Metal decorated graphene materials are highly important for catalysis. In this work, noble metal doped-graphene hybrids were prepared by a simple and scalable method. The thermal reductions of metal doped-graphite oxide precursors were carried out in nitrogen and hydrogen atmospheres and the effects of these atmospheres as well as the metal components on the characteristics and catalytic capabilities of the hybrid materials were studied. The hybrids exfoliated in nitrogen atmosphere contained a higher amount of oxygen-containing groups and lower density of defects on their surfaces than hybrids exfoliated in hydrogen atmosphere. The metals significantly affected the electrochemical behavior and catalysis of compounds that are important in energy production and storage and in electrochemical sensing. Research in the field of energy storage and production, electrochemical sensing and biosensing as well as biomedical devices can take advantage of the properties and catalytic capabilities of the metal doped graphene hybrids.

The direct detection of metal nanoparticles is of high importance. Here we investigate inherent electrochemistry of silver nanoparticles of sizes 10, 40, 80 and 107 nm by means of cyclic voltammetry.Keywords: Silver nanoparticles, Size dependant electrochemical behavior DOI: 10.1002/elan.201100690 There is a high demand for facile direct detection of metallic nanoparticles (NPs) arising from various areas such as biosensing [1][2][3], water quality assessment [4] or toxicity studies [5,6]. Electrochemistry is a facile method for direct determination of a wide range of metal nanoparticles, for example gold [7,8], platinum [9], silver [10][11][12] or molybdenum [13]. The detailed investigation whether different sizes of the metal nanoparticles exhibit different electrochemical properties were carried out frequently, predominantly for Au, Pt and Ag nanoparticles. The electrochemical detection of metal nanoparticles can be carried in two formats: immobilizing the nanoparticles on the electrode surfaces [7,8,12,13] or direct detection of nanoparticles hitting the surface of the electrode [10,11]. Here we investigate the electrochemical behavior of silver nanoparticles of sizes 10-107 nm, following our previous study of size dependant response of Au NPs (2-50 nm) [8] and also Comptons previous study of size dependency of voltammetry of Ag NPs [14][15][16][17][18]. Comptons group demonstrated theoretically and experimentally that stripping potential of Ag NPs depends on the size of the particles [14]. We confine ourselves to the traditional method of immobilization of particular sized nanoparticles on the surface of the electrodes. We also purposely did not used electrochemically generated Ag NPs [19] as such generation of NPs leads to wide size distribution but rather commercially available Ag NPs with narrow size distribution.We studied the influence of the size of the silver nanoparticles upon their electrochemical behavior in 50 mM phosphate buffer (pH 7.4) using cyclic voltammetry. There is apparent feature of electrochemical dissolution (stripping) of silver nanoparticles on the electrode surface, at~+ 440 mV and reduction of the generated silver ions in the oxidative part of cycle from the solution at+ 100 mV. As it can be seen from the voltammograms, the behavior of various silver nanoparticles significantly differs, depending on the size of the nanoparticles. First observation one can make is that 10 and 40 nm Ag NPs exhibit two oxidative peaks, denoted as Ox 1 and Ox 2. While Ox 2 peak potential is cycle number independent and it is practically identical for both 10 and 40 nm Ag NPs (of 443 mV for 10 nm Ag NPs; and of 445 mV for 40 nm Ag NPs), the potential of the first oxidation peak (Ox 1) changes with consecutive scans, reflecting the fact that every cycle there is the reduction of the electrogenerated Ag + ions which results into the nucleation of silver nanostructures at GC and Ag NPs surfaces (note that during oxidation step not all silver is dissolved). Figure 2 shows that potential Ox 1 decr...

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In addition to being a repository of genetic information, DNA is a bio-polymer that can be formed into various nanostructures. This profound ability to engineer various moieties has expanded its role from data storage to a structural biomaterial for sensing applications. In this study, we anchored DNA nano-pyramids (DPs) to gold electrodes for the electrochemical sensing of immunoglobulin G (IgG), an important antibody produced in response to infection. The pyramidal DNA structure not only avoids entanglement with neighboring probes through the use of spatially separating pendant probes but also reduces the local overcrowding effect with the overall enhanced packing of targets. The results from electrochemical impedance spectroscopy measurements also show that DP layer has better conductivity, with the hollow structure further facilitating electron transfer and increasing the sensitivity of electrochemical detection. We are able to selectively detect IgG in the presence of other proteins in an analyte solution. The limit of detection was 2.8 pg ml À1 . Our ferrocene-labeled sandwich immunoassay works at 37 1C under a neutral pH environment. It also produces stable and reproducible signals even after storage for 1 week at 4 1C, further demonstrating the potential of this sensing system for clinical applications.

Engineered nanoparticles (ENPs) are increasingly detected in water supply due to environmental release of ENPs as the by-products contained within the effluent of domestic and industrial run-off. The partial recycling of water laden with ENPs, albeit at ultra-low concentrations, may pose an uncharacterized threat to human health. In this study, we investigated the toxicity of three prevalent ENPs: zinc oxide, silver, and titanium dioxide over a wide range of concentrations that encompasses drinking water-relevant concentrations, to cellular systems representing oral and gastrointestinal tissues. Based on published in silico-predicted water-relevant ENPs concentration range from 100 pg/L to 100 µg/L, we detected no cytotoxicity to all the cellular systems. Significant cytotoxicity due to the NPs set in around 100 mg/L with decreasing extent of toxicity from zinc oxide to silver to titanium dioxide NPs. We also found that noncytotoxic zinc oxide NPs level of 10 mg/L could elevate the intracellular oxidative stress. The threshold concentrations of NPs that induced cytotoxic effect are at least two to five orders of magnitude higher than the permissible concentrations of the respective metals and metal oxides in drinking water. Based on these findings, the current estimated levels of NPs in potable water pose little cytotoxic threat to the human oral and gastrointestinal systems within our experimental boundaries.