Microfluidic sorting system based on optical force switching

We report a versatile, and automatic method for sorting cells and particles in a three dimensional polydimethylsiloxane (PDMS) structure consisting of two cross-microchannels. As microspheres or yeast cells are fed continuously into a lower channel, a line shaped focused laser beam is applied (perpendicular to the direction of flow) at the crossing junction of the two channels. The scattering force of the laser beam was employed to push microparticles matching specific criteria upwards from one channel to another. The force depends on the intrinsic properties of the particles such as their refractive index and size, as well as the laser power and the fluid flow speed. The combination of these parameters gives a tunable selection criterion for the effective and efficient sorting of the particles. The introduction of the cylindrical lens into the optical train allows for simultaneous manipulation of multiple particles which has significantly increased the efficiency and throughput of the sorting. A high aspect ratio microchannel (A.R.=1.6) was found to enhance the sorting performance of the device. By careful control of the microparticle flow rate, near 100% sorting efficiency was achieved.