An MIT sensor can detect “forever chemicals” known as PFAS in drinking water. PFAS are found in many consumer products and are linked to cancer and other health problems. Credit: MIT News; iStock
Key points:
- Researchers are working on a device that could eventually be installed in a home to test drinking water for PFAS.
- Currently, only laboratories can test for the forever chemical, using high-tech techniques like mass spectrometry.
- The new sensor is based on lateral flow technology—the same approach used for rapid COVID-19 and pregnancy tests.
One of the keys to PFAS research is the ability to detect the "forever chemicals" at increasingly lower and lower quantities. In their latest research, MIT researchers have taken a step toward that goal with the design of a new sensor that can detect PFAS levels as low as 200 parts per trillion in a water sample.
Last year, the EPA created an advisory health limit for two of the most hazardous PFAS chemicals—0.004 parts per trillion for perfluorooctanoic acid (PFOA) and 0.02 parts per trillion for perfluorooctyl sulfonate (PFOS).
While laboratories can test water samples for PFAS utilizing mass spectrometry, consumers at home do not have that ability. To try to put that power in the hands of people, the MIT team designed a new sensor based on lateral flow technology—the same approach used for rapid COVID-19 and pregnancy tests. But instead of a test strip coated with antibodies, the new sensor is embedded with a special polymer known as polyaniline, which can switch between semiconducting and conducting states when protons are added to the material.
The researchers deposited these polymers onto a strip of nitrocellulose paper and coated them with a surfactant that can pull fluorocarbons such as PFAS out of a drop of water placed on the strip. When this happens, protons from the PFAS are drawn into the polyaniline and turn it into a conductor, reducing the electrical resistance of the material. This change in resistance, which can be measured precisely using electrodes and sent to an external device such as a smartphone, gives a quantitative measurement of how much PFAS is present.
The current version of the sensor can detect concentrations as low as 200 parts per trillion for PFBA, and 400 parts per trillion for PFOA. This is not quite low enough to meet the current EPA guidelines, but the sensor uses only a fraction of a milliliter of water. The researchers are now working on a larger-scale device that would be able to filter about a liter of water through a membrane made of polyaniline, and they believe this approach should increase the sensitivity by more than a 100x, with the goal of meeting the very low EPA advisory levels.
“We do envision a user-friendly, household system,” said senior author Timothy Swager, professor of chemistry at MIT. “You can imagine putting in a liter of water, letting it go through the membrane, and you have a device that measures the change in resistance of the membrane.”