“We found that selenium spheres are different - in terms of structural organization as well as optical absorption properties - depending on the pathway by which they were produced, e.g. bacterial species, environment,” said Pulickel Ajayan of Rensselaer. “What is interesting is the fact that new structures and forms (particularly nanoscale materials) can be produced by the bacterial route. One may be able to produce structures that are difficult by chemical synthetic routes.”
Ajayan, Ronald Oremland at the US Geological Survey and colleagues studied selenium produced by the anaerobic bacteria Sulfurospirillum barnesii, Bacillus selenitireducens and Selenihalanaerobacter shriftii. The bacteria respire selenium oxyanions, creating elemental selenium in the form of nanospheres with a diameter of 200 to 400 nm.
The researchers also examined selenium nanospheres formed by two chemical routes - the oxidation of gaseous hydrogen selenide (H2Se) and the reduction of selenite with ascorbic acid. The selenium made from hydrogen selenide ranged in diameter from 200 to 800 nm, while the material formed by selenite reduction was very variable in size, containing particles as small as 10 nm across and 50 micron aggregations of particles.
All the materials had different UV-visible absorption spectra and Raman spectra, indicating that they had dissimilar structures.
“We are only at the materials discovery stage and applications of these structures are not fully considered,” said Ajayan. “In the future we would certainly like to look at similar structures of other elements and perhaps tune these structures into other forms and morphologies.”
The researchers reported their work in Applied and Environmental Microbiology.