A Novel Label-free Immunosensor Based on L-cysteine/deposited Gold Nanocrystals for the Chlorpyrifos Detection

In this paper, a novel label-free immunosensor for the chlorpyrifos residues detection was developed. This immunosenor was based on deposited gold nanocrystals (DpAus)/L-cysteine (L-Cys) modified Au electrode. The DpAus was used due to its unique properties: large surface and good conductivity, improve the performance of the electrode surface, rise the sensitivity of the current responsive. L-cysteine and DpAus were combined through Au-S bond. The immobilization of chlorpyrifos antibodies at the gold electrode was carried out through a stable acyl amino ester intermediate generated by 1-ethyl-3-(3-dime thylaminoprop-yl) carbodiimide (EDC) and N-hydrosuccinimide (NHS), which could condense antibodies highly efficient and immobilize them orientedly on the Au electrode surface. The sensitive steps of surface modification had been characterized by cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS), respectively. The immunoreaction between anti-chlorpyrifos monoclonal antibody and chlorpyrifos directly triggered a signal via different pulse voltammetry (DPV). Then we optimized conditions during the preparation of the immunosensor. The result was: the optimized pH of the working solution was 7.5, the optimized cubation time was 25 min. Under optimal conditions the immunosensor showed good response to chlorpyrifos, the rate of the peak current change of the biosensor were in linear with concentrations of chlorpyrifos from 1.0 to 200.0 ng/mL with a detection limit 0.17 ng/mL