Colorimetric and photothermal dual-mode immunoassay of aflatoxin B1 based on peroxidase-like activity of Pt supported on nitrogen-doped carbon

Abstract

In this work, a split-type dual-mode (colorimetric/photothermal) immunoassay method was designed for point-of-care testing (POCT) detection of mycotoxins (aflatoxin B1, AFB1 as the model analyte) in foodstuffs based on Pt supported on nitrogen-doped carbon amorphous (Pt-CN). The as-synthesized Pt-CN exhibits excellent peroxidase-mimicking activity, which can catalyze the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB) into TMBox with sensitive colorimetric readout in the presence of hydrogen peroxide (H2O2). Moreover, the TMBox also serves as a near-infrared (NIR) photothermal agent to convert the colorimetric readout into heat under the irradiation of an 808 nm laser. A competitive-type immunoreaction is carried out between AFB1 and glucose oxidase (GOx)-labeled AFB1-bovine serum albumin (AFB1-BSA-GOx) conjugates. With the formation of immune complexes, the entrained GOx catalyzes the hydrolysis of glucose to generate H2O2, which further involves the Pt-CN catalyzed production of TMBox to increase colorimetric/photothermal readouts. Depending on the degree of TMB oxidation, the dual-mode immunoassay provides a linear range of 1.0 pg/mL to 10 ng/mL, with a limit of detection (LOD) of 0.22 pg/mL for the colorimetric assay and 0.76 pg/mL for the photothermal assay. Moreover, the developed method is successfully used to detect AFB1 in peanuts with acceptable accuracy compared with commercially enzyme-linked immunosorbent assay (ELISA) kits. Significantly, the photothermal readout in this method is recorded on a mobile phone device without any expensive instruments, providing an affordable and convenient tool for food safety testing.