Water-Catalyzed Nanofabrication Strikes Gold

Hot off the frying pan may be a simple, green way to make nanomaterials. Water droplets levitating on a hot plate can catalyze formation of small amounts of nanomaterials, including gold nanoparticles and nanocoatings, without the need for other reagents, report Mady Elbahri and Ramzy Abdelaziz of Germany’s University of Kiel and colleagues (Nat. Commun. 2013, DOI: 10.1038/ncomms3400). The method exploits the Leidenfrost effect, in which water droplets on hot surfaces, such as frying pans, levitate as molecules near the surface quickly vaporize. The study showed that a drop of aqueous tetrachloroauric acid solution on a 270 °C hot plate levitated and morphed into a suspension of gold nanoparticles. Such particles are used in biomedical and other applications, but their synthesis often requires toxic reagents. The researchers also used the method to create zinc oxide and copper oxide nanoparticles and coat them on a three-dimensional object—an electron microscope specimen grid. These materials did not form at sub-Leidenfrost temperatures, highlighting the effect’s crucial role. The researchers suggest that when the hot water levitates, it becomes negatively charged, creating favorable reaction conditions. It’s not yet clear whether the method can be scaled up, they say.