Theme: 07. Per- and Polyfluorinated Alkyl Substances (PFAS)

Topic Area: 7m. PFAS Site Characterization

Formatted Title:

Molecularly Imprinted Polymer (MIP)-Based Electrochemical Sensor for Rapid Detection of Poly- and Per-Fluorinated Alkyl Substances (PFAS) On Site

Background/Objectives:

Poly- and per-fluorinated alkyl substances (PFAS) are a human health concern that have been found in water supplies around the world. The current testing paradigm is to collect samples of water and send them to third-party laboratories for liquid chromatograph-tandem mass spectrometry (LC-MS/MS) analysis. This testing is costly, and the turnaround time for results can be weeks to months. Thus, there is great need for a low-cost, rapid, in-field screening sensor for PFAS. Such a sensor could enable targeted screening to reduce the number of samples sent for LC-MS/MS analysis, monitor progress of destructive remediation technologies on site, and alert water treatment plants when PFAS escapes their granular activated carbon (GAC) or ion-exchange resin (IX) systems.

Approach/Activities:

Molecularly imprinted polymers (MIPs) are polymers created in the presence of a specific analyte, known as a template. The template and polymer monomers establish attractive intermolecular forces that are maintained during the polymerization, creating sites with high specificity towards the template. The template is then removed through washing, resulting in a polymeric material with pores that have a lock-and-key binding mechanism for the chosen template. The polymers can be controllably generated on an electrode surface via electropolymerization. This templated MIP acts as an insulator, limiting current at the electrode surface. When the template is removed, the current increases because an electron mediator can access the electrode through the empty binding sites. When the MIP encounters the template molecule (e.g., PFOS), sites in the MIP become occupied, blocking access to the electrode surface and decreasing the current sigmoidally with concentration. Although these sensors have been demonstrated in the past, we found that they are prone to false positives and have developed several new manufacturing methods to improve sensor accuracy.

Results/Lessons Learned:

When testing the MIP manufacturing methods of prior research, we found that the background response (response in uncontaminated water samples) decayed over time resulting in false positives. We were able to stabilize the background response by electropolymerizing the MIP in an acidic solution, soaking in water or other sensing media overnight to “condition” the sensor, and separating the sample solution from the electron mediator measurement solution. These changes resulted in MIP sensors with a more stable signal over time in both uncontaminated and PFAS-spiked water samples. With a stable response to uncontaminated water samples, MIP electrochemical sensors will be more viable for reliably detecting PFAS contamination for near real-time, on-site testing.

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Casey Smith