Micromachined pre-focused 1×N flow switches for continuoussample injection

Abstract

In this paper, we present an investigation of a microfluidicchip capable of continuous sample switching and injection forbio-analytical applications. The novel device integrates two importantmicrofluidic phenomena, including hydrodynamic focusing and valveless flowswitching inside multi-ported microchannels. In this study, a simpletheoretical model based on the `flow-rate-ratio' method is first proposedto predict the performance of the device. Based on these data, apre-focused 1×N flow switch is designed and fabricated usingmicromachining techniques. A novel micromachining technique isdemonstrated which combines quartz template fabrication and replication ofmicrostructures on polymethylmethacrylate (PMMA) substrates for massproduction of microfluidic devices. Three-dimensional templates with aninverse image of microfluidic channels are fabricated on quartz substratesand then used to imprint microstructures onto PMMA substrates using hotembossing methods. Finally, the flow switching is verified experimentallywith the use of microscopic visualization of water sheath flows and adye-containing sample flow. The experimental data indicate that the sampleflow could be hydrodynamically pre-focused to a narrow stream and thenguided into a desired outlet port based on relative sheath and sample flowrates. It also shows that the added `pre-focusing' function prior to theflow switching is crucial for precise sample injection. The microfluidicchip could be applied in the fields of bio/chemical analysis.