Signal-On Photoelectrochemical Immunoassay for Aflatoxin B Based on Enzymatic Product-Etching MnO Nanosheets for Dissociation of Carbon Dots.

Aflatoxin B (AFB) monitoring has attracted extensive attention because food safety is a worldwide public health problem. Herein, we design a novel simultaneously visual and photoelectrochemical (PEC) immunosensing system for rapid sensitive detection of AFB in foodstuff. The immunoreaction was carried out on anti-AFB antibody-modified magnetic beads by using glucose oxidase (GOx)-labeled AFB-bovine serum albumin (AFB-BSA) conjugates as the tags with a competitive-type immunoassay format, while the visual and PEC evaluation was performed via carbon quantum dots (CQDs)-functionalized MnO nanosheets. Accompanying the formation of immunocomplexes, the carried GOx initially oxidized the substrate (glucose) for the generation of HO, which reduced/etched MnO nanosheets into Mn ions, thereby resulting in the dissociation of CQDs from the electrode. Within the applied potentials, the photocurrent of MnO-CQDs-modified electrode decreased with the increasing HO level in the detection cell. Meanwhile, a visual detection could be performed according to the change in the color of MnO-CQDs-coated electrode. To elaborate, this system was aggregated into a high-throughput microfluidic device to construct a semiautomatic detection cell. Under optimal conditions, the photocurrent increased with the increasing target AFB within a dynamic working range from 0.01 to 20 ng mL with a limit of detection (LOD) of 2.1 pg mL (ppt). The developed immunoassay exhibited good reproducibility and acceptable accuracy. In addition, the method accuracy relative to AFB ELISA kit was evaluated for analyzing naturally contaminated or spiked peanut samples, giving the well-matched results between two methods. Although our strategy was focused on the detection of target AFB, it is easily extended to screen other small molecules or mycotoxins, thereby representing a versatile immunosensing scheme.