Bacterial Circuits

The integrated circuit microluminometer. Actual size is 2 mm by 2 mm.

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."

(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.