Light-Induced Convective Segregation of Different Sized Microparticles

Using computational modeling, we design a facile method for sorting particles of different sizes in a fluid-filled microchamber. The microchamber is inclined at an angle with respect to the horizontal direction and contains suspended gold nanoparticles as well as the microparticles. With the application of ultraviolet light, the heat generated by illuminating the gold nanoparticles gives rise to thermal buoyancy effects, which drive the flow of the fluid in the chamber. This thermally driven, convective flow can be tailored by varying the intensity of the imposed light and the concentration of the gold nanoparticles in the solution. The competition between the drag force imposed by the fluid flows and the gravitational forces acting on the different sized particles produces the separation of the particles along the chamber's bottom, inclined wall. The separation distance between the particles can be increased by increasing the angle of inclination and the relative difference in the particle sizes. This system provides a label-free, membrane-less, and low-cost approach for sorting particles vital to a wide range of applications.