Bifunctional TEMPO-based catalysis boosts luminol electrochemiluminescence for cholesterol sensing

Electrochemiluminesence (ECL) of luminol has been enhanced through the catalysis of various artificial nanomaterials to improve its performance in sensing applications. Herein, we report on a biofunctional-catalytic approach based on a simple organic radical, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), which enhances significantly the ECL emission for both luminol/O2 and luminol/H2O2 systems. The electrochemical studies showed that TEMPO could be oxidized to highly stable oxoammonium cation (TEMPO+) without any interferences of dissolved O2, but was found to improve the oxidation of luminol. On the other hand, TEMPO as an electrocatalyst could make the oxidation of H2O2 more efficient. This bifunctional-catalysis of TEMPO has facilitated the production of L−• in luminol/dissolved O2 system and O2−• in luminol/H2O2 system for ECL generation. Based on the enhanced ECL of luminol/TEMPO/cholesterol oxidase (ChOx)/cholesterol system, an ECL sensor has been designed for the selective and sensitive detection of cholesterol with a linear range between 0.30 μM and 100 μM and a low detection limit of 0.08 μM. Finally, the present work opens new avenues for studying luminol ECL using the bifunctional-catalysis of nitroxyl radicals.