New sensor detects PFAS in water at extremely low levels and tells apart similar compounds, providing a practical tool for protecting water supplies and supporting environmental monitoring efforts.
(Nanowerk Spotlight) Across rivers, groundwater reserves, and even treated municipal supplies, ultra-trace amounts of synthetic “forever chemicals” have been detected in drinking water. These compounds, known as per- and polyfluoroalkyl substances (PFAS), are used in products as varied as stain-resistant fabrics, food packaging, and firefighting foams. Their carbon–fluorine bonds are among the strongest in organic chemistry, making PFAS highly resistant to breakdown. Once released, they persist for decades, moving through soil and waterways and accumulating in living organisms.
The health implications are serious. Some PFAS, including perfluorooctanoic acid (PFOA) and perfluorooctyl sulfonate (PFOS), have been linked to cancers, immune disruption, and developmental effects. Regulators in Europe and the United States now set allowable limits in drinking water at concentrations as low as parts per trillion, and in some cases far below that. Detecting chemicals at such low levels is technically demanding, especially outside a laboratory.
Current gold-standard methods, such as liquid chromatography coupled with tandem mass spectrometry, can reach the required sensitivity but depend on expensive instruments, trained operators, and lengthy sample preparation. They are not designed for routine or on-site monitoring, leaving communities without a practical way to track contamination in real time.
A team of researchers in Italy has developed a sensor that addresses these constraints. Their design uses an electrolyte-gated organic transistor (EGOT) with a gate surface engineered to selectively interact with PFAS. The approach takes advantage of the “fluorophobic” effect, in which fluorinated molecules prefer to associate with other fluorinated surfaces, turning a subtle chemical tendency into a precise electrical signal.
The sensor’s gate electrode is coated with a self-assembled monolayer (SAM) made from two types of molecules. Most of the surface is covered by oligoethylene glycol (OEG), which prevents unwanted binding by other substances in water and improves compatibility with the aqueous environment. Embedded within this layer are domains of perfluorodecanethiol (PFDT), whose fluorinated chains attract PFAS molecules through multiple fluorine–fluorine interactions. The arrangement allows PFAS molecules in water to move across the OEG and bind to PFDT sites, while excluding many non-fluorinated compounds.
How the PFAS sensor works. The device is an organic transistor whose gate electrode is coated with a special molecular layer containing both fluorinated and non-fluorinated regions. PFAS molecules in water are drawn to the fluorinated areas, where their chemical chains line up with the surface. This interaction changes the electrical signal in the transistor, allowing the sensor to detect even tiny amounts of PFAS and tell apart similar compounds. (Image: Reprinted from DOI:10.1002/adfm.202508425, CC BY) (click on image to enlarge)
The researchers tested three PFAS with different chain lengths: perfluorobutanoic acid (PFBA) with four carbon atoms, perfluorohexanoic acid (PFHxA) with six, and PFOA with eight. When these molecules bind to the PFDT regions, their fluorinated tails interlock with the SAM’s fluorinated chains, producing a change in the electrical potential at the gate–water interface. This change shifts the transistor’s switch-on voltage and alters the current flowing through the device.
The number of fluorine–fluorine contacts increases with PFAS chain length, and the sensor could resolve differences in binding energy as small as 4 ± 1 kilojoules per mole, the contribution of a single –CF₂– group. This means the device can distinguish between PFAS molecules that differ by just one or two carbon atoms.
In performance tests, the EGOT achieved detection limits of 0.04 parts per trillion for PFOA, 1.2 parts per trillion for PFHxA, and 2.5 parts per trillion for PFBA. These values meet or exceed current European and US regulatory requirements. The response is obtained in less than ten minutes, without the need for labels or secondary reagents.
Control experiments confirmed the selectivity of the approach. Non-fluorinated surfactants such as sodium dodecyl sulfate, and acids such as hexanoic acid, produced negligible responses, showing that the PFAS signal depends on fluorine–fluorine interactions rather than general chemical binding.
To interpret the data, the team applied both standard transistor models and a framework tailored to organic transistors. This analysis showed that the main driver of the sensor signal is the change in switch-on voltage caused by PFAS binding, with minimal influence from changes in capacitance. The relationship between PFAS chain length and binding free energy was linear, with each additional –CF₂– group increasing the binding strength by about 4 kilojoules per mole.
The device was also tested with bottled water spiked with PFHxA to assess performance in a real sample. The results matched those in distilled water, though dissolved minerals caused slight variations at higher concentrations. Such effects could be addressed with calibration, allowing the device to be used with different water sources.
Because the EGOT platform is small, portable, and inexpensive to fabricate, it could be deployed directly in the field for environmental monitoring. The researchers suggest that by altering the design of the fluorinated SAM, the device could be adapted to detect other PFAS types, including branched or more complex structures. Arrays of such sensors could provide detailed chemical profiles of PFAS contamination, enabling more targeted remediation efforts.
This work demonstrates that molecular-level surface design can give portable sensors both the sensitivity and selectivity required for modern PFAS regulation. By translating subtle chemical interactions into clear electrical signals, the EGOT sensor offers a practical route to rapid, ultra-low-level detection in real-world water samples.
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ORCID information
Fabio Biscarini (University of Modena and Reggio Emilia)
, 0000-0001-6648-5803 corresponding author
Marcello Berto (University of Modena and Reggio Emilia)
, 0000-0002-3356-8829 corresponding author
Rian Zanotti (University of Modena and Reggio Emilia)
, 0009-0002-6396-4256 first author
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