A dense bed of light-sensitive bacteria has been developed as a unique kind of photographic film. Although it takes 4 hours to take a picture and only works in red light, it also delivers extremely high resolution.
The “living camera” uses light to switch on genes in a genetically modified bacterium that then cause an image-recording chemical to darken. The bacteria are tiny, allowing the sensor to deliver a resolution of 100 megapixels per square inch.
To make their novel biosensor, Chris Voigt’s team at the University of California in San Francisco, US, chose E. Coli, the food-poisoning gut bacterium. One of the reasons for that choice is that E. Coli does not normally use light – photosynthesising bacteria could have used light to prompt other, unwanted, biological processes.
The researchers used genetic engineering techniques to shuttle genes from photosynthesising blue-green algae into the cell membrane of the E. coli. One gene codes for a protein that reacts to red light. Once activated, that protein acts to shut down the action of a second gene. This switch-off turns an added indicator solution black. As a result, a monochrome image could be permanently “printed” on a dense bed of the modified E. Coli.
The living camera will never be available in the shops: Voigt’s team saw it as an exercise in advanced genetic engineering. But their success in getting an array of bacteria to respond to light could lead to the development of “nano-factories” in which minuscule amounts of substances are produced at locations precisely defined by light beams.
For instance, the gene switch need not activate a pigment, says Voigt. A different introduced gene could produce polymer-like proteins, or even precipitate a metal. “This way, the bacteria could weave a complex material,” he says.
The UCSF team are now working on expanding the colour range of their sensor, perhaps using retinol, a substance which helps the human retina to sense a wide range of colours.
As a method of nano-manufacturing, the biocamera is an “extremely exciting advance” says Harry Kroto, the Nobel prize-winning discoverer of buckminsterfullerene, or buckyballs. “I have always thought that the first major nanotechnology advances would involve some sort of chemical modification of biology.”
Source: Nature (vol 438, p 441)