Sizing Individual Au Nanoparticles in Solution with Sub-Nanometer Resolution

Resistive-pulse sensing has generated considerable interest as a technique for characterizing nanoparticle suspensions. The size, charge, and shape of individual particles can be estimated from features of the resistive pulse, but the technique suffers from an inherent variability due to the stochastic nature of particles translocating through a small orifice or channel. Here, we report a method, and associated automated instrumentation, that allows repeated pressure-driven translocation of individual particles back and forth across the orifice of a conical nanopore, greatly reducing uncertainty in particle size that results from streamline path distributions, particle diffusion, particle asphericity, and electronic noise. We demonstrate similar to 0.3 nm resolution in measuring the size of nominally 30 and 60 nm radius Au nanoparticles of spherical geometry; Au nanoparticles in solution that differ by similar to 1 nm in radius are readily distinguished. The repetitive translocation method also allows differentiating particles based on surface charge density, and provides insights into factors that determine the distribution of measured particle sizes.