Composite assembly of silver nanoparticles with avidin and biotinylated AChE on gold for the pesticidal electrochemical sensing

An amperometric pesticide biosensor has been devised by the composite assembly of silver nanoparticles with avidin and biotinylated acetylcholinesterase (AChE) on gold electrodes modified with a biotin-terminated self assembly monolayer (SAM). This composite assembly strategy takes use of the biospecific recognition avidin with the biotin from the SAM-terminals and biotinylated AChE, as well as the electrostatic interaction between silver nanoparticles with negatively charged citrate shell and avidin with encounter charge at pH 7.2. The construction process of the composite interface on gold was monitored by surface plasmon resonance (SPR), and its structure was characterized by attenuated total reflection Fourier-transform infrared spectra, atomic force microscopy and UV-vis spectra. The composite interface shows excellent electron transfer ability, as characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Under the optimum conditions a quantitative measurement of organophosphate pesticide dimethoate was achieved with the linear range of 0.05 mu M to10 mu M and the detection limit 0.01 mu M, taken as the concentration equivalent to a 10% decrease in signal. Silver nanoparticles conjugated biotin-avidin system represents a simple and functional approach to the integration of electrode sensing interface with improved biocompatibility and electron transfer ability, which may provide an analytical access to a large group of enzymes for bioelectrochemical application.