Ultraviolet Light Controls Fluid Flow

A new, simple, low-cost method for controlling particle motion and assembly within liquids using ultraviolet light could improve drug delivery, chemical sensors, and fluid pumps. The method encourages particles, ranging from plastic microbeads to bacterial spores to pollutants, to assemble and organize in a specific location within a liquid and, if desired, to move to new locations.

Many applications such as sensors, drug delivery, and nanotechnology necessitate precise fluid flow control. The new method allows researchers to gather particles in one location to perform a proper function, then move them to another location to perform the function again.

The researchers added a small amount of titanium dioxide or gold nanoparticles to a liquid, such as water, that also contains larger particles of interest, such as pollutants or beads carrying a payload. They heated the tiny metal nanoparticles by shining ultraviolet light at a specific liquid point and transferring the heat to the fluid. The warmer liquid then rises at the point of light, similar to how warm air rises in a cold room, and cooler water rushes in to fill the space left by the warm water, bringing the larger particles with it. The process rate is affected by the intensity of the light or the amount of titanium dioxide or gold particles present.

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