Cation Exchange Reaction-Mediated Photothermal and Polarity-Switchable Photoelectrochemical Dual-Readout Biosensor.

Cation exchange (CE) is a burgeoning method for controlled crystal synthesis; however, its applications in bioanalysis are still in their infancy. Herein, we explored the transformation of ZnInS in properties after the CE reaction with Cu ions; furthermore, the discrepancy was employed to design a dual-readout detection system of photothermal and polarity-switchable photoelectrochemical (PEC) immunoassays to realize reliable detection of carcinoembryonic antigen (CEA). In the presence of CEA, the CuO nanoparticles (CuO NPs) employed as dual-signal response probes would bond to the microplates and be acidolyzed by HCl to release Cu, which could replace Zn and In via the CE reaction. After the CE reaction is completed, the photocurrent would switch from a weak anodic photocurrent to a cathode one by using a 635 nm laser as a signal amplifier, while the photothermal signal would be enhanced with 808 nm laser illumination. On the basis of the polarity-switchable PEC strategy, CEA could be accurately detected from 0.1 to 50 ng mL with a limit of detection (LOD) of 48 pg mL (S/N = 3). Moreover, the photothermal assay for CEA detection possesses a linear range from 0.5 to 100 ng mL with a LOD of 0.21 ng mL. In addition, the designed sensing platform only relies on devices with portability that are permitted for point-of-care detection.