Organization of Particle Islands through Light‐Powered Fluid Pumping

The field of active matter holds promise for applications in particle assembly, cargo and drug delivery, and sensing. In pursuit of these capabilities, researchers have produced a suite of nanomotors, fluid pumps, and particle assembly strategies. Although promising, there are many challenges, especially for mechanisms that rely on chemical propulsion. One way to circumvent these issues is by the use of external energy sources. Herein, we propose a method of using freely suspended nanoparticles to generate fluid pumping towards desired point sources. The pumping rates are dependent on particle concentration and light intensity, making it highly controllable. Using these directed flows, we further demonstrate the ability to reversibly construct and move colloidal crystals. Lights, heat, motion! The photothermal effect has been exploited to promote fluid pumping and particle assembly using suspensions of either gold or titanium dioxide nanoparticles.