The bright lights

'Lab-on-a-chip' devices are beginning to hit the market, using microscopic channels etched into silicon wafers to move tiny amounts of fluids around miniaturised analysis devices. The next stage in their development could do away with the channels altogether, relying simply on heat to move the fluids.

One system, developed by Michael Schatz and colleagues at the Georgia Institute of Technology in Atlanta, uses a completely flat substrate onto which a computer-controlled light source projects complex patterns of varying-intensity light.

The substrate absorbs the light and heats up, creating a pattern of thermal gradients matching the projected light pattern. A process known as thermocapillary action then moves nanolitre-volumes of liquid to move from cooler areas to warmer ones, powered only by the force of surface tension.

'We envisage that this could move multiple droplets or packets of fluid simultaneously, allowing arrays of drops to be moving at the same time at multiple locations,' says Schatz.

'We could avoid putting detailed architectures onto the substrate. Instead, we would take advantage of advances in optoelectronics to pattern the substrate with surface tension forces.' The system would allow the pathways for the droplets to be changed quickly - which is not possible with permanently-etched substrates - and creates faster flow rates, because there is less frictional force to be overcome.

Schatz believes that the first applications are likely to be in genetic or biological sensors, but the technique could be used to make assays, chemical studies and macro-scale processes smaller, cheaper and faster. 'The shrinking of devices using microfluidics could be as revolutionary to our daily lives as microelectronics has been,' he says.