Velocity measurement of particulate flow in microfluidic channels using single point confocal fluorescence detection

This article presents a non-invasive, optical technique for measuring parti culate flow within microfluidic channels. Confocal fluorescence detection i s used to probe single fluorescently labeled microspheres (0.93 mum diamete r) passing through a focused laser beam at a variety of flow rates (50 nL m in(-1)-8 muL min(-1)). Simple statistical methods are subsequently used to investigate the resulting fluorescence bursts and generate velocity data fo r the flowing particles. Fluid manipulation is achieved by hydrodynamically pumping fluid through microchannels (150 mum wide and 50 mum deep) structu red in a polydimethylsiloxane (PDMS) substrate. The mean fluorescence burst frequency is shown to be directly proportional to flow speed. Furthermore, the Poisson recurrence time and width of recovered autocorrelation curves is demonstrated to be inversely proportional to flow speed. The component-b ased confocal fluorescence detection system is simple and can be applied to a diversity of planar chip systems. In addition, velocity measurement only involves interrogation of the fluidic system at a single point along the f low stream, as opposed to more normal multiple-point measurements.