Micromachined pre-focused 1 x N flow switches for continuous sample injection

In this paper, we present an investigation of a microfluidic chip capable o f continuous sample switching and injection for bio-analytical applications . The novel device integrates two important microfluidic phenomena, includi ng hydrodynamic focusing and valveless flow switching inside multi-ported m icrochannels. In this study, a simple theoretical model based on the 'flow- rate-ratio' method is first proposed to predict the performance of the devi ce. Based on these data, a pre-focused 1 x N flow switch is designed and fa bricated using micromachining techniques. A novel micromachining technique is demonstrated which combines quartz template fabrication and replication of microstructures on polymethylmethaerylate (PMMA) substrates for mass pro duction of microfluidic devices. Three-dimensional templates with an invers e image of microfluidic channels are fabricated on quartz substrates and th en used to imprint microstructures onto PMMA substrates using hot embossing methods. Finally, the flow switching is verified experimentally with the u se of microscopic visualization of water sheath flows and a dye-containing sample flow. The experimental data indicate that the sample flow could be h ydrodynamically pre-focused to a narrow stream and then guided into a desir ed outlet port based on relative sheath and sample flow rates. It also show s that the added. 'pre-focusing' function prior to the flow switching, is c rucial for precise sample injection. The microfluidic chip could be applied in the fields of bio/chemical analysis.