Acoustically driven planar microfluidics

Surface acoustic waves are used to actuate and process smallest possible amounts of fluids on the planar surface of a piezoelectric chip. Chemical modification of the chip surface is employed to create virtual wells and tubes to confine the liquids. Lithographically modulated wetting properties of the surface define a fluidic network, in analogy to the wiring of an electronic circuit. Acoustic radiation pressure exerted by the surface wave leads to internal streaming in the fluid and eventually to an actuation of small droplets along predetermined trajectories. © 2004 Elsevier Ltd. All rights reserved. The knowledge of the biochemical interior of living cells steadily increases and researchers dig deeper and deeper into the biomolecular world. Now the human genome is sequenced, scientists hope to find novel drug targets once the code is cracked. Analytical techniques such as gene expression analysis and cell assays have become standard tools, used in large scale screening for new drugs. The very same technologies are the driving force behind miniaturization of the laboratories, as parallel screening requires smallest possible amounts of samples for single experiments. Many of the precious ingredients are either very limited in availability or prohibitively expensive. In this article, we wish to report a novel way of tackling the need to scale chemical and biological laboratories down to the size of a thumbnail. We describe a technique which uses virtual beakers and channels to confine smallest possible amounts of liquids to the plane surface of a microchip, and tiny earthquakes (surface acoustic waves, SAW) on this very chip to act as electrically addressable and programmable nanopumps. The combination of the two can be viewed as a step towards the realization of a programmable microfluidic processor. E-mail address: [email protected] (A. Wixforth). 0749-6036/$ see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.spmi.2004.02.015 390 A. Wixforth / Superlattices and Microstructures 33 (2003) 389–396