Yuqing Miao

Water soluble poly (vinyl alcohol) (PVA) was used to prepare the enzyme membranes of acetylcholinesterase (AChE) for electrochemical assaying methyl parathion in water insoluble organic solvent. The immobilized enzyme was separated from electrode for the development of enzyme inhibition-based bioassays. This assay is simple and convenient where enzyme membrane is applicable for single use and the electrode for repeated use. The enzyme membranes can be used handily piece by piece and the released AChE performs catalytic reaction homogeneously. The inhibition percentage of AChE increases with the concentration of methyl parathion ranging from 0.1 to 1 mg/mL.

A novel technique of enzyme immobilization is developed for making the immobilized enzymes capable of further releasing for homogeneous reaction. Water-soluble poly(vinyl alcohol) was used to prepare enzyme-loaded membranes with immobilized acetylcholinesterase (AChE). When used, a piece of enzymecontaining membrane is put into the solution and dissolves quickly. The released AChE is mixed and interacts with substrates and carbaryl inhibitors. The catalytical activity and inhibition sensitivity of released enzyme are comparable to those of free AChE. The values of Michaelis constant and maximum reaction rate for released AChE are also very close to those for free AChE. The experimental conditions such as the concentrations of PVA and acetone, the time of enzymatic reaction and that of AChE inhibition by carbaryl pesticide were optimized. The relative inhibition of AChE activity increased with the carbaryl concentration ranging from 0.1 μg/L to 100 mg/L. When compared to free AChE in solution or solid powder, the prepared PVA-AChE membranes are advantageous with respect to storage and handling. The suggested technique of enzyme immobilization is suitable for the variety of applications, when the enzyme catalysed reactions allows for single-using of the active material and does not require further enzyme recovering.

We report on the characterization, assembly and electroanalytical performance of Prussian blue/polypyrrole (PBPPy) composite nanoparticles synthesized by the reverse micelle method. Scanning electron microscopy suggests the formation of nanosized PBPPy particles with diameters between 40 and 50 nm. Optical absorption confirms that the particles are composed of Prussian blue (PB) and polypyrrole. PB and PBPPy nanoparticles were anchored onto the surface of cysteine-modified Au electrodes. Cyclic voltammetry experiments show that PB- or PBPPy-modified electrodes exhibit intrinsic electrochemical properties and a high electrocatalytic activity towards H2O2. PBPPy-modified electrodes exhibit a higher sensitivity to H2O2 than PB-modified electrodes. A linear calibration curve in the concentration range 0.99 μM–8.26 mM H2O2 is constructed with a detection limit of 0.23 μM at a signal-to-noise ratio of 3. Excellent stability is observed for PBPPy-composite-nanoparticle-modified electrodes even in a pH 6 ...

Magnified image Hemin could be dissolved directly in H₂O solution in the presence of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB). The hemin is adsorbed on the surface of single‐wall‐carbon‐nanotube‐modified glassy carbon (GC) electrodes by self‐assembly. The modified electrodes exhibit a well‐defined, reversible redox peak with the reduction potential at −0.30 V and a potential separation of 61 mV at pH 7.0. The peak current is found to increase linearly with the scan rate in the range 25–200 mV, and the peak potential is pH‐dependent. The modified electrodes exhibit obvious signal enhancement for the electrochemical reduction of O₂ and H₂O₂, and oxidation of L‐cysteine, which is useful to develop their application in electroanalysis and biosensors.