An Electro-Fenton-Driven Self-Ratio Electrochemiluminescence Sensing Platform without a Coreactant for Sensitive and Accurate Monitoring of Antibiotics

A ratiometric electrochemiluminescence (ECL) sensor with a self-calibration function can significantly enhance the detection accuracy of analytes. However, the requirement for two suitable ECL emitters and their corresponding coreactants often limits its practical applicability. In this study, luminol was employed as a single ECL emitter combined with the electro-Fenton strategy to construct a ratiometric ECL sensor without exogenous coreactants. The NiCo-MOF (NC-MOF) acted as both a suitable catalyst for the oxygen reduction reaction (ORR) and a metal source, initiating the electro-Fenton reaction to generate hydroxyl radicals (OH•) and superoxide anions (O2•-), which enhanced the cathodic and anodic ECL emissions of luminol, respectively. The aptamer for the target antibiotics and its complementary strand was immobilized on the NC-MOF-based electrode, which also served as a scaffold for the in situ growth of palladium nanoparticles (Pd NPs). Target binding induced the release of the aptamer from the electrode, causing unwinding of the double-stranded DNA (dsDNA) and retention of the complementary single strand. This results in the recovery of anodic ECL emission and simultaneous suppression of the cathodic ECL signal, since Pd NPs transform O2•- into OH•, and the content of immobilized Pd NPs decreases as dsDNA unwinds. Using kanamycin (KAN) as a model analyte, quantitative detection was achieved by changing the ECL intensity ratio (Ianodic/Icathodic). To improve the sensor performance in complex natural water samples and extend its service life, bovine serum albumin@2-(Methacryloyloxy)ethyl 2-(Trimethylammonio)ethyl Phosphate (BSA@MPC) was integrated to mitigate nonspecific adsorption of interfering substances such as bacteria and proteins. The ratiometric ECL sensor exhibits a wide detection range (10 pM-100 μM), a low detection limit (4.81 pM, S/N = 3), and excellent antifouling properties. Additionally, the sensor successfully detects KAN in natural water samples, with results comparable to high-performance liquid chromatography (HPLC) analysis, demonstrating its potential for trace antibiotic detection in complex environmental matrices.