It's ironic that in places where drinking water needs to be checked for microbes the most, labs that can perform the analysis are least likely to be present. A new "lensless" device could help, as it uses light to instantly detect harmful microorganisms.
Usually, in order to check drinking water for bacteria, a sample of that water must be cultured in a Petri dish for 12 to 48 hours. Not only does this process take a long time, but it has to be performed by trained personnel in a lab. In developing nations, such labs may be few and far between.
One alternative involves utilizing a device known as a fluorometer. It exposes the water sample to ultraviolet light, which causes proteins present in any harmful bacteria to fluoresce. By detecting and measuring that fluorescence, it's possible to determine how much (if any) of the bacteria are present in the sample.
In most fluorometers, one pair of lenses focuses the light onto the sample, while another pair focuses the resulting fluorescence onto an integrated sensor. Because these lenses have to be precision-made and precisely placed, they add to the cost, complexity and weight of the fluorometer. This makes the devices too expensive and impractical for many impoverished regions.
In an effort to address that problem, Dr. Ashim Dhakal and colleagues at Nepal's Phutung Research Institute developed a fluorometer that doesn't have any lenses. Instead, it simply utilizes a 1 x 1-mm ultraviolet LED to excite the bacterial proteins, and a 2.4 x 2.4-mm photodiode to measure the resulting fluorescence signal.
Not only is the experimental device simpler and cheaper than a typical lensed fluorometer, it's also more sensitive. This is due mainly to the fact that no room has to be left for the focusing of light or for the lenses themselves, meaning that the light source, sample and photodiode can be as close to one another as possible, producing a much stronger signal.
In lab tests, the device was able to detect waterborne bacterial proteins down to 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 colleagues are now working on a small hand-held version of the fluorometer, which could simply be placed in water vessels to provide on-the-spot readings.
"In developing countries, unsafe water sources are responsible for more than one million deaths each year," he says. "We hope that our work will facilitate the development of simpler and cost-effective yet highly efficient sensing paradigms for drinking water, saving countless lives around the world."
A paper on the study – which also involved scientists from the University of São Paulo in Brazil and the University of York in the UK – was recently published in the journal Optica.
Source: Optica