Oxygen Activation Biocatalytic Precipitation Strategy Based on a Bimetallic Single-Atom Catalyst for Photoelectrochemical Biosensing

The traditional biocatalytic precipitation (BCP) strategy often required the participation of H₂O₂, but H₂O₂ had the problem of self-decomposition, which prevented its application in quantitative analysis. This work first found that a bimetallic single-atom catalyst (Co/Zn-N-C SAC) could effectively activate dissolved O₂ to produce reactive oxygen species (ROS) due to its superior oxidase (OXD)-like activity. Experimental investigations demonstrated that Co/Zn-N-C SAC preferred to produce highly active hydroxyl radicals (^•OH), which oxidized 3-amino-9-ethyl carbazole (AEC) to produce reddish-brown insoluble precipitates. Based on this property, a unique oxygen-activated photoelectrochemical (PEC) biosensor was developed for chloramphenicol (CAP) detection. Cesium platinum bromide nanocrystals (Cs₂PtBr₆ NCs) were a new type of halide perovskite with lead-free, narrow band gaps, and water-oxygen resistance. Cs₂PtBr₆ NCs showed excellent cathodal PEC performance without an exogenous coreactant and were first used for PEC detection. As a "proof-of-concept application", Co/Zn-N-C SAC was introduced onto the surface of Cs₂PtBr₆ NCs by using the CAP dual-aptamer sandwich strategy. Co/Zn-N-C SAC activated dissolved O₂ to produce ROS, which oxidized AEC to produce precipitates, quenching the cathodal PEC signal of Cs₂PtBr₆ NCs for CAP detection. In summary, this work first used SAC to overcome the restriction of the traditional enzymatic BCP strategy requiring H₂O₂, improved the stability and accuracy of quantitative analysis, and also broadened the application range of coreactant-free perovskite-type PEC biosensors.