Multiple flow switch using stepwise sheath flow

In this paper we present a concentration-conservative flow switch using a sheath flow. A novel concept of stepwise flow was proposed to prevent the sample dilution during flow switching. Computational fluid dynamics (CFD) simulations revealed that the stepwise flow suppressed a back flow of the sample reagent that caused the sample dilution. Based on the CFD simulation results, the prototype devices of the flow switch utilizing the stepwise flow were designed. Using fabricated devices, reduction of the sample dilution by the stepwise flow was confirmed. In order to reduce the switching time, pneumatic microvalves were integrated with the flow switch. Its characteristic of the switching time was evaluated experimentally. The switching time was about 130 ms, which was reduced to less than half compared to the case of using off-chip valves. In the case that the sample flow rate is 1 μL/min, it is expected that the flow switch will achieve fluid sampling with the accuracy of the order of nanoliters.