How to replace the oil droplet in Millikan's experiment with a single virus

A highly sensitive optical capillary electrophoresis measurement method based on a nanofluidic optical fiber platform is presented. By using scaling arguments and considering realistic instrument limitations, I underline the feasibility of measuring the electrophoretic mobility of a single freely-diffusing nanoparticle or macromolecule in vitro, continuously and indefinitely, with microsecond time resolution. The high speed of this technique opens up new possibilities for studying reaction kinetics at the single molecule level.