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

A convenient, specific, and highly sensitive electrochemical immunosensor based on an 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 an 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.