Nanocapillary Electrokinetic Tracking for Monitoring the Electrostatic Charge

We introduce nanoCapillary Electrokinetic Tracking (nanoCET), an optofluidic platform [1] for continuously measuring the electrophoretic mobility of a single colloidal nanoparticles or macromolecule in vitro with millisecond time resolution and high charge sensitivity. This platform is based on using a nanocapillary optical fiber in which liquids may flow inside a channel embedded inside the light-guiding core and nanoparticles are tracked using elastic light scattering. Using this platform we have experimentally measured electrophoretic mobility of single gold nanoparticles in an aqueous environment [2]. Further, using numerical simulation, we demonstrate the underlying electrokinetic dynamics inside the nanocapillary and the necessary steps for extending this method to probing single biomolecules, which can be achieved with existing technologies. This achievement will immensely facilitate the daunting challenge of monitoring biochemical or catalytic reactions on a single entity over a wide range of timescales. The unique measurement capabilities of this platform pave the way for a wide range of discoveries in colloid science, analytical biochemistry, and medical diagnostics.