Optoelectronic technique controls fluid flow in microdevices


Technical Insights' Inside R&D

Palo Alto, Calif.-- February 3, 2004--Improvements in optoelectronics miniaturization underpin a novel technique that uses light to control the flow of nano-size volumes of fluids over solid surfaces. This has set the stage for an advanced line of optically driven microfluidic devices capable of transferring small droplets of fluids in a reprogrammable way.

This innovative optical technique uses lasers, or optical systems comparable to those in liquid crystal display (LCD) projectors, to generate complex patterns of differing light concentrations on a flat substrate.

Varying amounts of light are then absorbed by the substrate. The absorbed light, in turn, generates differing levels of heat, producing a pattern of thermal gradients on the substrate. The heat alters the surface tension, causing miniscule amounts of fluid to migrate from cooler to warmer areas through thermocapillary action.

Microfluidic devices based on this optoelectronic technique represent an advance over existing channel and pipe-based alternatives.

"Such devices preclude the need to etch detailed architectures of pipes or channels into the substrate," says Technical Insights Research Analyst Charles Joslin. "Other advantages include quick change and fast flow rates. Moreover, the substrate, without channels, can be easily cleaned between uses, avoiding contamination."

"This technique could support a miniaturized lab-on-a-chip for genetic or biochemical testing in the field," explains Joslin. "Such an easily reconfigurable system would be able to transport, merge, mix, and split off streams of fluid flowing across a flat surface."

These optically driven, dynamically reconfigurable microfluidic devices are still in development. Existing technical challenges include controlling evaporation, developing interfaces to get the tiny volumes of liquid onto the surface, and choosing the right combination of substrate and heat sink to provide distinct temperature gradient patterns without overheating the fluids.

Source: Eurekalert & others

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