Enhanced Electrochemiluminescence by Knocking Out Gold Active Sites

Electrochemiluminescence (ECL) of the conventional system of [Ru(bpy)₃]²⁺ luminophore and amine-based coreactants is particularly inefficient on noble metal electrodes. This is due to the formation of a passivating oxide layer on the metal surface inhibiting the electro-oxidation of amines like tri-n-propylamine (TPrA) coreactant. Herein, we demonstrated the enhancement of ECL emission on gold surface by hydroxyl radicals attack that are chemically generated with Cu-Fenton reagent. These radicals selectively deactivate the gold active sites and knockout the metal surface asperities that counterintuitively led to an amplification of the ECL emission. Atomic force microscopy shows a massive smoothening of the surface. The electrochemical characterization proves that the involved ECL reaction mechanism switches from direct oxidation to catalytic route, where the kinetics of indirect TPrA oxidation is facilitated on deactivated gold surface. Besides, in situ smoothening of a rough electrode in presence of tandem [Ru(bpy)₃]²⁺/TPrA enables Cu²⁺ sensing with good reliability and limit of detection. Such atomically smoothened and corrosion-resistant gold surface readily tuned the ECL reactivity and opened new directions on influence of topography and reactivity on ECL mechanisms, thus will be extremely useful for the future development of ECL imaging strategies and highly sensitive ECL sensors.