A novel nanomaterial/ionophore-modified glassy carbon electrode for anodic stripping analysis of lead (Pb 2+ ) is described. Nanosized hydroxyapatite (NHAP) with width of 20-25 nm and length of 50-100 nm has been prepared and used to improve the sensitivity for detection of Pb 2+ because it provides unique threedimensional network structure and has strong adsorption ability toward Pb 2+ . An ionophore, usually used in ion-selective electrodes, is utilized here for its excellent selectivity toward Pb 2+ . Nafion, a cationexchange polymer, is employed as the conductive matrix in which NHAP and the ionophore can be tightly attached to the electrode surface. Such a designed NHAP/ionophore/Nafion-modified electrode shows remarkably improved sensitivity and selectivity to Pb 2+ . The electrode has a linear range of 5.0 nM to 0.8 µM with a 10 min accumulation time at open-circuit potential. The sensitivity and detection limit of the proposed sensor are 13 µA/µM and 1.0 nM, respectively. Interference from other heavy metal ions such as Cd 2+ , Cu 2+ , and Hg 2+ associated with lead analysis can be effectively diminished. The practical application of the proposed sensor has been carried out for determination of trace levels of Pb 2+ in real water samples.

A new catalyst support, polyoxometalate-modified carbon nanotubes, is presented in this paper through the chemisorption between polyoxometalate and carbon. Pt and Pt-Ru nanoparticles were electrochemically deposited on polyoxometalate-modified carbon nanotubes electrodes, and their electrocatalytic properties for methanol electro-oxidation are investigated in detail. Due to the unique electrical properties of carbon nanotubes and the excellent redox properties and the high protonic conductivity of polyoxometalate, for the similar deposition charge of Pt and Pt-Ru catalysts, 1.4 times larger exchange current density, 1.5 times higher specific activity, and better cycle stabilities can be obtained at polyoxometalate-modified carbon nanotube electrodes as compared to the electrodes without polyoxometalate modification. These results show that polyoxometalate-modified carbon nanotubes as a new catalyst support have good potential application in direct methanol fuel cells.

An amperometric glucose biosensor is developed that is based on immobilization of glucose oxidase (GOD) in a composite film of poly(o-aminophenol) (POAP) and carbon nanotubes (CNT), which are electrochemically copolymerized at a gold (Au) electrode. Because of the high surface per volume ratio and excellent electrical conductivity of CNT, the biosensor based on an Au/POAP/CNT/GOD electrode has lower detection limit (0.01 mM), larger maximum response current (0.24 mA cm -2 ) and higher sensitivity (11.4 mA M -1 cm -2 ) than the values of the biosensor based on an Au/POAP/GOD electrode. Additionally, the biosensor shows fast response time, large response current, and good antiinterferent ability for ascorbic acid, uric acid and acetaminophen. Good reproducibility and stability of the biosensor are also observed.

No abstract

A simple colorimetric method with high sensitivity and selectivity was developed for sensing of nitrite as low as 4.0 mM by naked eyes, which is based on etching of gold nanorods accompanied by shape changes in aspect ratios (length/width) and a visible color change from bluish green to red and then to colorless with the increase of nitrite.As type A inorganic contaminants in drinking water, nitrite and nitrate have proven to be of great threat to human health and may result in diseases like methemoglobinemia, esophageal cancer, etc. 1-3Many methods, such as ion chromatography, 4 capillary electrophoresis, 5 chemiluminescence 6 and fluorescence spectrum, 7 have been developed for the detection of NO 2 À and NO 3 À . However, all these methods have poor applicability to field tests. As the largest developing country, China is encountering a great drinking water crisis resulting from the worsening quality of source water. The situation is even worse in its rural regions where people mainly rely on simply prepared tap water or even untreated surface water, shallow groundwater, cellar water, etc. The concentrations of NO 2 À and NO 3 À in most of such water may have reached dangerous level [8][9][10] and have barely been monitored due to the lack of funds, equipments and qualified persons. It is urgent to develop a simple test method that can be quickly handled by local inhabitants. Colorimetric assays have proven to be effective for the inspection of NO 2 À in food and wastewater. [11][12][13] It is unfortunate that photoabsorption coefficients of employed organic dyes are rather low, which withhold further applications of most colorimetric assays in the quality assurance of drinking water. Benefiting from high photoabsorption coefficients, nano-materials have been widely applied in colorimetric assays for the detection of various targets, As shown in Scheme 1, the solution of GNRs (length/diameter ratio about 1.3 : 1) appeared bluish green owing to the intense longitudinal surface plasmon resonance (SPR) absorption of GNRs around 630 nm. The addition of 10 mM NO 2 À to the colloidal solution caused a color change from bluish green to red within 20 minutes. More NO 2 À (40 mM) caused the solution to be almost colorless. The progressive color change corresponds to the partial to complete dissolution of GNRs.To confirm the dissolution of GNRs caused by NO 2 À , the absorption spectra of GNRs after incubation in NO 2 À solutions (pH z 0) at different intervals were examined. As shown in Fig. 1, the absorption spectrum of GNRs (curve a) exhibited strong SPR absorption at bands of 530 and 630 nm corresponding to the

ions trigger a Fenton-like reaction, resulting in the generation of superoxide radical (O 2 •−). As a result, the gold nanorods are gradually etched by O 2•− in the presence of SCN − , accompanied by an obvious color change from green to red. The gold nanorods etching process preferentially occurs along the longitudinal direction, which is observed by transmission electron microscope. The etching mechanism is carefully proved by investigating the effects of different radical scavengers (e.g., dimethyl sulfoxide). The auto-oxidation of hydroxylamine assay further confirms the mechanism. Then, the main factors, including reactants concentrations, temperature, and incubation time, are specifically investigated. Under optimized conditions, we get an excellent sensing performance for Co 2+ with a lower detection limit of 1.0 nM via a spectrophotometer and a visual detection limit of 40 nM. In addition, this principle may provide a new concept of "intermediate-mediated etching of nanoparticles" for sensing.

No abstract

No abstract