Pt Nanoparticle Collisions Detected by Electrocatalytic Amplification and Atomic Force Microscopy Imaging: Nanoparticle Collision Frequency, Adsorption, and Random Distribution at an Ultramicroelectrode Surface

We demonstrate good agreement between the theoretical and experimental collision frequency of individual Pt nanoparticles (NPs) undergoing collisions at a Au ultramicroelectrode (UME) (5 μm radius) using electrocatalytic amplification provided by 15 mM hydrazine in 5 mM phosphate buffer (PB; pH 7) over 100 to 300 s. Dynamic light scattering (DLS) measurements demonstrated that Pt NP aggregation in this solution had the least impact on NP diffusion coefficient and concentration values, which are directly proportional to collision frequency. We show that the smaller, uniform current steps are indicative of NPs of metallic radii in agreement with those determined by transmission electron microscopy (TEM), with corresponding larger NP diffusion coefficient and concentration, in agreement with DLS results. These contribute to the larger NP collision frequency observed experimentally. Using atomic force microscopy (AFM) imaging, we show good agreement between the number of NPs imaged on the UME surface and the ...