Ironically, the places where drinking water needs to be checked most for germs are the least likely to have laboratories that can perform the analysis. A new “lensless” device that uses light to instantly detect harmful microorganisms could help.
Typically, to test drinking water for bacteria, a sample of that water must be cultured in a Petri dish for 12 to 48 hours. This process is not only time-consuming, but must be performed by trained personnel in a laboratory. In developing countries, such laboratories may be few and far between.
An alternative involves using a device known as a fluorometer. It exposes a water sample to ultraviolet light, which causes proteins found in harmful bacteria to fluoresce. By detecting and measuring this fluorescence, it is possible to determine how much bacteria, if any, are present in the sample.
In most fluorometers, one pair of lenses focuses light onto the sample, while the other pair focuses the resulting fluorescence onto an integrated sensor. Because these lenses must be precisely manufactured and precisely positioned, they add to the cost, complexity, and weight of the fluorometer. This makes the instruments prohibitively expensive and impractical for many impoverished areas.
To address this issue, Dr. Ashim Dhakal and colleagues at Nepal's Phutung Research Institute developed a fluorometer that does not use a fluorometer. to have any lens. Instead, it uses a 1 x 1 mm ultraviolet LED to excite bacterial proteins and a 2.4 x 2.4 mm photodiode to measure the resulting fluorescent signal.
Rijan Maharjan, Ashim Dhakal, Phutung Research Institute
The experimental apparatus is not only simpler and cheaper than a typical lens fluorometer, but also more sensitive. This is mainly because no space is left for focusing the light or the lenses themselves, meaning that the light source, sample and photodiode can be as close together as possible, producing a much stronger signal.
In laboratory tests, the device was able to detect bacterial proteins in water at levels of less than one part per billion, which meets the World Health Organization's standards for detecting fecal contamination in drinking water.
Dhakal and his colleagues are currently working on a small, handheld version of the fluorometer that can be placed in containers of water to take instant measurements.
“In developing countries, unsafe water supplies cause more than a million deaths each year,” he says. “We hope that our work will facilitate the development of simpler and more cost-effective yet highly efficient detection paradigms for drinking water, saving countless lives around the world.”
An article on the research, which also involved scientists from the University of São Paulo in Brazil and the University of York in England, was recently published in the journal Optical.
Source: Optica