Bifunctional Moderator-Powered Ratiometric Electrochemiluminescence Enzymatic Biosensors for Detecting Organophosphorus Pesticides Based on Dual-Signal Combined Nanoprobes.

The bifunctional moderator is urgently needed in the field of ratiometric electrochemiluminescence (ECL) sensing since it can mediate simultaneously two ECL signals to conveniently realize their opposite change trend. This work designed a novel dual-signal combined nanoprobe with carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)--(1,4-benzo-{2,1',3}-thiadazole)] nanoparticles (-PFBT NPs) as the anodic ECL probe and -cysteine capped CdS quantum dots (-CdS QDs) as the cathodic ECL probe, which performed a dual-signal output capability without any additional coreactants. More importantly, hydrogen peroxide (HO) produced in situ by enzyme-catalyzed reaction was developed as a bifunctional moderator for simultaneously regulating two signals. The dual-signal combined nanoprobe (-PFBT NPs@CdS QDs) served as the matrix to immobilize acetylcholinesterase (AChE) and choline oxidase for organophosphorus (OPs) analysis. In the absence of OPs, HO was produced by catalyzing the substrate acetylthiocholine (ATCl) with enzymes and it quenched the anodic ECL signal from -PFBT NPs and simultaneously promoted the cathodic ECL signal from -CdS QDs. When OPs was present, the activity of AChE was inhibited, the anodic signal would increase, and the cathodic signal would accordingly decrease. The integration of the bifunctional moderator HO and dual-signal combined nanoprobe -PFBT NPs@CdS QDs not only provides an attractive ECL platform for enzymatic sensing involving the generation or consumption of HO but also paves a new pathway for other ratiometric ECL systems involving enzyme catalytic amplification for detecting antigens, antibodies, DNA, RNA, etc.