Water Activation Enables Low-Triggering-Potential [Ru(bpy)3]2+-Tripropylamine Electrochemiluminescence

Low-triggering-potential electrochemiluminescence (ECL) systems based on tris(2,2'-bipyridyl) ruthenium(II)/tripropylamine ([Ru(bpy)3]2+/TPrA) are essential for minimizing electrochemical interference and enabling highly sensitive biodetection. However, the practical application of these systems is constrained by the requirement for high concentrations of the coreactant TPrA (∼100 mM), which poses cytotoxicity concerns, and by the inherently sluggish kinetics of TPrA electrooxidation at the electrode interface. Here, we introduce a water activation strategy to generate hydroxyl radicals (•OH) in situ, which mediate the spontaneous chemical oxidation of TPrA, thereby bypassing the need for direct electrooxidation. By modulating water activation efficiency across a series of prototype metal oxides, we demonstrate that kinetic hysteresis in IrO2 with its moderate oxygen evolution reaction (OER) activity facilitates •OH accumulation, significantly enhancing TPrA oxidation at a low onset potential of 0.66 V, corresponding to about a 0.1 V negative shift relative to the conventional direct TPrA oxidation pathway (∼0.75 V). In contrast, highly active OER catalysts, such as grain-boundary-RuO2, accelerate O2 evolution, leading to luminescence quenching. Informed by the in situ spectroscopic measurements and theoretical calculations, we propose a mechanistic descriptor, [ΔG*O-2ΔG*OH], to evaluate the balance between •OH accumulation and O2-induced quenching. This framework enables the rational screening and design of catalysts for efficient ECL emission. Leveraging this approach, we further develop a robust and selective biosensor for the detection of acetamiprid, demonstrating the practical utility of the strategy.