Studying electrocatalytic metal nanoparticles (NPs) at the single particle level is highly desirable to unfold their structure-function correlation. In this report, we present the fabrication and spectroelectrochemistry characteristics of light-scattering single Au NP at the tip of an electrochemically etched sharp tungsten (W) electrode. Au NPs with a tunable particle size (>= 60 nm) can be obtained at the Wtips by adjusting the Au electrodeposition conditions. Catalyzed electrogenerated chemiluminescence (ECL) from Tris(2,2'-bipyridine) ruthenium (II) (Ru(bpy)(3)(2+))/ Tri-n-propylamine (TPrA) system at single Au NP electrode shows an increase in its intensity with Au NP particle size in the range of 300 nm-500 nm. The potential application of these single Au NP electrodes in the studies of electrocatalytic reaction and spectroelectrochemistry at the nanometer scale is demonstrated using dark-field scattering (DFS) spectroelectrochemistry method. The decrease in DFS intensity upon oxidation of hydrazine at the single Au NP electrode is attributed to the formation of low-refraction-index N-2 near the surface of the Au NP to decrease its light scattering cross-section. Single Au NP electrode presented in this work would help improve instrument capability of scanning electrochemical microscope (SECM) and near-field scanning optical microscope (NSOM) techniques for ultrasensitive electrochemical analysis. (C) 2018 Elsevier Ltd. All rights reserved.