Microfluidic Accelerator

Microfluidics is the science of carrying out fluid chemical processing on a chip whose channels are typically millimeters or microns across. In such a constricted space, viscosity becomes large, and the fluid flow can slow way down, thus limiting the kind of mixing or testing that can be done. Physicists at the University of Twente in the Netherlands, however, use tiny exploding bubbles to speed things up.

The bubbles are produced by shooting laser light into the fluid. (See movie at http://stilton.tnw.utwente.nl/people/ohl/controlled_cavitation.html ) The light brings a tiny volume of fluid above its boiling temperature, causing a local bubble explosion, which accelerates the surrounding fluid along the channel, now at speeds of up to 20 m/sec, twenty times higher (and still another factor of 10 within reach) than would be the case without the bubble. (The same researchers have produced sonoluminescence in the same way.)

An extra advantage of using flexibly positioned laser light is that for transparent microfluidic chips fluid pumping can be accomplished without external connections to the chip. Besides being the first to apply such a cavitation technique for speeding up fluids on a chip, the Twente scientists are the first to achieve flow visualization at rates of a million frames per second at a size scale of 100 microns.

The leader of the Twente group, Claus-Dieter Ohl (c.d.ohl@utwente.nl, 31-53-489-5604) says that he and his colleagues are currently using the bubble acceleration technique for improving mixing in various enzyme reactions and in producing tiny pores in membranes. (Zwaan et al., Physical Review Letters, upcoming article)