Resistive Pulse Delivery of Single Nanoparticles to Electrochemical Interfaces

An experimental system for controlling and interrogating the collisions of individual nanoparticles at electrode/electrolyte interfaces is described. A nanopipet positioned over a 400 nm radius Pt ultramicroelectrode is used to deliver individual nanoparticles, via pressure-driven solution flow, to the underlying electrode, where the nanoparticles undergo collisions and are detected electrochemically. High-velocity collisions result in elastic collisions of negatively charged polystyrene nanospheres at the Pt/water interface, while low-velocity collisions result in nanoparticle adsorption ("sticky" collisions). The ability to position the nanopipet with respect to the underlying ultramicroelectrode also allows the time between particle release from the nanopipet and electrode collision to be investigated as a function of nanopipet-electrode separation, d. The time between release and collision of the nanoparticle is found to be proportional to d³, in excellent agreement with an analytical expression for convective fluid flow from a pipet orifice.