High-throughput encapsulation and passive sorting of single cells

Traditionally, digital microfluidic methods for cell encapsulation have been based on Poisson statistics and thus required a compromise between encapsulation rate and yield. Moreover, these procedures use an active sorting method, such as flow cytometry. To overcome problems with the Poisson-based encapsulation methods, Max Chabert and Jean-Louis Viovy of the Curie Institute (France) have designed a new microfluidic device that encapsulates single cells in picoliter droplets and sorts them by passive hydrodynamic effects.

In the new apparatus, cells are focused in the center channel by two parallel oil streams; the key to self-sorting after encapsulation is that the oil streams flow at different rates. The central focusing channel is split into upper and lower channels by a y-shaped junction. The oil flow rates are tuned so that only the bigger droplets that encapsulate cells float into the upper channel, and the empty droplets stream into the lower channel.

The researchers tested the system by sorting cancerous T lymphocytes from blood, and they showed that their device can encapsulate and sort up to 160 cells/s with 99% purity. (Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 3191–3196)