Credit: © 2006 ACS

Researchers in Canada have used a common cyanobacteria found in the environment to make platinum nanoparticles. By tweaking the incubation temperature and reaction times, the microbes can form nanostructures with distinct morphologies and crystallinity.

Maggy Lengke and colleagues1 at the University of Western Ontario, Canada, reacted platinum(IV) chloride with the cyanobacteria, Plectonema boryanum. At 29 °C — the optimal bacterial growth temperature — spherical nanoparticles with diameters ranging from 30 to 300 nm were formed. Electron diffraction studies revealed them to be amorphous, and transmission electron microscope images showed that they were coated with organic material derived from the bacteria. When the reaction was repeated at slightly higher temperatures (60 and 80 °C), bead-like chains were produced in which the spherical nanoparticles were connected by the organic material. At 100 °C, chains of crystalline nanoparticles — partly covered with fine grains of recrystallized platinum metal — were observed. Further increasing the reaction temperature to 180 °C resulted in crystalline platinum nanoparticles with a dendritic or branched character.

The platinum(IV) ions are thought to enter the bacterial cell where they are then reduced, in a step-wise fashion, to Pt(II) and then Pt(0). It is proposed that organic sulphur and phosphorus are involved in the reduction and complexation of platinum(IV) chloride. Lengke’s approach offers a ‘greener’ biological alternative to the more traditional chemical methods of nanoparticle synthesis, and represents a new strategy for the development of platinum catalysts.