Evanescent wave-based particle tracking technique for velocity distribution in extended nanochannel

Understanding fluid flows in extended nanospace (10-1000 nm) is a fundamental issue to develop novel nanofluidic systems. The present study measured pressure driven flows in a 400 nm fused silica nanochannel by 100-300 kPa. A nanoscale particle tracking method using 64 nm fluorescent nanoparticle and the evanescent wave with total internal reflection of laser beam was developed to obtain the flow profile. The particle position in the nanochannel was determined from the fluorescent intensity, which is proportional to the evanescent wave intensity decaying exponentially from the wall. In order to reduce an error by the Brownian diffusion of tracer nanoparticles, the time resolution of the particle tracking was reduced to 260 us. Flow velocity in the nanochannel, which is much smaller than the optical diffraction limit, was successfully obtained. This study provides basic knowledge of fluid and mass transport in nanospace.