Session: 14-04-01: Micro/Nano Devices and Medical Systems

Paper Number: 164979

Molecularly Imprinted Laser-Induced Graphene Sensor for Sensitive Perfluorooctanoic Acid (PFOA) Detection 

Per- and polyfluoroalkyl substances (PFAS) are persistent pollutants associated with serious health risks, including carcinogenicity and endocrine disruption. Among them, perfluorooctanoic acid (PFOA) is particularly concerning due to its prevalence in water sources. Detecting PFOA at ultra-low concentration is essential for effective environmental monitoring and regulatory compliance. Traditional methods like liquid chromatography-tandem mass spectrometry (LC-MS/MS) provide high sensitivity but are expensive, time-consuming, and require specialized facilities. Optical and plasmonic sensors, though capable of sub-ppt detection, often suffer from matrix interference and complex instrumentation, limiting their field applicability. This study introduces an electrochemical sensor that integrates a laser-induced graphene (LIG) electrode with a molecularly imprinted polymer (MIP) to offer a cost-effective, selective, and sensitive solution for rapid on-site PFOA detection.

This research presents an innovative approach to overcoming current analytical challenges in PFAS detection. The sensor employs a LIG electrode, produced via CO₂ laser ablation of a polyimide substrate, to generate a high-surface-area, conductive network. This is combined with a molecularly imprinted polymer layer—formed by electropolymerizing o-phenylenediamine in the presence of PFOA as a template—that creates binding sites specific to PFOA. This dual strategy not only enables the sensor to differentiate PFOA from similar compounds like perfluorooctanesulfonic acid (PFOS) and perfluorononanoic acid (PFNA) but also achieves a remarkable limit of quantitation (LOQ) of 0.025 ppt. The sensor’s rapid response and low fabrication cost make it a practical alternative for real-time, on-site environmental monitoring.

The sensor is fabricated by converting a polyimide substrate into a porous graphene electrode using CO₂ laser ablation, which rearranges the substrate’s carbon atoms to form a conductive network with high electrochemically active surface area. Next, the MIP layer is deposited by electropolymerizing o-phenylenediamine in the presence of PFOA, which serves as a template. After polymerization, the template is removed via solvent treatment, leaving behind selective binding sites for PFOA. Detection is performed using differential pulse voltammetry. When PFOA binds to the imprinted sites, it hinders the redox activity of a potassium ferrocyanide/ferricyanide probe at the electrode surface, leading to a decrease in peak current proportional to the PFOA concentration.

Scanning electron microscopy confirmed that the LIG electrode exhibits a porous, three-dimensional graphene structure that enhances electrochemical performance by increasing surface area. Raman spectroscopy showed distinct D, G, and 2D peaks, confirming the formation of high-quality graphene. Monitoring the electropolymerization process via cyclic voltammetry revealed that repeated scans result in a decreasing polymerization current due to the thickening of the MIP layer. Redox peaks diminished after polymerization and reappeared after template removal, indicating successful formation and extraction of the MIP template. Optimization experiments indicated that three laser ablation cycles yielded the best results, with the highest 2D/G ratio (indicative of thin graphene flakes) and the lowest D/G ratio (indicating minimal defects). Electrochemical tests showed that these conditions produced the highest redox peak intensities. The sensor demonstrated a broad linear detection range from 0.025 ppt to 25 ppb, with a sensitivity of 0.79 μA/decade. A LOQ of 0.025 ppt was demonstrated. Selectivity tests revealed that even when exposed to 250 ppb of PFOS and PFNA, the sensor’s response varied by less than 2.1% compared to 25 ppb PFOA, showing its strong molecular selectivity. 

This study presents a novel electrochemical sensor for PFOA detection that combines laser-induced graphene with molecularly imprinted polymer to deliver high sensitivity, ultralow detection limit, and high selectivity. A sensitivity of 0.79 μA/decade and a limit of quantitation of 0.025 ppt were demonstrated. The low-cost, scalable fabrication process and rapid response make this sensor a promising tool for real-time, on-site environmental monitoring. Future work will focus on testing the sensor with real-world samples, expanding detection to additional PFAS compounds, and integrating the system into portable platforms. This sensor represents a significant advancement in PFAS detection technology, offering a practical solution for environmental monitoring and regulatory compliance.

Presenting Author: Yingming Xu University of Minnesota

Presenting Author Biography: Yingming Xu received his B.S. degree in Mechanical Engineering from the University of Minnesota, Minneapolis, MN, USA, in 2020. He is currently pursuing his Ph.D. in Mechanical Engineering at the University of Minnesota under the supervision of Professor Tianhong Cui. His research interests include graphene-based field-effect transistors and MEMS-based microsensors for environmental applications.

Authors:

Yingming Xu University of Minnesota
Peng Zhou University of Minnesota
Tianhong Cui University of Minnesota