Microfluidic high-throughput encapsulation and hydrodynamic self-sorting of single cells

TLDR

A purely hydrodynamic approach is developed to encapsulate single cells into picoliter droplets and to self‑sort these droplets in a high‑throughput manner. The method employs a flow‑focusing geometry that triggers a Rayleigh–Plateau instability, coupled with lateral drift of deformable objects in shear flow and steric dispersion in compressional flow, enabling continuous on‑flight encapsulation and sorting at rates up to 160 cells per second and compatible with simple soft‑lithography chips. The system is robust and cost‑effective, achieving 70–80 % single‑cell encapsulation with <1 % empty droplets, and can enrich cancerous lymphocytes from whole blood by over 10,000‑fold.

Abstract

We present a purely hydrodynamic method for the high-throughput encapsulation of single cells into picoliter droplets, and spontaneous self-sorting of these droplets. Encapsulation uses a cell-triggered Rayleigh–Plateau instability in a flow-focusing geometry, and self-sorting puts to work two extra hydrodynamic mechanisms: lateral drift of deformable objects in a shear flow, and sterically driven dispersion in a compressional flow. Encapsulation and sorting are achieved on-flight in continuous flow at a rate up to 160 cells per second. The whole process is robust and cost-effective, involving no optical or electrical discrimination, active sorting, flow switching, or moving parts. Successful encapsulation and sorting of 70–80% of the injected cell population into drops containing one and only one cell, with &lt;1% contamination by empty droplets, is demonstrated. The system is also applied to the direct encapsulation and sorting of cancerous lymphocytes from a whole blood mixture, yielding individually encapsulated cancer cells with a &gt;10,000-fold enrichment as compared with the initial mix. The method can be implemented in simple “soft lithography” chips, allowing for easy downstream coupling with microfluidic cell biology or molecular biology protocols.