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 IrO 2 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-RuO 2, accelerate O 2 evolution, leading to luminescence quenching. Informed by the in situ spectroscopic measurements and theoretical calculations, we propose a mechanistic descriptor, [Δ G *O –2Δ G *OH ], to evaluate the balance between • OH accumulation and O 2 -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.