Electrochemiluminescence Self-Interference Spectroscopy with Vertical Nanoscale Resolution

Here we report an electrochemiluminescence (ECL) self-interference spectroscopy technique (designated as ECLIS) with spatial resolution in the normal direction of the electrode surface. Self-interference principally originates from the superposition of ECL emitted directly by luminophores and that reflected from electrode surfaces, resulting in a spectrum consisting of orderly distributed peaks. On the basis of this spectrum and theoretical analysis by the matrix propagation model, the distance between luminophores and the electrode surface can be probed with a vertical resolution on the nanometer scale. We demonstrated first in this work that the height of ECL luminophores assembled on the electrode surface using different molecular linkers, such as double-stranded DNA, could be determined, as well as the possible conformation of linker molecules at the surface. Moreover, the thickness of the ECL emitting layer adjacent to the electrode surface was estimated for the classical coreactant ECL systems involving freely diffusing Ru(bpy)32+ and tri-n-propylamine in solutions. The thickness was found to vary from ∼350 nm to nearly 1 μm depending on the concentration of Ru(bpy)32+. We believe that ECLIS with a high vertical resolution will provide an easy way to collect molecular conformation information and study ECL reaction mechanisms at electrode interfaces.