An Acetylcholinesterase Biosensor Based on Graphene/ Polyaniline Composite Film for Detection of Pesticides

This work reports a sensitive amperometric biosensor for organophosphate pesticides （OPs） fabricated through modifying glassy carbon electrode with acetylcholinesterase （ACHE） immobilized on graphene/polyaniline （G/PANI） composite film. The obtained G/PANI composite films show large specific area, high conductivity, good biocompatibility, and fast redox properties and have perfect layered and encapsulated structures. The as-prepared biosensor shows high affinity to acetylthiocholine （ATC1） with a Micbaelis-Menten constant value of 0.20 mmol/L. Furthermore, based on the inhibition of the enzymatic activity （immobilized ACHE） caused by the model compound of carbaryl （one kind of pesticides）, it is found that the inhibition activity of carbaryl is proportional to its concen- tration ranging from 38 to 194 ngomL-1. The developed biosensor shows a detection limit of 20 ngomL-1 （S/N~ 3） for OPs detection and exhibits good performance such as good reproducibility and acceptable stability, which makes it possible to provide a new and promising tool for the analysis of enzyme inhibitors.

Facile Synthesis of Pd-Ni Nanoparticles on Reduced Graphene Oxide under Microwave Irradiation for Formic Acid Oxidation

Pd and PdxNi nanoparticles have been supported on reduced graphene oxide （Pd/rGO and PdxNi/rGO） by using the microwave-assisted heating method in glycol. The morphology, composition and electrochemical performance have been characterized by TEM, XRD, XPS and electrochemical methods. The XRD and XPS results show that there are no PdNi alloy particles formed in PdxNi/rGO and the composites exist mostly in the form of Pd^0 and NiOOH species. The electrochemical results reveal that PdxNi/rGO synthesized from the feeding source of Pd and Ni with an atomic ratio of 4 ： 1 exhibits higher activity, better stability and smaller electron transfer resistance to- ward formic acid electro-oxidation compared with commercial Pd/C, Pd/rGO and other PdxNi/rGO samples. The excellent electrocatalytic performance indicates that the addition of appropriate amount of Ni can greatly enhance the activity and stability of Pd catalysts for formic acid oxidation.

Capacitive Performances of Reduced Graphene Oxide Hydrogel Prepared by Using Sodium Hypophosphite as Reducer

The hydrogels of reduced graphene oxide （rGOHGs） have been synthesized through treating GO with various concentrations of sodium hypophosphite （NaH2PO2） under hydrothermal condition. The results reveal that the structure of rGOHGs changes along with the increase of the concentration of NaH2PO2. The rGO sheets prepared with low concentration of NaH2PO2 exhibit more crimples and larger specific surface area than those prepared with high concentration of NaH2PO2. The measurements of the capacitive performances of rGOHGs reveal that the rGOHGs prepared with low concentration of NaH2PO2 possess larger specific capacitance （Cs） than that prepared with high concentration of NaH2PO2 at low cyclic voltammetry scan rates. However, the rGOHGs prepared with high concentration of NaH2PO2 possess larger Cs at high scan rates, more stability and better high-rate capability than those prepared at low concentration. It is believed that the structures and properties of rGOHGs can be adjusted by controlling the concentration of NaH2PO2 according to the requirement.

Sulfonated Graphene Synthesized via a Green Route and Its Capacitive Properties

An environmentally friendly approach is presented to synthesize sulfonated reduced graphene oxide （S-rGO） by using L-ascorbic acid （L-AA） and aryl diazonium salt of sulfanilic acid. The preparation conditions have been optimized in order to obtain isolated and conductive S-rGO, and the products have been characterized by Ultraviolet-Visible spectroscopy, Fourier transformed infrared spectroscopy, Raman, X-ray photoelectron spectroscopy and X-ray powder diffraction and electrochemical methods. The results show that the S-rGO sheets possess excellent water-solubility and high electrical conductivity, which implies that the oxygen-containing functional groups have been removed and conjugated sp2 network has been restored. What＇s more, the electrochemical measurements reveal that the capacitive performance of the S-rGO has been improved compared with the graphene oxide （GO） and the reduced graphene oxide （rGO, reduced by L-AA）. The optimum S-rGO exhibits a specific capacitance of 205 F·g^-1 and good cycling stability （3.9% decreasing after 10000 cycles）, which are better than those for graphene oxide （109 F·g^-1 and decreasing 6.6% after 10000 cycles） and rGO （139 F·g^-1 and decreasing ll.3% after 10000 cycling）. This approach proves a new route to improve the capacitive properties of rGO.