Two orders-of-magnitude enhancement in the electrochemiluminescence of Ru(bpy)₃²⁺ by vertically ordered silica mesochannels.

In this paper, we report significantly enhanced electrochemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) at indium tin oxide (ITO) electrodes modified with a thin film consisting of vertically aligned silica mesochannels (SMCs). The perpendicular SMCs allow for the effective mass transport of Ru(bpy)₃²⁺ and its co-reactants from the solution to the underlying ITO electrode surface. Moreover, due to the ultrasmall diameter (namely 2-3 nm) and the negatively charged surface, SMCs exerted a strong electrostatic attraction to the positively charged Ru(bpy)₃²⁺ to accelerate its mass transport, resulting in a remarkably increased ECL signal. As a model system, when using tri-n-propylamine (TPrA) as the co-reactant, the intensity of ECL generated at the SMCs-modified ITO electrode was stronger than that at a bare ITO electrode by more than two orders of magnitude (i.e., ∼107-fold increase). In this case, the amount of Ru(bpy)₃²⁺ required for ECL-based analysis can be considerably reduced. A very low concentration of Ru(bpy)₃²⁺, namely 9 μM, was demonstrated to be enough for achieving the sensitive detection of TPrA, nicotine and atropine. Both photomultiplier (PMT) and charge coupled device (CCD) were used to measure the luminescence from the ECL reaction. The obtained detection limits were 0.17 nM for TPrA on the basis of the ECL intensity measurement, 72 nM for nicotine and 38 nM for atropine based on the gray value analysis of captured ECL images.