Ultrasensitive electrochemical immunosensor for ochratoxin A using gold colloid-mediated hapten immobilization

A convenient, specific, and highly sensitive electrochemical immunosensor based Oil all indirect competitive assay format was developed for the determination of ochratoxin A (OTA), a common toxic contaminant in various kinds of agricultural products The sensing substrate was prepared Using a gold electrode modified with a self-assembled monolayer of 1,6-hexanedithiol that mediated the assembly of a gold colloid layer, which could enhance the Surface loading of OTA-ovalbumin conjugate and improve the sensitivity in electrochemical readouts. After competition of the limited anti-OTA mouse monoclonal antibody between immobilized hapten and OTA analyte in sample solution, alkaline phosphatase (ALP)-labeled horse anti-mouse immunoglobulin G (IgG) antibody was selectively bound onto the surface of the electrode, affording all indicator for OTA concentration in the sample. Electrochemical response arising from the oxidation of enzymatic product of 1-naphthyl phosphate was observed to be inversely proportional to OTA concentration in the range from 10 pg/ml to 100 ng/ml with a detection limit as low as 8.2 pg/ml. Furthermore, a negligible matrix effect and good recoveries were obtained in the determination of corn samples, evidencing the feasibility of the proposed method for accurate determination of OTA in corn samples. (C) 2009 Published by Elsevier Inc.