We describe the electrochemical detection of single nanoparticle (NP) attachment on a nanoelectrode by the increase in the active electrode area. The attachment of gold NP-decorated single wall carbon nanotubes (Au-SWCNTs) was observed by their current time transients for ferrocenemethanol (FcMeOH) oxidation. Since the attached Au-SWCNT increases the electroactive area available for FcMeOH oxidation, the current increases after attachment of the particle. The "staircase" shape of the current response establishes that the particles do not become deactivated for the outer-sphere electron transfer reaction after attachment. Au-SWCNTs migrate to and are held at the nanoelectrode by an electric field. However, SWCNTs that are not decorated with a gold NP produce only a sharp transient ("blip") response.