Microtube Electrodes for Imaging the Electrochemiluminescence Layer and Deciphering the Reaction Mechanism.

Electrochemiluminescence (ECL) is a powerful transduction technique in biosensing and diagnostics, while mechanistic studies are still scarce. Herein we report the combined use of microtube electrode (MTE) and microscopy to measure the thickness of ECL layer (TEL) to decipher reaction mechanisms. For the classical system involving tris(2,2'-bipyridyl)ruthenium and tri-n-propylamine, the ECL pattern generated at the MTE tends to change from ring to spot upon increasing the luminophore concentration, with the TEL varying from ca. 3.1 μm to >4.5 μm. This variation is rationalized to arise from the contribution of the so-called catalytic route. While using 2-(dibutylamino)ethanol as the co-reactant, the ECL pattern remains ring-shaped and independent on the luminophore concentration. The TEL in this case is ca. 2.1 μm, implying that ECL generation is always surface-confined. MTEs can thus act as optical rulers for measuring the TEL and providing insightful mechanistic information.