Formation and capture of droplet with high volume ratio of cell to droplet

High volume ratio of cell to droplet is of great importance for the fast detection on the secreted molecule by rapidly increasing the concentration of the molecule to the detectable level. In this paper, small-volume satellite droplet that encapsulates the cell is continuously generated and captured by a T-shaped microchannel with a branching channel to achieve high volume ratio of cell to droplet. The influence of the flow rate of the continuous phase, the channel geometry and the cell concentration on the formation of the satellite droplet is systematically studied by the experiment. The results show that the smallest satellite droplet with size of ∼6.5 μm (∼0.14 pl in volume) can be generated at a low cell concentration of 16.7% and an average volume ratio of cell to droplet can be achieved as high as ∼45.9% (the relative standard deviation is 12.9%). With advantages of continuous manipulation and high volume ratio of cell to droplet, the present method could be potentially utilized as a prerequisite step for the fast detection on the secreted molecule.