Magnets propel nano sized screws

Two researchers at Harvard University, one of them British educated, have developed tiny glass screws that can be propelled through fluids using a rotating magnetic field.

Dr Ambarish Ghosh and Dr Peer Fischer, researchers at the Rowland Institute at Harvard University, have found a way to grow 1billion silica glass screws, which they call propellers, on every square centimetre of a silicon substrate. The screws, or propellers, are around 200 to 300nm across, and about one to two microns long. They are coated on one side with vapour deposited cobalt and magnetised in such a way that their magnetic moment is perpendicular to their long axis.

A tri-axial Helmholtz coil is used to generate a magnetic field of about 50Gauss, rotating at frequencies of up to 170Hz, with full directional control in all three dimensions. This causes the devices to screw their way through fluid at a speed of up to around 40 microns/s.

The intention is to use them to carry chemicals, such as pharmaceuticals to be accurately delivered within the human body, push loads and act as local probes in rheological measurements.

Author
Tom Shelley

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