A multi-colorimetric immunosensor for visual detection of ochratoxin A by mimetic enzyme etching of gold nanobipyramids.

A multi-colorimetric immunosensor basing on the mimetic enzyme etching of gold nanobipyramids (Au NBPs) was established to detect ochratoxin A (OTA). Octahedral Cu2O nanoparticles were successfully synthesized through a selective surface stabilization strategy, which can exhibit a peroxidase-like ability to oxidize 3,3',5,5'-tetramethylbenzidine (TMB). Au NBPs can be etched by the product, TMB2+, to form a significant longitudinal peak blue shift of local surface plasmon resonance. During the construction of the immunosensor, the microplate was coated with dopamine to immobilized OTA antigens, followed by the immunoreaction of OTA antibody and the Cu2O-labled secondary antibody. A linear relationship can be found between the local surface plasmon resonance (LSPR) peak changes with the logarithm of OTA concentration in a wide range from 1 ng/L to 5 µg/L, while the detection limit was 0.47 ng/L. Meanwhile, the approximate OTA concentration can be conveniently and intuitively observed by the vivid color changes. Benefiting from the high specificity, the proposed multi-colorimetric immunoassay detection of OTA in millet samples was achieved, indicating the available potential of the immunoassay for the determination of OTA in real samples.