Electrochemiluminescence Microscopy Imaging Using Ru(bpy)3 2+ Doped in Silica Microspheres

Abstract

Electrochemiluminescence (ECL) is a controllable form of chemiluminescence where emission intensity is affected by a voltage imposed at an electrode surface. ECL microscopy imaging is a imaging technique aimed at light-emitting close to electrode surface with highly temporal and spatial resolution. Because ECL emitters are generated in situ at electrode surfaces, ECL imaging reflects the local surface reactivity and has a near-zero background. These features make ECL very useful in imaging applications, such as multiplexed ECL sandwich immunoassays, parallel single-cell analysis and latent fingerprints ECL imaging. Here we synthesized Ru(2,2’-bipyridine)3Cl2-doped silica (RuDS) microspheres via Stober method for single microsphere ECL imaging. The RuDS microsphere consisted of a silica core and a Ru(2,2’-bipyridine)3Cl2-doped silica shell via sol−gel process to immobilize Ru(bpy)3Cl2 into silica shell. Rougher sufaces and some defects indicated imperfect growth of Ru(2,2’-bipyridine)3Cl2-doped silica shell. We also noticed that RuDS microspheres tended to aggregate in the growth of Ru(2,2’-bipyridine)3Cl2-doped silica shell, since electrostatic interaction between Ru(bpy)3Cl2 and silica matrices decreased negatice charges on the surfaces of silica microspheres. Then an electrode modified with RuDS microspheres was placed in a cell under the microscope. The bright field image showed the positions of the RuDS microspheres. The bright ECL image of RuDS microspheres suggested that intermediates generated by electrooxidation of tripropylamine (TPA) can move up to several micron to cause the excitation of Ru(bpy)3Cl2. Interestingly, the ECL intensity from different single microspheres exhibited obvious distinctions, which may derive from local heterogeneity of electrode surface and RuDS microspheres. Moreover, the image sequences showed the areas without any microspheres also produced a weak ECL background signal, as a result of the electrooxidation of TPA itself. Simultaneously, the oxidation current of TPA in cyclic voltammetry and the ECL emission intensity of RuDS microspheres dramatically decreased along with increase of scan times, indicating the passivating of the surface of electrode was occured when the potential was applied. These results demonstrated that ECL microscopy imaging of single RuDS microsphere appearing high temporal and spatial resolution, is a powerful tool in terms of further understanding of detailed ECL mechanisms, both emiters and coreactants, and potential application in single molecule detection, etc.