Biochemical reaction-regulated electrocatalytic bipolar electrochemiluminescence platform with immobilization-free and exogenous electroactive-species-free sensing for cholesterol detection.

A biochemical reaction-regulated electrocatalysis strategy for quantitative cholesterol detection using platinum nanoparticle-functionalized indium tin oxide electrodes for electrochemiluminescence. In this system, cholesterol is oxidized by cholesterol oxidase to generate H2O2 in situ, which serves as an endogenous electroactive species and undergoes reduction at the BPE cathode. According to the charge balance principle, the cathodic reaction drives the anodic oxidation of the Ru(bpy)32+/TPrA system, generating an ECL signal that correlates quantitatively with cholesterol concentration. PtNPs at the BPE cathode enhance the electrocatalytic reduction of H2O2 and accelerate interfacial electron transfer, leading to an amplified anodic ECL response. Under optimized conditions, the platform exhibits a linear range of 0.1-10 mM with an extrapolated detection limit of 98.4 µM. The proposed sensing strategy was successfully applied to cholesterol detection in human serum samples, demonstrating good accuracy and anti-interference capability. Notably, the ChOx-catalyzed oxidation of cholesterol proceeds homogeneously in the sensing solution, while no enzyme-immobilization step is required during sensor preparation. In addition, no externally added electroactive species are required in the sensing cell, while the Ru(bpy)32+/TPrA ECL system is confined to the reporting cell. This sensing/reporting separation effectively minimizes cross-interference.