A gravity-actuated technique for flexible and portable microfluidic droplet manipulation

In this study, an inexpensive and robust microfluidic droplet manipulation device based on gravity-actuated technique is described. The device is mainly composed of a turntable and some disposable infusion sets. The movement of oil-phase and water-phase in the microchannel is controllable. Droplet volume of different sizes is precisely generated by controlling droplet length using the turntable. A series of essential functional units have been demonstrated including on-demand sampling, droplets generation of controllable size and controllable number, droplets fusion of different sizes and contents, even droplets-stopping. These functions can well meet the requirements of routine droplet-based microfluidic biological/chemical assays, cell research, and high content drug screening. The presented technique shows unique advantages in inexpensiveness, flexibility, and portability when compared with general droplet manipulation systems containing precision syringe pump and complicated micromechanical/pneumatic valve. Furthermore, this device can be used as a portable droplet manipulation tool in outdoor and remote areas, because it does not need electrical source and is very facile to set up in any place.