A microflow velocity measurement system based on optical tweezers: A comparison using particle tracking velocimetry

Lab-on-a-chip devices have become useful to study substances not available in macrometric amounts. To manipulate the substances under study, ways to induce flow within such devices have been developed and, at the same time, methods to measure flow velocity have been required for the micro-scale. Several velocimetry techniques have been adapted from the macro to the micro scale, such as micro-particle image velocimetry (micro-PIV) and micro-particle tracking velocimetry (micro-PTV). However, the use of a system based on optical tweezers (OT) to measure flow velocity, specifically in microenvironments is possible. With the aim of highlighting the capabilities of an OT-based velocimetry system (OTV), we report the use of such system to measure flow velocity in a rectangular microchannel. Velocity measurements at different depths from the channel wall were carried out. As expected, an increment of the flow velocity with depth was observed. The results obtained with the OTV system were compared with measurements carried out by means of a time-averaged particle tracking velocimetry (TA-PTV). We found that both techniques provided similar results, therefore we demonstrate the capability of the OTV system to measure flow velocities in micrometric scale. The advantages of the OTV system are: (1) better space resolution, (2) minimization of the Brownian motion influence in the measurements and (3) the possibility to have submicrometric spatial resolutions without the employment of high particle concentrations, special data processing, or complex illumination systems like in other microvelocimetry techniques.