PFAS constitute a very large family of molecules, some of which are now recognized as “forever chemicals.” While current regulations require the measurement of concentrations of only certain PFAS, the number of these compounds to be analyzed is still quite limited and could be much broader, provided that existing measurement methods are improved and new ones are developed, particularly through the design of portable sensors.

Per- and polyfluoroalkyl substances, better known by the acronym PFAS (pronounced “pifasse”), constitute a family of more than 12,000 synthetic molecules. These compounds contain very strong chemical bonds between carbon and fluorine atoms, which give them remarkable properties.

In particular, PFAS can possess non-stick, anti-friction, and water-repellent properties, combined with exceptional chemical and thermal stability. For these reasons, PFAS have been used since the 1950s in a wide range of industrial products (plastics, resins, paints, firefighting foams, etc.) and consumer goods (cosmetics, textiles, food packaging, etc.).

Unfortunately, some PFAS are now recognized as toxic and harmful to human health and the environment. Their high chemical stability makes them difficult to (bio)degrade, and some of them are now referred to as “forever chemicals.”

It is therefore necessary to limit the use of PFAS and address the environmental and health issues they cause. As a result, efforts are currently underway worldwide to regulate the use of PFAS, understand their effects on health and the environment, find alternatives to them, effectively decontaminate polluted sites, and ensure their monitoring and oversight.

In this context, a key issue is the ability to effectively detect and quantify PFAS, whether in the environment, drinking water, and wastewater, or in biological systems (body fluids, organs, etc.).

Unfortunately, the vast number of per- and polyfluoroalkyl substances, the wide variety of their properties, and the low detection limits that must be achieved make monitoring and analyzing them extremely complicated!

How are PFAS analyzed?

There are currently several methods for analyzing PFAS, but the majority of measurements are performed using a technique known as “liquid chromatography coupled with tandem mass spectrometry” (LC-MS/MS). This technique makes it possible to distinguish, identify, and quantify the various PFAS present in the initial sample.

This analytical technique combines the separation capabilities of liquid chromatography with the analytical capabilities of mass spectrometry, which is highly sensitive and selective.

This technique, which is widely used particularly in the pharmaceutical industry and by analytical and research laboratories, is extremely sensitive and effective, as it allows for the simultaneous analysis of a large number of molecules contained in complex samples with very low detection limits.

However, it is costly and difficult to implement, as it requires state-of-the-art equipment and expert users.

With this technique, we can only detect what we're looking for

In addition, it is necessary to use a chromatographic column suitable for the molecules to be analyzed. The instrument must also be calibrated; that is, PFAS samples with known molecular compositions and concentrations must be used beforehand so that the molecules can be identified and quantified during the analysis.

Therefore, we can only detect what we are looking for: this is why we refer to it as “targeted analysis.” Only a limited range of PFAS is detected in this way (typically, a few dozen are tested for), which can result in an underestimation of the total amount of PFAS present in a sample.

Furthermore, in the specific case of PFAS, these compounds can be found in a wide variety of matrices, including water (drinking water, natural water, industrial water, and/or wastewater), soil, and sludge, as well as biological media such as blood or organs. It is therefore often necessary to pretreat the sample to make it suitable for analysis.

This additional step significantly increases the time required to obtain results and raises the cost of each analysis, which can amount to several hundred euros. It is therefore easy to understand just how complex this type of analysis is!

Finally, PFAS measurements using chromatography are performed exclusively in the laboratory. Samples must therefore be transported, which increases the time between collection and the availability of the analysis results.

Will we soon be able to detect PFAS quickly and on-site?

Given the current challenges related to PFAS, there is strong demand for on-site analysis—particularly of environmental media and drinking water—to quickly detect potential contamination and enable a rapid and effective response.

To date, there is no simple test that can quickly detect PFAS directly at the site being analyzed (river, wastewater, etc.). Nor is it possible to continuously measure and monitor PFAS concentrations over time.

To address this issue, research is underway worldwide to develop simple sensors that enable rapid, low-cost detection. The goal is, in particular, to quickly and easily obtain a signal—usually electrical or optical—indicating the presence of PFAS in a sample.

It is in this context that the EDYTEM laboratory at the University of Savoie Mont-Blanc andthe Grenoble-based company GRAPHEAL (a CNRS spin-off startup resulting from research conducted at the Néel Institute in Grenoble) are collaborating on the development of a graphene-based electronic sensor.

Graphene, whose discoverers were awarded the Nobel Prize in 2010, is a two-dimensional, crystalline molecular film of carbon just one atom thick. When stacked, it forms graphite, and it possesses exceptional electrical properties because the electrons—forced to move along the surface of the film due to its extremely thin thickness—interact strongly with the elements adsorbed onto the graphene.

The principle behind the device in question—a transistor-type device—is based on connecting a graphene sheet to two electrodes, with the graphene material coated with a molecular film capable of selectively interacting with one or more PFAS-type molecules present in the sample to be analyzed. This interaction at the molecular level causes a change in the voltage between the two electrodes. Since the magnitude of this change is related to the concentration of PFAS molecules in the sample, it is then possible to quantify them.

Developing such a technique poses a real scientific challenge, as it involves measuring the equivalent of a single drop of water in a volume equivalent to three Olympic-sized swimming pools! It is also necessary to explore a wide range of PFAS molecules and experimental conditions, since PFAS can be present in a wide variety of samples, ranging from drinking water to wastewater.

To date, these methods can detect various types of PFAS currently being monitored, including PFAS with both long (more than 5 carbon atoms) and short fluorinated chains. Our detection limit is currently 40 nanograms per liter for PFOA, which is one of the PFAS most commonly found in trace amounts in the environment.

Preparation techniques that concentrate PFAS in the sample could further lower this threshold.

If successful, these sensors will enable rapid, low-cost testing that can be performed directly on-site. Much like COVID self-tests, which complement PCR tests, these graphene-based electronic sensors—just like other rapid testing devices, such as sensors based on a change in color — will complement chromatographic methods. They will yield more preliminary results, thereby facilitating enhanced monitoring that is better tailored to current PFAS-related challenges.