Self-supply of H2O2 and O2 by hydrolyzing CaO2 to enhance the electrochemiluminescence of luminol based on closed bipolar electrode.

Li, Xiaojian; Du, Yu; Wang, Huan; Ma, Hongmin; Wu, Dan; Ren, Xiang; Wei, Qin; Xu, Jing-Juan

A novel luminol electrochemiluminescence (ECL) sensing platform was developed based on indium tin oxide closed bipolar electrode (ITO BPE) for detecting biomarkers of squamous cell carcinomas named cytokeratin 19 fragments (CYFRA 21-1). A strategy of in-situ generated coreactant H2O2 and O2 was proposed to enhance luminol ECL intensity. CaO2, possessing a high capacity of self-supplying H2O2 and O2, was encapsulated by ZIF-67, glucose oxidase and horseradish peroxidase (GOD/HRP-loaded ZIF-67@CaO2). In the presence of glucose, gluconic acid and H2O2 were generated via the catalytic effect of GOD, then gluconic acid can induce the degradation of ZIF-67 leading to the unprotected CaO2 hydrolyzing to produce both O2 and H2O2. Therefore, generated coreactant O2 and H2O2 via the oxidation of glucose and the hydrolysis of CaO2 can effectively enhance luminol ECL behavior. According of luminol ECL reaction occurring on the anode surface of ITO BPE, a sandwich immunosensor was fabricated on the anodic ITO BPE and GOD/HRP-loaded ZIF-67@CaO2 as labels incubated with secondary antibodies. Owing to the cathodic reaction rate influencing the anodic reaction rate, Au nanoparticles were electro-deposited on the cathode surface of ITO BPE, which not only meliorated oxygen reduction, but also further enhanced the ECL intensity of luminol. Under optimal experiments, the ECL immunosensor for detecting CYFRA 21-1 with a wider linear range from 0.0075 to 50 ng mL-1 and a detection limit of 1.89 pg mL-1 (S/N = 3) was obtained.