Electrodes snare microbes in key sites on silicon wafers.
Prachi Patel Predd writes in Nature: Electric currents are being used to move bacteria around silicon chips and trap them at specific locations. The technique could help to assemble nanomachines from miniature parts, and to create a new generation of biological sensors. Nanodevices are typically built by connecting tiny components. But such a delicate task is not easy. So, many researchers are exploring ways to fix components in place using the binding properties of biological molecules, notably DNA. Robert Hamers and his colleagues from University of Wisconsin-Madison propose using entire microbes instead. The cells have surface proteins that attach to certain biological molecules. Once the cells are placed at specific sites on a silicon wafer, nanoparticles tagged with these molecules can bind to the cells in those locations. This is easier than dragging the nanoparticles themselves to the right spot, because their high density makes them harder to move through fluid media than the less dense living cells. The technique gives one a way to fix components such as quantum dots or carbon nanowires at very precise locations, explains Paul Cremer, a bioanalytical chemist at Texas A&M University in College Station. “That’s potentially very exciting,” he says.
Golden rods: The researchers use Bacillus mycoides, rod-shaped bacteria that are about 5 micrometres long. They pass a solution containing the cells over a silicon wafer with gold electrodes on its surface. The charge on the electrodes captures the bacteria, which flow along the electrodes’ edges like luggage on a conveyor belt. The electrodes have tiny gaps between them. When a bacterium reaches a gap, it is trapped there by the electric field. It can be released by reducing the field between the electrodes, or permanently immobilized by increasing the voltage enough to break its cell wall.
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