Magnetic Nanopropellers On The Move

Inspired by the corkscrew motion of bacterial flagella, scientists working at Harvard University's Rowland Institute have created a legion of nanostructured swimmers that can be propelled wirelessly through water via a magnetic field (Nano Lett., DOI: 10.1021/nl900186w). The tiny propellers are the first fully controlled artificial swimmers that can be navigated with micrometer-level precision, according to their inventors, Peer Fischer and Ambarish Ghosh. The mobile structures' small size makes them attractive agents for carrying chemicals or conducting rheological measurements. At just 200–300 nm wide and 1–2 μm long, they are also considerably smaller than previously reported corkscrew swimmers, the smallest of which is about 30 μm long. Fischer and Ghosh fashion the swimmers out of glass so that they are easy to chemically functionalize. The researchers cover a silicon wafer with a monolayer of glass beads and then grow the helices from silica vapor via glancing-angle deposition. A partial cobalt coating is added to make the swimmers magnetic. Fischer and Ghosh hope to someday see such tiny artificial swimmers used in biomedical applications.