Laser Induced Bubbles Speed Up Lab-on-a-Chip Devices

Thanks to tiny and rapidly imploding gas bubbles, scientists of the University of Twente succeed in speeding up the fluid flow in a micro channel. Apart from that, the bubbles form a strong new way of mixing fluids within a lab-on-a-chip, without the need of complicated external components. The scientists led by dr. Claus-Dieter Ohl of the MESA+ Institute for Nanotechnology present their results in a June 2007 edition of Physical Review Letters.

‘Controlled cavitation’ is the basis for the new technique: using a laser, a bubble is induced in the micro channel, by local heating and low pressure. This bubble has a short life: it rapidly implodes caused by the higher pressure in the channel. This causes the fluid flow to go up to 20 meters per second. Near a channel wall, the effect is spectacular. There a jet is formed, together with to tiny bubbles around which a strong circular flow forms. This is an ideal way of mixing fluids.

Simple and fast
In micro fluidics, other physical laws become dominant over those valid for large-scale systems. Viscous forces take over, and this implies that often additional components –for example micromechanical devices- are necessary for mixing and speeding up the flow. Those components , in turn, require additional electronics and wiring and can make a lab-on-a-chip fairly complicated. The laser can be directed to any spot where mixing or acceleration is needed, this is even made easier by the fact that micro fluidic systems are often transparent. The MESA+ scientists therefore see their new approach as a powerful new tool in micro fluidics and lab-on-a-chip systems.

The special project website http://stilton.tnw.utwente.nl/people/ohl/controlled_cavitation.html shows some videos about the application of the bubbles in various geometries.

The research has been done in a multidisciplinary team of scientists from the MESA+ Institute for Nanotechnology of the University of Twente: from the Physics of Fluids group of prof. Detlef Lohse and the BIOS Lab-on-a-chip group of prof. Albert van den Berg. They cooperated with Shimadzu Europe.