Usually when you hear the words X-rays and bacteria in the same sentence, the bacteria are at the receiving end of the X-ray source, being imaged, irradiated for some treatment, or simply assessed for radiation damage. You don’t expect the bacteria to be used as the actual source of the X-rays.
But in work that overturns traditional assumptions and practice, researchers used a femtosecond infrared, high-intensity laser to irradiate a glass slide coated with E. coli bacterial cells, turning the cell material into a hot, dense plasma.
Laser-driven plasmas are useful table top X-ray sources, and researchers are continuously striving to improve their brightness. One such effort, an important one, has been to create plasmas on a nanostructured surface where the nanostructure amplifies the intensity by electromagnetic local field enhancement.
In this study, the researchers theorized that natural micro and nanostructures in the bacteria can be readily used for such intensity enhancement, leading to hotter, brighter plasma. In fact, they demonstrated that the bacterial cells increased the X-ray flux by a factor of 100 in the 50 – 300 keV X-ray region.
Additionally, the scientists grew the bacterial cells in a silver chloride solution in which the silver atoms aggregated as nanoparticles inside the cell.
They could then use these bacteria spiked with nanoparticles to expand the emission another 100 times, leading to an overall enhancement of 10,000 times from the flux emitted by plain glass slides without the bacterial coating. This is the highest conversion of laser light to hard X-rays ever achieved.
The innovation could eventually result in biologically inspired plasma physics and high energy density science having multiple applications among novel particle sources, creation of extreme excited states and related areas.