Moving water on the nanoscale with the help of a hand-held magnet
At the nanoscale, water molecules stick to the micro-channels they travel along and the pumps pushing them round. The chemists, led by Michael Sailor, turned to silicon particles termed ’smart dust’, with a nanostructure that can be engineered ’to give them rudimentary sensing, data processing, communication and homing capabilities,’ says Sailor.
Smart dust particles are one-dimensional photonic crystals created by etching two different reflective surfaces, known as rugate filters, into a silicon wafer, which is then fractured into micrometre-sized particles. These are subjected to thermal oxidation, which turns one of the rugate filters hydrophilic while the other remains hydrophobic. Thus, the particles spontaneously align at an organic liquid-water interface.
Sailor’s team incorporated superparamagnetic nanoparticles of Fe3O4 during the oxidation step of smart dust production, trapping the magnetite nanoparticles within the oxide matrix. When these particles are added to water in an organic phase, they surround the water droplets, which can then be moved by hand-held magnets.
The chemists found that this technique could enable specific chemical reactions at the nanoscale by taking two smart dust-encased water droplets, one containing potassium iodide and the other silver nitrate, and ramming them together. This produced a single droplet containing the reaction product silver iodide.
According to the researchers, the technique could be used to carry out similar reactions with a whole range of inorganic and organic molecules, including DNA and proteins.
J R Dorvee et al., Nature Materials (DOI: 10.1038/nmat1253)