Electronic Design

Don't Sterilize Yet! That Bacteria May Be A Good Transistor

Most chip makers work very hard to keep bacteria from contaminating their fabrication facilities. But a group of SUNY at Buffalo researchers want to keep the little critters around. These microscopic menaces could be the key to powerful new biophotonic materials. The researchers have successfully reproduced microbes encased in semiconductor prisms, a first step toward exploiting them for biophotonic applications.

A bacteria known as pseudomonas syzgii finds its way into the semiconductor manufacturing process through ultrapure water. Fabricators have tried everything from ozone to ultraviolet light in an attempt to stop it and prevent contamination, but none of their efforts have completely worked. That's because pseudomonas syzgii becomes embedded in nearly perfect layers of crystals that grow on top of silicon and germanium.

Specifically, the bacteria chew away some of the semiconductor material and then use it to build a tiny "house" around themselves. This shell not only protects the microbes, it also acts as a raw transistor. Electrons can flow across its surface. Meanwhile, with the presence of the bacteria itself, there is a variable negative charge to boost or limit that electron flow.

Some bacteria are so sensitive to light, the current flowing inside the tiny crystal of germanium or silicon might be controlled by the pigments in a single cell of the bacteria. The organism, then, would be able to amplify an electron signal the way an ordinary transistor amplifies electrical current. Data from laser confocal microscopy and atomic force microscopy demonstrated that the bacteria reside close enough to the shell for electrons to be passed, a prerequisite for semiconductor function.

Fortunately, the microbes self-fluoresce under laser illumination. The researchers could then observe them without adding extraneous materials. It also signifies that the bacteria may be electronically "rich" and able to perform important functions. During the course of the experiment, the researchers produced protective shells ranging in size from 5 to 100 µm, or about the width of a human hair.

Next, the researchers have to attach microwires to the new "biochip" and monitor how electron-hole flow is modulated by light-stimulated bacterial activity. Robert Baier, professor of oral diagnostic sciences at SUNY at Buffalo, says, "We don't know how to manipulate light, but with this kind of biochip, we hope that we will be able to find a more efficient way to convert light waves to electricity, and we do know how to manipulate electricity."

For more information about this research, go to www.buffalo.edu.

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