Etching reaction-based photoelectrochemical immunoassay of aflatoxin B1 in foodstuff using cobalt oxyhydroxide nanosheets-coating cadmium sulfide nanoparticles as the signal tags.

A new split-type photoelectrochemical (PEC) immunosensing platform was designed for sensitive detection of aflatoxin B1 (AFB1) in foodstuffs, coupling with enzymatic hydrolysate-triggered etching reaction of cobalt oxyhydroxide (CoOOH) on cadmium sulfide (CdS) nanoparticles-functionalized interface. Initially, the photosensitive electrode was prepared by coating CoOOH nanosheets on the surface of CdS nanoparticles to quench the photocurrent. Thereafter, a competitive-type enzyme immunoreaction was carried out on monoclonal anti-AFB1 antibody-conjugated magnetic bead by using alkaline phosphatase (ALP)-labeled bovine serum albumin-AFB1 (AFB1-BSA) conjugate as the competitor. With the formation of immunocomplex, the carried ALP hydrolyzed ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA) and phosphate. The former ascorbic acid produced etched or dissolved CoOOH nanosheets into Co2+ ions, thus resulting in the exposure of CdS nanoparticles on the surface to enhance the photocurrent of the modified electrode. Under optimum conditions, the photocurrent decreased linearly with the increasing AFB1 concentration in the dynamic range of 0.01-10 ng mL-1, and the limit of detection was 2.6 pg mL-1. The precision of this method (expressed as RSD) was ±8.6%. In addition, the accuracy was monitored by analyzing spiked food samples, and gave the well-matched results with the referenced ELISA method.