MIT chemists have developed a sensor that detects tiny amounts of perfluoroalkyl and polyfluoroalkyl substances (PFAS). These chemicals are found in food packaging, nonstick cookware, and many other consumer products.
These compounds have been linked to a variety of adverse health effects, including cancer, reproductive problems, and disruption of the immune and endocrine systems.
Detect PFAS Levels as Low as 200 parts per Trillion
Using the new sensor technology, the researchers showed that they could detect PFAS levels as low as 200 parts per trillion in a water sample.
The device they developed could provide a way for consumers to test their drinking water. It could also be useful in industries that rely heavily on PFAS chemicals, including semiconductor manufacturing and firefighting equipment.
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There's a real need for these sensor 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 and senior author of the study, which appears this week in the Proceedings of the National Academy of Sciences.
Coatings containing PFAS chemicals are used in thousands of consumer products. In addition to nonstick coatings for cookware, they are commonly used in water-repellent clothing, stain-resistant fabrics, grease-resistant pizza boxes, cosmetics, and firefighting foams. Widespread since the 1950s, these fluorinated chemicals can be released into water, air, and soil from factories, wastewater treatment plants, and landfills. They have been found in drinking water sources in all 50 states.
Curious about PFAS? Dive into this article for more information!
Designed a Sensor Based on Lateral Flow Technology
In 2023, the Environmental Protection Agency established an "advisory health limit" for two of the most dangerous PFAS chemicals, known as perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonate (PFOS). These advisories call for a limit of 0.004 parts per trillion for PFOA and 0.02 parts per trillion for PFOS in drinking water.
Currently, the only way for a consumer to determine if their drinking water contains PFAS is to send a water sample to a laboratory for mass spectrometry testing. However, this process takes several weeks and costs hundreds of dollars.
To create a cheaper and faster way to test for PFAS, the MIT team developed a sensor based on lateral flow technology - the same approach used in Covid-19 rapid tests and pregnancy tests. Instead of a test strip coated with antibodies, 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 this polymer onto a strip of nitrocellulose paper and coated it 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 pulled into the polyaniline, turning it into a conductor and reducing the material's electrical resistance. This change in resistance, which can be precisely measured with electrodes and transmitted to an external device such as a smartphone, provides a quantitative measure of how much PFAS is present.
This approach only works with PFAS that are acidic, which includes two of the most harmful PFAS - PFOA and perfluorobutanoic acid (PFBA).
Offering Inexpensive Alternative to Current Detection Methods
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 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 polyaniline membrane, and they believe this approach should increase sensitivity more than 100-fold, with the goal of meeting the very low EPA advisory levels.
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We envision an easy-to-use, household system," says Swager.
"You can imagine putting in a liter of water, running it through the membrane, and having a device that measures the change in resistance of the membrane.”
Such a device could provide a cheaper, faster alternative to current PFAS detection methods. If PFAS are detected in drinking water, there are commercially available filters that can be used on household drinking water to reduce those levels. The new testing approach could also be useful for factories that manufacture products with PFAS chemicals, so they can test whether the water used in their manufacturing process is safe to release into the environment.
Source: Massachusetts Institute of Technology