- Characterizing flow fields at sub-micron, or "nano," length scales is important in developing both modeling and design capabilities for MEMS and bio-NEMS devices. The new nano-PIV technique was used to measure the two components of the velocity field parallel to the channel wall within 100 nm of the wall in fully developed and steady electroosmotic flow of dilute sodium tetraborate buffer through rectangular microchannels. In all cases, the electric double layer thickness was much less than the channel height h. An initial analysis was performed using synthetic images of the errors in nPIV associated with tracer particle mismatch within an image pair due to Brownian diffusion. The experimentally determined mobilities of the particle tracers calculated from averaged nPIV data are compared with analytical predictions of the electroosmotic mobility. The mobility results appear to have a power-law dependence upon buffer concentration.