Remarkably enhanced oxidase-mimic activity based on AuAg NCs-modified 0D/2D P-N heterojunction nanozyme for ultra-sensitive detection of ochratoxin A by colorimetric and ratio fluorescence dual-mode

Ochratoxin A (OTA) is a representative foodborne fungal toxin that poses great harm to humans, the ultra-sensitive detection of OTA is an urgent requirement for public health. In this work, a competitive colorimetric and ratio fluorescence dual-mode immunosensor for the detection of OTA based on 0D/2D AuAg NCs/SPCN/BGQDs heterojunction nanozyme was devised and fabricated. The presence of P-N heterojunctions was confirmed through electrochemistry and theoretical calculations, heterojunction formed between AuAg NCs-SPCN and BGQDs effectively augmented the oxidase-mimic activity, verified by enzyme kinetic analysis. Superoxide radicals (·O2-) were catalyzed by heterojunction nanozyme from dissolved oxygen, and o-phenylenediamine was oxidized by ·O2- to produce diaminophenazine. It exhibited an absorption peak at 450 nm overlapped with the emission peak of heterojunction nanozyme. The fluorescence at 434 nm was quenched through the IFE effect while the fluorescence at 565 nm was enhanced and accompanied by solution yellowing, so ratio fluorescence was formed due to two emission peaks and the dual-mode detection system was constructed. The dual-mode immunosensor exhibited exemplary linearity across the concentration span of 0.001–20 μg/L, with LODs of 0.28 ng/L (ratio fluorescence) and 0.2 ng/L (colorimetry) respectively. Therefore, this immunosensor demonstrated potential applications in food quality testing and visual analysis.