NTU Singa­pore sci­ent­ists invent hand­held device for quick mon­it­or­ing of drink­ing water quality

The secret lies in an organ­ic sub­stance with­in the cir­cu­lat­ing human 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. Com­bin­ing a che­lat­ing agent with an optic­al meas­ure­ment sys­tem, Asso­ci­ate Pro­fess­or Yong Ken-Tye andPro­fess­or Tjin Swee Chuan from the School of Elec­tric­al and Elec­tron­ic Engin­eer­ing developed a device that gen­er­ates test res­ults quickly without need­ing to bring samples back, mak­ing the device con­veni­ent for on-site water test­ing. It could also be integ­rated into appli­ances for domest­ic use, such as water fil­tra­tion sys­tems. Drink­ing water qual­ity is typ­ic­ally mon­itored via labor­at­ory tests as heavy metals can­not be iden­ti­fied by col­our, taste, or odour, unless present at high levels. Lab tests, while highly accur­ate, take at least a day to com­plete. There are some port­able devices on the mar­ket that can detect heavy met­al con­tam­in­ants quickly, but may require the addi­tion­al step of mix­ing the water sample with a buf­fer solu­tion before the test can be per­formed. The sensor for such kits also has to be used with­in 30 minutes after it is exposed to air, as the effect­ive­ness of the sensor can be affected by air, heat, or humid­ity. Oth­er mobile altern­at­ives include those that use met­al elec­trodes such as mer­cury as a sens­ing probe, which could intro­duce heavy met­al con­tam­in­ants back into the envir­on­ment, and test strips that change in col­our when they come into con­tact with heavy metals but leads to res­ults that rely on sub­ject­ive read­ings of the strip. The NTU inven­tion repor­ted in a paper pub­lished in the sci­entif­ic journ­al ACS Sensors works in the field and requires just a few drops of a water sample into a dis­pos­able sensor cart­ridge to detect heavy metals at parts-per-bil­lion pre­ci­sion. This level of sens­it­iv­ity is in line with the safety lim­it require­ments in Singa­pore that falls with­in the World Health Organisation’s stand­ards. For instance, the device can detect lead levels of 5 parts per bil­lion, which is lower than the 10 parts per bil­lion lim­it stip­u­lated by the Envir­on­ment­al Pub­lic Health Act in Singa­pore. The sens­it­iv­ity of the sensor in the NTU hand­held device is also not lim­ited by expos­ure to air, and remains effect­ive up to a tem­per­at­ure of 40°C. Assoc Prof Yong Ken-Tye, hold­er of the NTU Provost’s Chair in Elec­tric­al and Elec­tron­ic Engin­eer­ing, said, ​“Our device is cap­able of con­duct­ing on-site water qual­ity tests quickly and can detect up to 24 types of met­al con­tam­in­ants, which is double the capa­city of oth­er com­mer­cially avail­able water sensors. ​“Using a che­lat­ing agent in the device ensures that its sensor is as sens­it­ive in detect­ing heavy metals as the body’s nat­ur­al defence mech­an­ism against met­al intox­ic­a­tion.” Inspired by body’s met­al sens­ing mech­an­ism 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 (See image below). 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. Pro­fess­or Tjin Swee Chuan, who is also NTU’s Asso­ci­ate Prov­ost (Gradu­ate Edu­ca­tion & Lifelong Learn­ing), 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.” After fil­ing two pat­ents, the NTU team has now suc­cess­fully incor­por­ated a spin-off, Water­ply. It is now work­ing with oth­er loc­al com­pan­ies to col­lect more data through their inven­tion to improve the accur­acy of the device. Water­ply is also col­lab­or­at­ing with a state-owned com­pany in China to devel­op next-gen­er­a­tion water sensors that can tackle water pol­lu­tion. The research pro­ject was sup­por­ted by NTU’s Nan­yang Envir­on­ment and Water Research Insti­tute (NEWRI), and NTU­it­ive, NTU’s innov­a­tion and enter­prise com­pany. Source: Nan­yang Tech­no­lo­gic­al Uni­ver­sity, Media release, 15.04.2019