Vortices-interaction-induced microstreaming for the pump-free separation of particles.

Microfluidic techniques have emerged as promising strategies for a wide variety of synthetic or biological sorting. Unfortunately, there is still a lack of sorting with automatic and handy operation. In contrast to passively generated vortices, the thermocapillary vortices produced by temperature gradient have the advantages of flexible manipulation, stable strength, and simple integration. In this Letter, we present a device used for the pump-free separation of particles through vortices interaction without external fluidic control systems required for the majority of existing devices. Specifically, the device induces a different flow type upon the actuation of optical power, and the flow functions, such as simultaneous pumping and sorting, agree with stimulation results very well. More importantly, our developed sorting device can achieve separations by means of tunable cutoff diameter size. Therefore, this versatile device can be utilized to sort complex samples with the advantages of portability, user-friendly control, and automation.