Pressure-Driven Microfluidic Device for Droplet Formation with Minimized Dead Volume

抄録

This paper reports a microfluidic droplet formation device suitable for manipulating small amounts of samples using a pressure-driven liquid-delivery system. In this system, a small volume (less than 100 µL) of the sample solution was loaded into the liquid reservoir and delivered by nitrogen gas pressure instead of mechanical pumps. Water-in-oil (W/O) droplets were then formed in the microchannels with a minimized dead volume. We fabricated a disposable microfluidic device from a silicone elastomer, using photolithography and replica molding. The microfluidic device consisted of microchannels, a junction, and a step structure for the preparation of W/O droplets via the step emulsification mechanism that we reported previously. The flow rates of the dispersed and continuous phases were both reasonably well controlled by the applied pressure. We observed that the droplet formation behavior depended on the applied pressure; small droplets, of average diameter 74–80 µm, were prepared at applied pressures lower than 20 kPa, and large droplets, of average diameter more than 400 µm, were prepared at applied pressures higher than 20 kPa. The prepared droplets had a narrow size distribution, with coefficients of variation less than 4.1% under all experimental conditions. The droplet formation behavior, including its change above 20 kPa, was similar to that observed in our previous study using mechanical pumps. The results indicate that the performance of the pressure-driven microfluidic droplet formation technique was as well controlled as that using mechanical pumps. The pressure-driven microfluidic droplet formation technique reported in this study, which achieves minimum sample loss and disposability, is expected to have applications to droplet formation, and encapsulation and compartmentalization of valuable biological samples.