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

Wang, Bing, Xu, Yi-Tong, Lv, Jing-Lu, Xue, Tie-Ying, Ren, Shu-Wei, Cao, Jun-Tao, Liu, Yan-Ming, Zhao, Wei-Wei
Analytical chemistry 2019 v.91 no.6 pp. 3768-3772
alkaline phosphatase, aminophenols, ammonia, immunoassays, interleukin-6, lighting, oxidation, phosphates, phosphine, reducing agents
Herein we report an effective Ru(NH₃)₆³⁺/Ru(NH₃)₆²⁺-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)₆²⁺ 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)₆²⁺ by the photogenerated holes on the Bi₂S₃/BiVO₄ photoelectrode, starting the chain reaction in which the Ru(NH₃)₆²⁺ was regenerated by Ru(NH₃)₆³⁺-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)₆³⁺/Ru(NH₃)₆²⁺-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.