Signal-On Photoelectrochemical Immunoassay for Aflatoxin B1 Based on Enzymatic Product-Etching MnO2 Nanosheets for Dissociation of Carbon Dots
Aflatoxin B 1 (AFB 1 ) 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 1 in foodstuff. The immunoreaction was carried out on anti-AFB 1 antibody-modified magnetic beads by using glucose oxidase (GOx)-labeled AFB 1 -bovine serum albumin (AFB 1 –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 2 nanosheets. Accompanying the formation of immunocomplexes, the carried GOx initially oxidized the substrate (glucose) for the generation of H 2 O 2, which reduced/etched MnO 2 nanosheets into Mn 2+ ions, thereby resulting in the dissociation of CQDs from the electrode. Within the applied potentials, the photocurrent of MnO 2 -CQDs-modified electrode decreased with the increasing H 2 O 2 level in the detection cell. Meanwhile, a visual detection could be performed according to the change in the color of MnO 2 -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 1 within a dynamic working range from 0.01 to 20 ng mL –1 with a limit of detection (LOD) of 2.1 pg mL –1 (ppt). The developed immunoassay exhibited good reproducibility and acceptable accuracy. In addition, the method accuracy relative to AFB 1 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 1, it is easily extended to screen other small molecules or mycotoxins, thereby representing a versatile immunosensing scheme.