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

In this paper, we present an investigation of a microfluidic chip capable of continuous sample switching and injection for bio-analytical applications. The novel device integrates two important microfluidic phenomena, including hydrodynamic focusing and valveless flow switching inside multi-ported microchannels. In this study, a simple theoretical model based on the 'flow-rate-ratio' method is first proposed to predict the performance of the device. Based on these data, a pre-focused 1 × N flow switch is designed and fabricated using micromachining techniques. A novel micromachining technique is demonstrated which combines quartz template fabrication and replication of microstructures on polymethylmethacrylate (PMMA) substrates for mass production of microfluidic devices. Three-dimensional templates with an inverse image of microfluidic channels are fabricated on quartz substrates and then used to imprint microstructures onto PMMA substrates using hot embossing methods. Finally, the flow switching is verified experimentally with the use of microscopic visualization of water sheath flows and a dye-containing sample flow. The experimental data indicate that the sample flow could be hydrodynamically pre-focused to a narrow stream and then guided into a desired outlet port based on relative sheath and sample flow rates. It also shows that the added 'pre-focusing' function prior to the flow switching is crucial for precise sample injection. The microfluidic chip could be applied in the fields of bio/chemical analysis.