Measurements of Nanoparticle Velocity Distribution in a Square Micrometer-Channel by Defocusing Nanoparticle Tracking Velocimetry

Understanding nanoparticle transport in confined micro/nanospaces is becoming increasingly important with recent advances in micro/nanofluidic devices for particle manipulation, chemical analysis, and biomedical applications. In this study, the three-dimensional velocity distribution of 200 nm fluorescent nanoparticles flowing through a square micrometer-channel with a width and depth of 1.5µm was measured using defocusing nanoparticle tracking velocimetry (defocusing nano-PTV). Correction methods for particle positions in both the spanwise and depthwise directions were developed to compensate for channel inclination and field curvature. Calibration experiments were conducted to determine the relationship between particle image radius and depth position. As a results, accurate three-dimensional velocity measurements were achieved, and velocity data from 5,064 nanoparticles were obtained. The measured velocity distributions agreed well with theoretical profile for pressure-driven flow in a square channel. The proposed method provides a useful tool for investigating nanoparticle transport phenomena in highly confined micro/nanofspaces and for advancing micro/nanofluidic technologies.