By making colonies of bacteria periodically fluoresce, a team of researchers at the University of California San Diego may have hit upon a significant breakthrough in the field of bioluminescence. Though the development has the potential to unplug the neon sign, it may also usher in a new generation of hazard-detecting biological sensors.

The periodic bioluminescence is brought about by applying a fluorescent protein to the bacteria, linked to their biological clocks. But to synchronize the millions of bacteria required for a potentially useful application poses additional problems, and it is here that this latest research has gained ground.

That bacteria are able to communicate and coordinate with each other via a mechanism known as quorum sensing is well-documented. However, the response is too delayed to immediately synchronize illumination on this scale. Instead, the team of biologists and bioengineers discovered that gas emitted by a bacterial colony can be shared between colonies to achieve synchronization.

A single fluorescing bacterial colony makes up what the research team calls a biopixel, hundreds or thousands of which can be incorporated into a microfluidic chip. Within this chip, gases emitted by each biopixel are shared, and the overall periodic fluorescence synchronized. Chips have been built incorporating between 500 and 13,000 biopixels, from which flashing signs could conceivably be constructed rather like traditional neon signs. The largest chips are roughly the size of a paper clip.

There are other possible applications, thanks to the additional characteristics of bacteria. The research team showed that the theory could be applied to create biological sensors, since bacteria react to the presence of numerous toxins and organisms. Specifically, the team were able to successfully slow the rate at which the bacteria fluoresced by exposing them to arsenic.

"These kinds of living sensors are intriguing as they can serve to continuously monitor a given sample over long periods of time, whereas most detection kits are used for a one-time measurement," explained Jeff Hasty of UC San Diego, who lead the research. "Because the bacteria respond in different ways to different concentrations by varying the frequency of their blinking pattern, they can provide a continual update on how dangerous a toxin or pathogen is at any one time."

Hasty believes that a hand-held sensor to detect toxins or harmful organisms may be seen within five years. The embedded video below from UC San Diego shows fluorescing bacterial biopixels in sync.

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