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We report on a pair of highly sensitive amperometric biosensors for organophosphate pesticides (OPs) based on assembling acetylcholinesterase (AChE) on poly(dimethylsiloxane) (PDMS)-poly(diallydimethylemmonium) (PDDA)/gold nanoparticles (AuNPs) composite film. Two AChE immobilization strategies are proposed based on the composite film with hydrophobic and hydrophilic surface tailored by oxygen plasma. The twin biosensors show interesting different electrochemical performances. The hydrophobic surface based PDMS-PDDAN AuNPs/choline oxidase (ChO)/AChE biosensor (biosensor-1) shows excellent stability and unique selectivity to hypertoxic organophosphate. At optimal conditions, this biosensor-1 could measure 5.0 x 10(-10) g/L paraoxon and 1.0 x 10(-9) g/L parathion. As for the hydrophilic surface based biosensor (biosensor-2), it shows no selectivity but can be commonly used for the detection of most OPs. Based on the structure of AChE, it is assumed that via the hydrophobic interaction between enzyme molecules and hydrophobic surface, the enzyme active sites surrounded by hydrophobic amino acids face toward the surface and get better protection from OPs. This assumption may explain the different performances of the twin biosensors and especially the unique selectivity of biosensor-1 to hypertoxic OPs. Real sample detection was performed and the omethoate residue on Cottomrose Hibiscus leaves was detected with biosensor-1.

We report a simple method of catalytic deposition of Pb on a gold nanofilm substrate, which was in situ prepared and used as nanocrystal seeds. Due to the unique properties of gold nanocrystal seeds, Pb could be catalytically deposited on the surface of the gold nanofilm. Compared with the deposition of Pb on bare gold electrode, a larger amount of Pb was deposited on the gold nanofilm and the electrical response was amplified significantly. The catalytic deposition of Pb on the gold nanofilm was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. A stable and quasi-reversible redox couple was obtained in neutral solution and studied in detail. The surface of the gold nanofilm could be easily regenerated in 0.1 mol L(-1) nitric acid solution. Since the redox peaks of Pb could be effectively separated from those of other metals such as Cu, Cd, and Zn, a selective determination of Pb2+ was achieved. Linear sweep voltammetry (LSV) was used for the determination of Pb2+. The peak currents of Pb varies linearly with the concentration of Pb2+ in aqueous solution ranging from 1.0 to 10.0 micromol L(-1) (R=0.999), with a detection limit of 0.1 micromol L(-1). It is expected that the gold nanofilm will facilitate the appearance of heavy metal ion sensors with good performance.