By ELLEN GOLDBAUM
Contributing Editor
Extremely hardy bacteria that contaminate computer-chip fabrication
facilities and mean nothing but trouble for chip manufacturers have
been reproduced under controlled conditions by UB researchers who believe
they could be the basis for potentially powerful biophotonic materials.
The research, presented recently at the First International Conference
on Semiconductor Photochemistry at the University of Strathclyde in
Glasgow, Scotland, demonstrates the researchers' success in deliberately
producing these microbes encased in semiconductor prisms, an important
first step toward exploiting these invaders for biophotonic applications.
It also describes the finding that the bacteria make sufficiently
close contact with the semiconductor crystals in which they are encased
so that electrons could be passed easily between them, forming the basis
of a transistor made partly out of biological materials.
The work could lead to development of a biophotonic switch, a biologically
based switch with the potential to harness the power of light and turn
it into electricity, explained Robert Baier, professor of oral diagnostic
sciences, director of the National Science Foundation-funded Industry-University
Cooperative Research Center on Biosurfaces at UB and principal investigator.
Last year, Baier and his collaborators at the University of Arizona
and at Queens University in Belfast, Ireland, made the discovery that
Pseudomonas syzgii, which find their way into the semiconductor
manufacturing process through ultrapure water, cannot be destroyeddespite
the best efforts to do sobecause they becomes embedded in nearly perfect
layers of crystals that grow on top of silicon and germanium.
"These are bacteria that live in ultrapure water," said Baier. "Fabricators
treat the water with everything ranging from ozone to ultraviolet light
in an effort to keep these bacteria out, but still they get in and in
this very hostile environment, they adapt."
According to Baier, the bacteria chew away a little of the material
of the semiconductor material and then use it to build a tiny "house"
around themselves. In their experiments, the UB researchers could produce
these protective shells in sizes ranging from 5 micrometers to 100 micrometers,
which is about the width of a human hair.
That shell, which protects the microbes from the harsh environment
outside, actually is a new transistor because electrons can flow across
its surface, said Baier, while the presence of the bacteria means that
there now is a variable negative charge to boost or limit that electron
flow.
Since some bacteria are so sensitive to light, current flowing inside
the tiny crystal of germanium or silicon might be controlled by the
pigments in a single cell of the primitive bacteria, making it capable
of amplifying an electron signal the way an ordinary transistor amplifies
electrical current.
"Everything that lives on earth's surface is essentially a parasite,
feeding off photonic processes," said Baier. "What we are doing here,
hopefully, is finding a more effective way to harness the power of light."
The current limitation in the field of photonics is that light is
a very hard thing to grab onto, Baier said.
"Light is so elusive, but some biological organisms are so amazingly
sensitive to light that once you shine light on them, they may have
enough energy to function as biophotonic circuits," he continued.
Baier presented data from laser confocal microscopy and atomic force
microscopy experiments conducted at the UB Institute for Lasers, Photonics
and Biophotonics that demonstrated that these bacteria are in sufficiently
close contact with the shell they build around themselves that electrons
can be passedthe prerequisite for any material to function as a semiconductor.
"We have demonstrated that the skin of the bug comes right up to the
edge of the semiconductor crystal," said Baier. "This is a true intimacy
of contact, where these organisms seem to have uniquely nucleated inside
of the crystals."
Baier said the researchers were lucky to have found that the microbes
did, in fact, self-fluoresce under laser illumination.
That property allowed the scientists to make observations without
having to add extraneous materials to the microbes in order to make
them fluoresce.
"It also increases the prospects that these bacteria are electronically
Ôrich' and will be able to perform important functions," he said.
The next step for the researchers is to attach micro-wires to the
new "biochip" and monitor how electron-hole flow is modulated by light-stimulated
bacterial activity, work that again will involve the Institute for Lasers,
Photonics and Biophotonics.
"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,"
he said.
"The question we originally set out to answer, with support from the
NSF, was 'how can these bacteria live in ultrapure systems and contaminate
these semiconductors'?" Baier said. "We were asking the question to
figure out how to eliminate these bacteria, but it turned out we discovered
something that could be the beginning of an entirely new field."
The work was co-authored by Robert L. Forsberg of UB and Jan Sjogren
of the University of Arizona.