MIT sensor can detect harmful ‘forever chemicals’ in drinking water

MIT chemists have created a sensor that can detect small amounts of perfluoroalkyl and polyfluoroalkyl substances (PFAS). These chemicals, often referred to as “forever chemicals,” are present in many consumer products, including food packaging and nonstick cookware.

Because they do not break down naturally, these compounds have been associated with various harmful health effects, such as cancer, reproductive issues, and disruption of the immune and endocrine systems.

Researchers are using new sensor technology to detect PFAS levels as low as 200 parts per trillion in water samples. This could be a game-changer, as it provides a way for consumers to test their drinking water and industries that use PFAS chemicals to monitor their usage. The device could prove particularly useful for industries like semiconductor manufacturing and firefighting equipment.

“There’s a real need for these sensing technologies. We’re stuck with these chemicals for a long time, so we need to be able to detect them and get rid of them,” says Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT.

Coatings containing PFAS chemicals are present in so many everyday products. Apart from nonstick cookware, they are also used in water-resistant clothing, stain-resistant fabrics, and even cosmetics. These chemicals have been used for so long and can be released into the environment from many sources, including factories and landfills. They have been found in drinking water sources in all 50 states.

Recently, in 2023, the Environmental Protection Agency issued an “advisory health limit” for two of the most dangerous PFAS chemicals: perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonate (PFOS). This advisory recommends a limit of 0.004 parts per trillion for PFOA and 0.02 parts per trillion for PFOS in drinking water.

It’s not easy for consumers to determine if their drinking water contains PFAS. The only way to do so is to send a water sample to a laboratory that performs mass spectrometry testing. Unfortunately, this process takes several weeks and can be quite costly, amounting to hundreds of dollars.

Now, a team from MIT has devised a solution to create a cheaper and faster way to test for PFAS. They designed a sensor using lateral flow technology, the same approach used for rapid Covid-19 tests and pregnancy tests. The new sensor is embedded with a special polymer called polyaniline, which can switch between semiconducting and conducting states when protons are added to the material.

The researchers deposited these polymers onto a nitrocellulose paper strip, which was then coated with a surfactant capable of drawing out fluorocarbons like PFAS from a water droplet placed on the strip. As a result, protons from the PFAS were absorbed into the polyaniline, causing it to become a conductor and reduce the material’s electrical resistance. The decrease in resistance, which could be accurately measured through electrodes and communicated to an external device such as a smartphone, provided a quantitative estimate of the amount of PFAS present.

This technique works only with acidic PFAS, which include two of the most hazardous PFAS: PFOA and perfluorobutanoic acid (PFBA).

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 currently developing a larger-scale device that can filter about a liter of water through a polyaniline membrane. They believe this approach should increase the sensitivity by more than a hundredfold, with the ultimate goal of meeting the very low EPA advisory levels.

“We do envision a user-friendly, household system,” Swager says. “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.”

This device could offer a less expensive, rapid alternative to current PFAS detection methods if successful. In the event that PFAS are detected in drinking water, commercially available filters can be used to reduce those levels in household drinking water.

Additionally, this new testing approach could prove to be useful for factories that manufacture products with PFAS chemicals. They can use the device to test whether the water used in their manufacturing process is safe to release into the environment.

Journal reference:

Park, Sohyun; Gordon, Collette T.; Swager, Timothy M. Resistivity Detection of Perfluoroalkyl Substances (PFAS) with 6 Fluorous-Polyaniline in an Electrical Lateral Flow Sensor. PNAS, 2024.

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