The device draws on the human body’s natural defence mechanism against metal intoxication: an organic substance in the bloodstream called a chelating agent, which can detect and bind to heavy metal ions.
After binding, it prevents the heavy metal ions from interacting with other molecules and enzymes in the body, and marks it for excretion from the body.
By combining a chelating agent with an optical measurement system, the Singapore group developed a compact and highly sensitive device that can be used to rapidly test water samples in the field. The team claims that the technology could also be integrated into appliances for domestic use, such as water filtration systems.
The new device comprises an optical fibre sensor modified with a chelating agent, and a laser that shines through it. This sensor is connected to a processing unit that displays the results of the water quality test.
In a water sample contaminated by heavy metals, the metal ions will bind to the chelating agent on the optical fibre sensor. This induces a shift in the output light spectrum, from which the device’s processing unit then calculates the concentration of heavy metals in the sample. The process takes about five minutes.
The method is claimed to offer considerable advantages over other approaches including laboratory tests, which typically take at least a day to complete, and a host of existing mobile alternatives. According to NTU associate Professor Yong Ken-Tye it is able to detect up to 24 types of metal contaminants, which is double the capacity of other commercially available water sensors.
The invention, which is described in the scientific journal ACS Sensors is incredibly sensitive: requiring just a few drops of a water sample into a disposable sensor cartridge to detect heavy metals at parts-per-billion precision.
Commenting on applications of the technology NTU’s Professor Tjin Swee Chua said: “The device can easily be integrated into any existing in-line water treatment plant. While our product is competitive enough to penetrate the market, we are still working to enhance and expand our water sensor product line. For instance, we are exploring ways to translate this technology for domestic use, such as in domestic water filtration systems and electric water kettles.”
The team is now working to further develop the technology through a spin-out firm Waterply. The company is working with local companies to collect more data to improve the accuracy of the device and is also collaborating with a state-owned company in China to develop next-generation water sensors that can tackle water pollution.
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