In Situ Ultrasound Irradiation for Regulating the Electrochemiluminescence Intensity and Layer

Electrochemiluminescence (ECL) has manifested a surface-confined emitting character and a low light background occurring near the electrode surface. However, the luminescence intensity and emitting layer are limited by the slow mass diffusion rate and electrode fouling in a stationary electrolyte. To address this problem, we developed an in situ strategy to flexibly regulate the ECL intensity and layer thickness by introducing an ultrasound (US) probe to the ECL detector and microscope. Herein, we explored the ECL responses and the thickness of ECL layer (TEL) under US irradiation in different ECL routes and systems. ECL microscopy with an ultrasonic probe discovered that ultrasonic radiation enhanced the ECL intensity under the catalytic route, while an opposite trend was observed under the oxidative-reduction route. Simulation results demonstrated that US promoted the direct electrochemical oxidation of TPrA radicals by the electrode rather than oxidant Ru(bpy)33+, which made the TEL thinner than that in the catalytic route under the same US condition. In situ US boosted the ECL signal from 1.2 times to 4.7 times by improving the mass transport and weakening electrode fouling due to the cavitation role. It significantly enhanced the ECL intensity beyond the diffusion-controlled ECL reaction rate. In addition, a synergistic sonochemical luminescence is validated in the luminol system to enhance the whole luminescence because cavitation bubbles of US promoted the generation of reactive oxygen species. This in situ US strategy provides a new opportunity to understand ECL mechanisms and a new tool in regulating TEL to meet the needs of ECL imaging.