Electrochemically Driven Luminescence without Liquid Electrolyte: A Sensing Platform via Eutectic Gallium−Indium Solid-State Junctions

Electrochemiluminescence (ECL) is a powerful sensing technique but typically relies on liquid electrolytes and multi-electrode configurations, limiting device miniaturization and integration. Here, we report a solid-state electrochemically driven luminescent sensing platform based on two-electrode junctions comprising an indium tin oxide bottom electrode, a Ru(bpy)32+−TPrA@Nafion active layer (TPrA: tripropylamine), and a soft eutectic gallium−indium (EGaIn) top electrode. Nafion serves as a porous host matrix that immobilizes the luminophore and co-reactant while facilitating analyte uptake, whereas EGaIn provides a simple conformal electrical contact for solid-state operation. Despite the absence of a liquid electrolyte during electrical excitation, the junctions retain key characteristics of classical Ru(bpy)32+ electrochemistry. The luminescence is enhanced by the co-reactant TPrA and quenched by dopamine (DA), enabling quantitative sensing based on modulation of the emission intensity. The platform exhibits a linear response to dopamine over a concentration range of 1.0 × 10−10−1.0 × 10−4 M with a detection limit of 5.1 × 10−11 M, together with excellent reproducibility, selectivity, operational stability, and satisfactory recovery in human serum samples. These results demonstrate that ECL-inspired sensing chemistry can be implemented in a solid-state device architecture, providing a promising strategy for integrated luminescent sensing platforms and miniaturized analytical devices.