Ru(NH3)63+/Ru(NH3)62+-Mediated Redox Cycling: Toward Enhanced Triple Signal Amplification for Photoelectrochemical Immunoassay

Herein we report an effective Ru(NH3)(6)(3+)/Ru(NH3)(6)(2+)-mediated photoelectrochemical-chemical-chemical (PECCC) redox cycling amplification (RCA) strategy toward enhanced triple signal amplification for advanced split-type PEC immunoassay application. Specifically, alkaline phosphatase (ALP) label was confined via a sandwich immunorecognition to convert 4-aminophenyl phosphate to the signal reporter 4-aminophenol (AP), which was then directed to interact with Ru(NH3)(6)(2+) as a redox mediator and tris (2-carboxyethyl) phosphine (TCEP) as reducing agent in the detection buffer. Upon illumination, the system was then operated upon the oxidation of Ru(NH3)(6)(2+) by the photogenerated holes on the Bi2S3/BiVO4 photoelectrode, starting the chain reaction in which the Ru(NH3)(6)(2+) was regenerated by Ru(NH3)(6)(3+)-enabled oxidization of AP to p-quinoneimine, which was simultaneously recovered by TCEP. Exemplified by interleukin-6 (IL-6) as the analyte, the Ru(NH3)(6)(3+)/Ru(NH3)(6)(2+)-mediated, AP-involved PECCC RCA coupled with ALP enzymatic amplification could achieve triple signal amplification toward the ultrasensitive PEC IL-6 immunoassay. This protocol can be extended as a general basis for other numerous targets of interest. Besides, we believe this work could offer a new perspective for the further exploration of advanced RCA-based PEC bioanalysis.