Inertial microfluidics for sheath-less high-throughput flow cytometry

Flow cytometer is a powerful single cell analysis tool that allows multi-parametric study of suspended cells. Most commercial flow cytometers available today are bulky, expensive instruments requiring high maintenance costs and specially trained personnel for operation. Hence, there is a need to develop a low cost, portable alternative that will aid in making this powerful research tool more accessible. In this paper we describe a sheath-less , on-chip flow cytometry system based on the principle of Dean coupled inertial microfluidics. The design takes advantage of the Dean drag and inertial lift forces acting on particles flowing through a spiral microchannel to focus them in 3-D at a single position across the microchannel cross-section. Unlike the previously reported micro-flow cytometers, the developed system relies entirely on the microchannel geometry for particle focusing, eliminating the need for complex microchannel designs and additional microfluidic plumbing associated with sheath-based techniques. In this work, a 10-loop spiral microchannel 100 µm wide and 50 µm high was used to focus 6 µm particles in 3-D. The focused particle stream was detected with a laser induced fluorescence (LIF) setup. The microfluidic system was shown to have a high throughput of 2,100 particles/sec. Finally, the viability of the developed technique for cell counting was demonstrated using SH-SY5Y neuroblastoma cells. The passive focusing principle and the planar nature of the described design will permit easy integration with existing lab-on-a-chip (LOC) systems.