Detection of single metal nanoparticle collision events in non-aqueous media

In this work, the detection of metal nanoparticle collision events in a non-aqueous solvent-here, toluene and acetonitrile-using gold nanoparticles and a platinum ultramicroelectrode (UME) is reported. The collisions were monitored by the oxidation of tri-n-propylamine (TPrA) under diffusion-dominated conditions. Based on the current response, it was observed that the current steps were indicative of a mediated Faradaic reaction. Current steps as small as 1-2 pA could be clearly observed. Larger current steps were caused by agglomeration of the nanoparticles attributed to the polarity of the mixed solvent. The experimentally observed collisions per second ranged from 0.07 to 0.51, indicating that particle agglomeration in solution occurs rapidly, reversibly and can subsequently cause rapid and, often, repeated collisions.