Solid-State 3D Electrochemiluminescence Platform: Depth-Tuned Ru Complexes Positioning for Label-Free High-Resolution Imaging

This study introduces a solid-state three-dimensional electrochemiluminescence (ECL) platform based on a mesoporous TiO2 superstructure deposited onto a fluorine-doped tin oxide (FTO) electrode and covalently functionalized with phosphonated [Ru(bpy)2(Pbpy)]2+ complexes via zirconium phosphate (ZP) priming. By precisely controlling the vertical separation (L2) between immobilized luminophores and the underlying electrode, we uncover a depth-dependent ECL mechanism in which tripropylamine (TPrA) oxidation is driven selectively through a catalytic pathway. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirms precise control over the vertical distribution of the luminophore, while electrochemical measurements reveal redox activity of immobilized Ru complexes mediated through the oxide scaffold. The platform further enables label-free shadow ECL imaging, in which localized perturbation of the catalytic ECL process generates high-contrast emission patterns. This architecture establishes a strategy for designing label-free ECL microscopy platforms featuring selective emission pathways and enhanced spatial resolution.