UV poop test: Samples water

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  • Published: Jun 1, 2014
  • Channels: UV/Vis Spectroscopy
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Water waste

Technology capable of sampling water systems to find indicators of fecal matter contamination that are thousandths and even millionths of times smaller than those found by conventional methods is being developed by US researchers (Credit: Texas A&M University)

Contamination of water with fecal matter is a serious risk, especially in the developing world, for several diseases that are often lethal. Now, UV technology capable of sampling water systems to find indicators of fecal matter at levels thousandths or even millionths of times lower than those detected by conventional methods has been developed by a team of researchers at Texas A&M University.

Vladislav Yakovlev, Marlan Scully, Joel Bixler, Michael Cone, Brett Hokr, John Mason and Ellie Figueroa of TAMU in College Station have developed an ultrasensitive technology for detecting the molecules that are ubiquitous in water contaminated with human or animal fecal matter. Conventional techniques capable of detecting such low concentrations are cumbersome, expensive or inadequate despite the importance of revealing contamination to avoid risk of serious and even fatal disease associated with feces.

In research funded by the US National Science Foundation, the team has developed an affordable, highly sensitive, easy to implement system capable of analyzing water samples in real time rather than the samples having to be sent back to a laboratory. That combination of benefits, says Yakovlev, makes it ideal for widespread use across the globe where putative water-quality problems are an issue.

Mellow yellow

Animal and human waste can contaminate both recreational and source waters, carrying the pathogens for various diseases such as polio, typhoid and cholera. Fecal contamination is also of environmental concern, damaging aquatic ecosystems and triggering so-called red-tide algal blooms. Contamination can be mitigated if samples from water systems are thoroughly analysed so that appropriate clean-up actions can be undertaken or a source of serious contaminations spotted before serious contamination takes place. Yakovlev explains that high cost, sample-size limitations and lengthy analysis times have previously limited the work of environmental researchers.

The team's new approach turns to a compound known as urobilin. Urobilin is a byproduct excreted in the urine and feces of many mammals, including humans and livestock such as cows, horses and pigs. Also known as urochrome it is a yellow linear tetrapyrrole compound; a breakdown product of the heme unit present in hemoglobin and some enzymes. Urobilin is formed via a rather circuitous pathway. Waste heme is converted to biliverdin and then to bilirubin, bilirubin is excreted in bile, degraded by microbial activity in the large intestine to urobilinogen and then reabsorbed into the bloodstream to be oxidized to urobilin for renal excretion. Urobilin is a relatively small molecule that can diffuse rapidly in water to occupy large volumes, such as lakes and reservoirs.

Fortunately, urobilin is phosphorescent when associated with zinc ions. Thus, if the chemical is present in water, adding zinc ions, can be used to make it glow green under ultraviolet light. The phosphorescence is weak when urobilin is present at low concentrations. Now, Yakovlev and his team have developed an approach that allows them to excite even tiny quantities of urobilin in large samples of water and detect any emission using an "integrated cavity".

The integrated cavity is essentially a hollow, cylindrical container. The sample is placed in the cylinder with a zinc solution. Ultraviolet laser light shone into the cylinder through a small opening excites any urobilin present. Any light emitted can only escape through the same hole through which the laser light enters so it can be collected efficiently and measured spectroscopically or by photo detector. Employing the integrated cavity in their detection efforts, Yakovlev's team has quantitatively detected the presence of urobilin down to femtomolar concentrations.

Supersize sample

"We can demonstrate detection of ultralow concentrations of urobilin in solution," Yakovlev explains. "This is a huge improvement in terms of sensitivity, and our technique has tremendous potential for analysis of global drinking water supplies, particularly in developing nations and following natural disasters, where sophisticated laboratory equipment may not be available."

Yakovlev explains that the technology can be produced for a few hundred dollars and can handle large samples, which is important as it is difficult if not impossible to get an accurate analysis of an overall water system based on conventional small samples. A larger sample gives researchers a better predictive power about the water that the system contains, says Yakovlev.

"The bigger the sample, the better," Yakovlev says. "And with our technology the sensitivity scales with the amount of water in our sample." Using one litre will increase sensitivity by a factor of 20. A 10-litre sample will give sensitivity an order of magnitude greater still. Yakovlev and colleagues are hoping to commercialize the technology. Its instantaneous results are a big advantage for domestic water supply testing. Think smoke detector for drinking water, Yakovlev suggests. He adds that the same technology could be used to detect other types of toxic compounds in liquids and gases for anti-terrorism applications, among other uses, for instance.

Related Links

Proc Natl Acad Sci, 2014, 111, 7208-7211: "Ultrasensitive detection of waste products in water using fluorescence emission cavity-enhanced spectroscopy"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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