Abstract
We developed a novel measurement method of flow velocity distribution in nanochannels exploiting defocusing nanoparticle image. A 20 nm spatial resolution of detecting nanoparticle position using defocusing image with spherical aberration was verified, and from nanoparticle motion, profile of pressure-driven flow in a 400 nm nanochannel was successfully obtained. This method can be used for single molecule tracking with bright signal intensity, and will contribute to understanding of nanoscale molecular behavior and its relationship with continuum fluid.