Autonomous Photothermally-driven Fluid Pumping and Particle Transport and Assembly

We review the design of photothermally-driven fluid micropumps that can regulate the assembly and segregation of microparticles in solution. Externally imposed light represents particularly useful energy input since the light source (further enabled with a mask) is easily moved and thus can regulate spatially and temporally coordinated dynamics. Ultraviolet (UV) light sources are used to illuminate regions of a fluid-filled chamber that results in fluid flow throughout the chamber. The light-driven pumping occurs via three different mechanisms: thermal buoyancy, solutal buoyancy, and diffusioosmosis. These pumping mechanisms can operate simultaneously and the combination of two or more mechanisms leads to complex fluid flow patterns. This approach enables systems that allow dynamic control over the motion of immersed microparticles, including the formation and transport of reversible particle assemblies, as well as the segregation and separation of different sized particles in the fluidic chambers. Thus, one device can be used to both separate the particles and drive them to different locations for further processing. This property is particularly useful for analyzing fluids that contain multiple particulate types.