Puny pump, powerful prospects

The electro-osmotic pump transports fluid through the central axis between the greenish silver electrodes. Bypasses are needed to prevent blockage by entrapped air bubbles (Photo: Friedjof Heuck)

The micropipette can deliver fog droplets of liquid to molecule-sized targets. Pharmaceutical labs are following the developments with great interest.

“It’s not a world record, but it’s definitely one of the smallest pumps ever made,” says Dr Friedjof Heuck, of the microscopic pump he developed at Dimes. German-born Heuck followed his professor, Urs Staufer, from Switzerland to Delft three years ago. Prof. Staufer (Mechanical, Maritime and Materials Engineering) wanted to extend the scanning force microscope (a device that scans surfaces with resolution in the nanometre range) with a micropipette, including a pump and electrodes. After three years, Dr Heuck has succeeded in constructing an electric pump that measures only 40 microns across (one half of a hair). The active part is even thinner, about a tenth of a hair, and pumps 35 picolitre (a millionth of a millionth litre) per second – it would need nine centuries to pump a litre.

The electro-osmotic pumping process only works on the microscopic scale. From the glass surface, hydrogen ions diffuse into the solution, leaving a negatively charged glass surface behind. Consequently, positive ions stick to the glass. Applying an electric field between two electrodes on opposite sides of the glass channel will pull this carpet of charges along the sidewall, and with it the water column on top. “It only works at small diameters,” Dr Heuck explains, “and if you make it too small then friction will block it.”
What Dr Heuck and Prof Staufer envision is using microfluidic systems to administer drugs or biological messengers onto a living cell and see how it reacts. Find the right substance and you will see the cell pore opening. The puny pump could also be integrated in lab-on-a-chip devices. A future doctor won’t need to send your sample to the lab; he’ll just use a disposable one instead.

Dr Friedjof Heuck successfully defended his thesis, Developing and Analysing sub-10 µm Fluidic Systems with integrated Electrodes for Pumping and Sensing in Nanotechnology Applications, on 28 October 2010. His PhD supervisor was Professor Urs Staufer.

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