Rapid, Low-Cost Sensor Identifies Tiny Amounts of PFAS

A cutting-edge technology may present an affordable and rapid method for testing perfluoroalky and polyfluoroalkyl substances (PFAS), compounds associated with cancer and various health issues.

A sensor developed by MIT chemists can identify minuscule levels of PFAS, chemicals present in nonstick cookware, food packaging, and many other consumer products.

Due to their inability to decompose naturally, these substances are also called “forever chemicals.” They have been connected to numerous detrimental health outcomes, such as immune system and endocrine system disruption, cancer, and reproductive issues.

Using the new sensor technology, the researchers demonstrated that they could find PFAS levels in a water sample as low as 200 parts per trillion. In addition to providing a means for consumers to test their drinking water, their device may find application in sectors such as semiconductor and firefighting equipment manufacturing.

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.

Timothy Swager, John D. MacArthur Professor and Study Senior Author, Department of Chemistry, Massachusetts Institute of Technology

The research appears in the Proceedings of the National Academy of Sciences.

Sohyun Park, a Former Postdoc at MIT and the paper’s lead author, and Collette Gordon, a Graduate Student at MIT, are additional authors.

Detecting PFAS

Numerous consumer goods have coatings made with PFAS chemicals. Nonstick coatings are frequently used in water-repellent apparel, stain-resistant materials, grease-resistant pizza boxes, cosmetics, firefighting foams, and cookware.

These widely used fluorinated chemicals date back to the 1950s and can come from factories, sewage treatment facilities, and landfills and end up in the water, air, or soil. In all 50 states, they have been discovered in sources of drinking water.

Perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonate (PFOS), two of the most dangerous PFAS compounds, have an “advisory health limit” set by the Environmental Protection Agency as of 2023. According to these advisories, the maximum amounts of PFOA and PFOS in drinking water should be limited to 0.004 and 0.02 parts per trillion, respectively.

Currently, sending a water sample to a lab that uses mass spectrometry testing is the only way for consumers to determine if PFAS is present in their drinking water. However, this costs hundreds of dollars and takes weeks to complete.

The MIT team developed a sensor based on lateral flow technology, the same method used for quick COVID-19 and pregnancy tests, to provide a quicker and less expensive testing method for PFAS. The new sensor is embedded with a unique polymer called polyaniline, which can transition between semiconducting and conducting states when protons are added to the material in place of a test strip coated with antibodies.

The researchers placed these polymers onto a strip of nitrocellulose paper and then covered them with a surfactant that can extract fluorocarbons, like PFAS, from a droplet of water placed on the strip. This lowers the material’s electrical resistance because protons from the PFAS are pulled into the polyaniline and transformed into a conductor. The amount of PFAS present can be quantitatively measured using this change in resistance, which can be precisely measured using electrodes and sent to an external device like a smartphone.

This method only functions with acidic PFAS, which includes perfluorobutanoic acid (PFBA) and PFOA, two of the most dangerous PFAS.

A User-Friendly System

The current version of the sensor can detect concentrations down to 200 parts per trillion for PFBA and 400 parts per trillion for PFOA. This is not low enough to adhere to current EPA guidelines; however, the sensor only uses a small fraction of a milliliter of water. To meet the extremely low EPA advisory levels, the researchers are developing a larger-scale device that can filter approximately one liter of water through a polyaniline membrane. They believe this approach should increase the sensitivity by more than a hundredfold.

We do envision a user-friendly, household system. 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.

Timothy Swager, John D. MacArthur Professor and Study Senior Author, Department of Chemistry, Massachusetts Institute of Technology

A device like this might provide a quick and less costly substitute for the existing PFAS detection techniques. Commercially available filters can be used to reduce the levels of PFAS in household drinking water if they are found. Manufacturers of products containing PFAS may find the new testing method helpful in determining the safety of releasing the water used in their manufacturing process into the environment.

The study was supported by an MIT School of Science Fellowship to Gordon, a Bose Research Grant, and a Fulbright Fellowship to Park.

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