Glass of clean drinking water

Heavy-metal contaminants in drinking water detected in minutes by portable device

Image credit: Luchschen |

Scientists from Nanyang Technological University (NTU) in Singapore have invented a portable device that can detect trace levels of heavy metal contaminants in drinking water within five minutes.

Taking inspiration from the human body’s natural defence mechanism against metal intoxication, the device uses an organic substance found in the human bloodstream called a chelating agent, which detects and binds 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.

Associate professor Yong Ken-Tye, one of the scientists behind the device, said the use of a chelating agent ensures its detection is as sensitive as “the body’s natural defence mechanism against metal poisoning”.

Combining the chelating agent with an optical measurement system, the Singapore researchers developed a compact and hand-held sensitive device that can be used to rapidly test water samples in the field.

This combination only required a few drops of water sample in a disposable sensor cartridge to detect heavy metals at parts-per-billion precision, meaning the device can detect lead levels of five parts per billion – more precise than the 10 parts per billion limit specified by the Environmental Public Health Act in Singapore.

The device generates test results quickly without the need to bring samples back to laboratories, facilitating on-site water testing

The device generates test results quickly without the need to bring samples back to laboratories, facilitating on-site water testing

Image credit: NTU Singapore

The 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.

If a water sample is contaminated by heavy metals, the metal ions will bind to the chelating agent on the optical fibre sensor.

This binding process prompts a shift in the output light spectrum, from which the device’s processing unit than calculates the concentration of heavy metals in the sample – a process which takes about five minutes.

Typically, drinking water quality monitored using highly accurate laboratory tests can take at least a day to complete, according to the NTU scientists. These laboratory tests are necessary as heavy metals cannot be identified by colour, taste or odour unless they are present at high levels.

While there already are portable devices on the market that can quickly detect heavy-metal contaminants, NTU said they might require the additional step of mixing the water sample with a buffer solution before performing the test.

According to Professor Ken-Tye, the device they invented is able to detect up to 24 types of metal contaminants - double the capacity of other commercially available water sensors.

“The device can easily be integrated into any existing in-line water treatment plant,” Tjin Swee Chua, NTU professor, said when commenting on the applications of the technology.  

“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.”

Associate Professor Yong Ken-Tye (left) and PhD student Stephanie Yap are part of the team behind the device

Associate Professor Yong Ken-Tye and PhD student Stephanie Yap are part of the team behind the device

Image credit: NTU Singapore

The team is now working to further develop the technology and to use the device in parts of Asia such as China, Pakistan and India where there is serious water pollution, with the scientists aiming to make the device commercially available in about two years.

“In remote areas, villagers can use the device to monitor the quality of water collected from the wells,” Professor Ken-Tye added.

Furthermore, the scientists are developing an app to store data from lakes and rivers in parts of Asia so that countries can track the changes in water quality over time.

“For instance, officials in India can test the water quality of a pond during the monsoon season,” said Ken-Tye. “The data collected in the app will show a trend in the amount of heavy metals in the water body over the months. The trend will help them predict the water quality over the next few months and for the next monsoon season.”

In March 2019, researchers from the University of Edinburgh developed a biosensor that attaches to a smartphone and uses bacteria to detect unsafe arsenic levels – a device that could help millions of people avoid drinking contaminated water.

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