Resistive-Pulse Sensing and Surface Charge Analysis of a Single Nanoparticle Collision at a Conical Glass Nanopore

In this study, the collision of monodispersed single Au@SiO₂ nanoparticles (NPs; ∼83.5 ± 6.5 nm) at the outer orifice of a smaller-sized (∼40 ± 8 nm) conical glass nanopore was systematically investigated by the resistive-pulse sensing technique under three different surface charge states. When NPs approach the nanopipette orifice and collide, the ionic current changes dramatically, and the collision current amplitude shows a linear relationship with the potential bias applied. In our system, the electroosmotic flow is found to be the main driving force for the collision, and the resistive-pulse collision signal depends on the relative electroosmotic, electrophoretic, and electrostatic forces being applied, which in turn can reflect the surface charge properties of the tested NP and nanopore wall used. By fixing the size of the nanopore and NPs, the surface charge information on the NPs and nanopore walls can be discriminated by the magnitude and duration of the collision ionic current signals. This study manifested the feasibility of exploring the nanopore-based single NPs collision platform for surface charge analysis of the colloidal nanoparticle system.