Characterization of pressure-driven water flows in nanofluidic channels by mass flowmetry.

With developments in analytical devices promoted by nanofluidics, estimation of the flow rate in a nanochannel has become important to calculate volumes of samples and reagents in chemical processing. However, measurement of the flow rate in nanospaces remains challenging. In the present study, a mass flowmetry system was developed, and the flow rate of water by pressure-driven flow in a fused-silica nanochannel was successfully measured in picoliters per second. We revealed that the water flow rate is dependent on the viscosity significantly increased in a square nanochannel with 10 nm width and depth (3.6 times higher than the bulk viscosity for a representative channel size of 190 nm) and slightly increased in a plate nanochannel with micrometer-scale width and 10 nm depth (1.3 times higher for that of 234 nm), because of dominant surface effects. The developed method and results obtained will greatly contribute to nanofluidics and other related fields.