Micromachined pre-focused M×N flow switches for continuous multi-sample injection

Abstract

In this paper we present a novel microfluidic chip capableof continuous multi-sample switching and injection for bio-analyticalapplications. The innovative device integrates two importantmicrofluidic phenomena, including hydrodynamic focusing and valvelessflow switching inside multi-ported microchannels. The multiplesamples can be pre-focused to narrow streams and can then becontinuously injected into desired outlet ports. In this study, atheoretical model based on the `flow-rate-ratio' method is firstproposed to predict the performance of the microfluidic device. Then,a simple but reliable one-mask micromachining process is developed tofabricate the pre-focused M×N flow switch on a quartzsubstrate. The multi-sample switching and injection is then verifiedexperimentally with the use of microscopic visualization of watersheath flows and dye-containing sample flows. The experimental dataindicate that the multi-sample flows can be hydrodynamicallypre-focused and then guided into the desired outlet ports preciselybased on relative sheath and sample flow rates. The data predicted bythe proposed theoretical model are highly consistent with theexperimental results. It is also noted that the `pre-focusing'function added prior to multi-sample flow switching is crucial forprecise sample injection. The novel microfluidic chip has greatpotential for high-throughput chemical analysis, cell fusion,fraction collection, fast sample mixing and many other applicationsin the field of micro-total-analysis systems.