Using chronoamperometry, it is possible to detect the adsorption events of single nanoparticles at an ultramicroelectrode(UME).1,2When a nanoparticle strikes the electrode surface, it blocks part of the electroactivearea, resulting in a decrease to the electrode current. The extent to which UME surface properties affect the nanoparticle response is still poorly understood. This research compared collision data for polystyrene nanoparticles using a solid Pt UME to new experiments using a Hg UME. Blocking of the electrode area by nanoparticles was detected at the Hg UME, although individual particle impacts could not be resolved, possibly due to mobility of the particles on the Hg surface. The electrodes used were also characterized using cyclic voltammetry (CV).