By interfacing bacteria to silicon chips, researchers have created
a device that can sense almost anything.
by Karen Miller
Like a canary in a
mine, a microbe can often sense environmental dangers before a human
can. It's easy to see a canary's reaction. But how can you can you
tell what a microbe's feeling? How can you coax a microbe to communicate?
One way is to interface
it to a silicon chip.
University of Tennessee
microbiologist Gary Sayler and his colleagues have developed a device
that uses chips to collect signals from specially altered bacteria.
The researchers have already used these devices, known as BBICs,
or Bioluminescent Bioreporter Integrated Circuits, to track pollution
on earth. Now, with the support of NASA's Office of Biological and
Physical Research, they're designing a version for spaceships.
Sayler's group, which
includes Tennessee researchers Steve Ripp, Syed Islam and Ben Blalock,
as well as collaborators at JPL and the Kennedy Space Center, has
bio engineered microbes that glow blue-green in the presence of
contaminants. Then they joined those bacteria to microluminometers
- chips designed to measure the light.
What BBICs offer,
explains Sayler, is a low-cost, low-energy way to detect pollutants.
They're tiny: each BBIC is about 2 mm by 2 mm, and the entire device,
including its power source, will probably be about the size of a
matchbox, and they monitor their surroundings continuously.
Glowing colonies of microbes
NASA is interested
in sensing contaminants because spaceships are tightly sealed. Unseen
fumes from scientific experiments or toxins produced by molds and
other biofilms can accumulate and pose a hazard to astronauts. BBICs
can be crafted to sense almost anything: ammonia, cadmium, chromate,
cobalt, copper, proteins, lead, mercury, PCBs, ultrasound, ultraviolet
radiation, zinc - the list goes on and on.
The system is surprisingly
rugged. Microbes thrive in a wide range of environments, so it's
possible to design BBICs that can survive in extreme or highly contaminated
surroundings. "They can actually do their job sitting in things
such as jet fuel-water mixtures," marvels Sayler.
Although the microbes
can protect themselves from toxins, they still have a variety of
needs - food, for example. Keeping them alive, Sayler says, "is a
significant portion of the work."
One problem is that
microbes must be immobilized so that they remain right next to the
chip. The challenge, says Sayler, is trying to figure out how to
immobilize the microbes in such a way that they survive as long
The researchers are testing various substances that will keep the
microbes in place. Something with good optical transparency is critical,
of course, so that if the microbes light up, the chip can perceive
that. The immobilant has to be porous, so that any contamination
can flow in, and reach the microbes. It has to contain nutrients
for the microbes to feed on. It has to allow the microbe enough,
but not too much, room. "We're basically trying to feed the immobilized
organisms in the matrix without them growing. We really don't want
them to grow very much, if at all. If they grow, it changes the
total amount of cells in the system, and it confounds the issue
of how much light corresponds to how much contaminant."
integrated circuit microluminometer. Actual size is 2
mm by 2 mm.
(There needs to be
about a few thousand microbes per chip, says Sayler, in order to
generate enough light. That's not as many as it seems, though -
it's only about enough to cover the tip of a pin.)
Sayler hopes to develop
gels in which the microbes can be kept functional for several months.
The sensors would probably be attached to the spaceship walls, continuously
monitoring the ship's atmosphere. They'd monitor themselves, too,
to make sure that the microbes were still viable. "We can electrically
induce cells to make light, so we can pulse the system every once
in a while to see if the organisms are still physiologically active."
The basic architecture of a BBIC.
"After, say, six months,
the chip would send a signal that says, 'oops, time to replace your
bug sensor.' An astronaut would go and get a freeze-dried package
of seed microbes, add a little moisture, and stick it in the sensor."
Nothing more has to be done until the next time the signal goes
off, six months later. It's a low maintenance system.
These BBICs are useful
on Earth, too. They can detect formaldehyde emitted by pressed wood
furniture or hard-to-detect molds often implicated in sick building
syndrome. "If this device works as planned, it could turn out to
be a very inexpensive kind of monitoring system," says Sayler. "You
could go to your corner drugstore, buy one of these, take it home
and stick it up on your wall. It could tell you whether your carpets
are degassing, or whether you've got problems like black mould."
Advanced BBICs could
serve as bio terrorism monitors for Homeland Security, as a means
to detect DNA radiation-damage in astronauts, or as a diagnostic
tool for doctors. An example: Sayler envisions BBICs as part of
a treatment program for diabetics. An implantable BBIC equipped
with an on-chip radio transmitter could monitor blood glucose levels
and communicate with a remote insulin delivery system. Such devices
could also scan body-fluids for certain proteins that signal tumours
- in other words, an early warning system for cancer.
Much more research
needs to be done before these ideas become reality. Making BBICs
work on spaceships is a good place to start.