Pulickel Ajayan, professor of materials science and engineering at Rensselaer, and geobiologist Ronald Oremland reported that three different kinds of common bacteria "grow" the element selenium in the form of uniform nanospheres. The nanoscopic balls exhibit vastly different properties than selenium that is found as a trace mineral in topsoil.

Selenium is used in photovoltaic and photoconductive technologies. It is incorporated in many electronic and technical applications, such as semiconductors, photocopiers, and photocells.

The findings of Ajayan and Oremland were published in the journal Applied and Environmental Microbiology (an American Society of Microbiology publication) in January. A summary of the research also was featured the same month in the "Editor's Choice" section of Science magazine.

Oremland, a senior scientist at the U.S. Geological Survey in Menlo Park, Calif., and a 1968 Rensselaer biology graduate, has been studying anaerobic bacteria that respire, or "breathe," soluble salts, or "oxyanions," of toxic elements, such as selenium and arsenic. He recently discovered that some of these microbes form distinctive selenium nanoscopic balls, each of which measure 300 nanometers in diameter on the outside of their cell envelopes.

Knowing little about what kinds of properties selenium exhibits on the nanoscale level, Oremland turned to his alma mater to enlist the help of Ajayan, an internationally known nanomaterials expert.

"I was interested in finding out whether this type of selenium would be useful. As a biologist, I am not familiar with the various electrical, optical, and other properties of nanomaterials," said Oremland, the paper's lead author.

Ajayan and Seamus Curran, a postdoctoral fellow working at the Nanoscale Science and Engineering Center at Rensselaer at the time, found that the nanospheres exhibited enhanced optical and semiconducting properties. They also discovered that the nanospheres grown on each of the three bacteria studied were different from each other and fundamentally different from amorphous selenium particles formed by chemical means.

"Surprisingly, we found different bacteria produce spheres with different arrangements of the selenium atoms and hence different optical properties," says Ajayan. "Remarkably, these conditions cannot be achieved by current methods of chemical synthesis."

The research could lead to the production of nanospheres, nanowires, nanorods, and other nanostructures with precise atomic arrangements for smaller, faster semiconductors and other electronic devices.

"This is an excellent example of how Rensselaer researchers are crossing over disciplines in unique collaborations that are opening up new avenues in research and discovery," said Rensselaer Provost Bud Peterson.

Other collaborators include researchers from University of Guelph in Canada, the Naval Surface Warfare Center in Virginia, and New Mexico State University.

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