Self-enhanced electrochemiluminescence: Moxifloxacin as a bifunctional coreactant and target in Ru(bpy)32+-based pharmaceutical sensing

Analyte-induced self-enhanced electrochemiluminescence (ECL) is a powerful strategy for simplifying ECL sensing and improving the overall sensitivity without the addition of external coreactants. However, most Ru(bpy) 3 2+ -based ECL systems still rely on external coreactants such as tri- n -propylamine (TPrA) or oxalate, which introduce additional reagents and increase assay complexity. Herein, we report that the moxifloxacin (MFX) can intrinsically function as an efficient coreactant for Ru(bpy) 3 2+ , enabling an external-coreactant-free and self-enhanced ECL system for its sensitive detection. Electrochemical and ECL investigations reveal that MFX participates directly in the ECL pathway through anodic oxidation, generating reactive intermediates that efficiently trigger the excited Ru(bpy) 3 2+ * state. As a result, the Ru(bpy) 3 2+ –MFX system generates ∼17-fold higher ECL intensity than the classical oxalate system and a comparable ECL response to TPrA (∼66%) under identical conditions. Leveraging this intrinsic self-amplification, an ECL method was developed for sensitive and selective detection of MFX. The developed method exhibits two linear dynamic ranges (0.05–200 μM and 200–800 μM) with a limit of detection (LOD, S/N = 3) of 36 nM. The proposed method offers excellent sensitivity, reproducibility, and selectivity against common interferents and ophthalmic excipients. Moreover, validation using commercial ophthalmic formulations demonstrated excellent agreement with HPLC results, supporting the accuracy of the developed method for pharmaceutical quality control. By integrating analyte recognition and signal generation into a single molecular entity, this work opens a new pathway toward simple and green self-enhanced ECL sensing platforms.