopy and scanning electron microscopy are employed to provide a detailed characterization of the length and morphology of the nucleated and grown microtubules. The observed microtubule morphologies are modeled, analyzed and discussed within the context of reaction-diffusion and nucleation controlled processes.     

Chitosan-reduced gold nanoparticles: a novel carrier for the preparation of spray-dried liposomes for topical delivery

Exposure of skin to various chemical and physical agents results in excessive stress to the outermost cell layer of the skin, causing different degenerative effects that can be minimized by using antioxidant formulations. The major challenge, in this regard, is to develop a formulation, which can prevent photodegradation of the actives, thus allowing a significant amount to be deposited at the site. In recent decades, liposomal formulations have been extensively employed to overcome the barrier properties of the skin and photodegradation of actives. In the present study, chitosan-reduced gold nanoparticles were investigated for its potential as a carrier to prepare liposomes by a spray-drying method. Liposomes so obtained were characterized for phospholipid recovery, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, particle size, zeta potential, encapsulation efficiency, and deposition of drug and gold nanoparticles in the rat skin. Further, a liposomal gel formulation was prepared using Carbopol^® 980 NF (Noveon Systems, Kochi, India) and evaluated for drug deposition in the skin. Antioxidant activity of vitamin C encapsulated in gold liposomes was determined on a human leukemia (HL-60) cell line. The use of gold nanoparticles as a carrier showed improved phospholipid recovery and thus overcomes the liposome scalability problem. DRIFT spectra confirmed the presence of phospholipid in the formulation. Liposomal gel showed improved drug deposition, as compared to control and marketed preparations. A more interesting contribution of the chitosan-reduced gold nanoparticles was an enhanced antioxidant activity seen in case of the vitamin C–loaded gold liposomal formulation. Liposomal formulation was found to be stable for 3 months at 30°C and 65% relative humidity.     

Environmental impacts of gold mining in Essakane site of Burkina Faso

In this study, environmental impacts on air, water, and soil pollution caused by the exploit of Essakane gold mine, which is located in North Eastern part of Burkina Faso were investigated. Analyses on drinking water were made in the laboratory to determine the concentration of essential chemicals used in gold mining. Dust fallouts have been measured to assess the level of air pollution. The results showed that exploiting of gold mine directly or indirectly contributes to air pollution in Essakane district. The use of chemicals such as cyanide (industrial gold mining) and mercury (artisanal gold mining) to obtain the gold from the ore constitutes a potential risk for the ecosystem, the local population's health, and livestock production. The results also showed that there is a significant degradation of natural landscape and topography of the soil by open-pits mining (industrial mine) and holes dug by artisanal miners.     

有序样方聚类在植被垂直划分中的应用

 本文介绍一种非等级分类方法——有序样方聚类法,并将其应用于山西绵山植被垂直带的划分,结果为：1,落叶阔叶林带(包含3个亚带：Ⅰ．落叶阔叶灌丛亚带,Ⅱ．松栎林亚带,Ⅲ．落叶阔叶林亚带),2．寒温性针叶林带和3,亚高山草甸带。基于黄金分割法(或Fisher’s法)的有序样方聚类法,是按照样方在空间(或时间)先后出现的序号和组内相似性最大,组间相似性最小的标准,对样方进行分类,因此,所得结果是最优的。与TWINSPAN的结果比较,在绵山植被遭到严重扰动的情况下,有序样方聚类要优于TWINSPAN。     

Modelling of Polarization-Dependent Loss in Plasmonic Nanowire Waveguides

We have investigated the potential of using gold nanowires embedded in a dielectric cladding environment as polarization-independent long-range surface plasmon polariton waveguides at telecom wavelengths. We performed finite-element analysis on various symmetric and close-to-symmetric cross-sectional geometries and evaluated the effects of cladding thickness on the propagation and coupling loss. The calculations confirm that fabrication of polarization-independent waveguides with reasonable tolerances is feasible and that straight-waveguide insertion losses around 1.5 dB for short (0.5 mm) devices can be realized when coupling to and from conventional dielectric waveguide geometries.     

Electrochemical sensor systems based on one-dimensional (1D) nanostructures for analysis of bioaffinity interactions

Modification of screen printed graphite electrodes (SPE) with gold nanoparticles (AuNPs) decorated Pb nanowires (PbNWs) enhances such analytical characteristics of the sensor as effective surface area, electrocatalytic properties and kinetics of heterogeneous electron transfer. The reason for such improvement may be associated with the synergistic effect of AuNPs and PbNWs. Nanowires ensembles on the electrode surface were employed for the detection of cardiac myoglobin in human blood, cytochrome P450 2B4, cytochrome c. Composite materials based on nanoparticles with different dimensions (three dimensional (3D) gold nanoparticles and one dimensional (1D) Pb nanowires) create a platform for electrochemical analysis of proteins with low detection limits.     

Regime Shift in Fertilizer Commodities Indicates More Turbulence Ahead for Food Security

Recent human population increase has been enabled by a massive expansion of global agricultural production. A key component of this “Green Revolution” has been application of inorganic fertilizers to produce and maintain high crop yields. However, the long-term sustainability of these practices is unclear given the eutrophying effects of fertilizer runoff as well as the reliance of fertilizer production on finite non-renewable resources such as mined phosphate- and potassium-bearing rocks. Indeed, recent volatility in food and agricultural commodity prices, especially phosphate fertilizer, has raised concerns about emerging constraints on fertilizer production with consequences for its affordability in the developing world. We examined 30 years of monthly prices of fertilizer commodities (phosphate rock, urea, and potassium) for comparison with three food commodities (maize, wheat, and rice) and three non-agricultural commodities (gold, nickel, and petroleum). Here we show that all commodity prices, except gold, had significant change points between 2007–2009, but the fertilizer commodities, and especially phosphate rock, showed multiple symptoms of nonlinear critical transitions. In contrast to fertilizers and to rice, maize and wheat prices did not show significant signs of nonlinear dynamics. From these results we infer a recent emergence of a scarcity price in global fertilizer markets, a result signaling a new high price regime for these essential agricultural inputs. Such a regime will challenge on-going efforts to establish global food security but may also prompt fertilizer use practices and nutrient recovery strategies that reduce eutrophication.