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

In this paper we present a novel microfluidic chip capable of continuous mu lti-sample switching and injection for bio-analytical applications. The inn ovative device integrates two important microfluidic phenomena, including h ydrodynamic focusing and valveless flow switching inside multi-ported micro channels. The multiple samples can be pre-focused to narrow streams and can then be continuously injected into desired outlet ports. In this study, a theoretical model based on the 'flow-rate-ratio' method is first proposed t o predict the performance of the microfluidic device. Then, a simple but re liable one-mask micromachining process is developed to fabricate the pre-fo cused M x N flow switch on a quartz substrate. The multi-sample switching a nd injection is then verified experimentally with the use of microscopic vi sualization of water sheath flows and dye-containing sample flows. The expe rimental data indicate that the multi-sample flows can be hydrodynamically pre-focused and then guided into the desired outlet ports precisely based o n relative sheath and sample flow rates. The data predicted by the proposed theoretical model are highly consistent with the experimental results. It is also noted that the 'pre-focusing' function added prior to multi-sample flow switching is crucial for precise sample injection. The novel microflui dic chip has great potential for high-throughput chemical analysis, cell fu sion, fraction collection, fast sample mixing and many other applications i n the field of micro-total-analysis systems.