Low-cost and highly sensitive conductive polymer-based lateral flow assay for per- and polyfluoroalkyl substances detection

The performance of F-PANI-based e-LFA was optimized to achieve high sensitivity, selectivity, and reproducibility. Optimization focused on fine-tuning the F-PANI dispersion and refining the deposition of test lines on the nitrocellulose membrane. Test lines with a width of 0.7 cm consistently delivered reliable results across varying PFOA concentrations, whereas wider lines exhibited non-uniform protonic doping, leading to higher resistance values and increased variability. Additionally, maintaining proper hydration during the testing process was critical for ensuring consistent conductivity readings, as dehydration could result in signal degradation. Conductivity measurements were most accurate when conducted within five minutes of exposure to an aqueous PFAS solution, minimizing dehydration effects. The F-PANI-based e-LFA demonstrated remarkable sensitivity, with a detection limit of 400 ppt for PFOA and 200 ppt for PFBA. Although it has not yet achieved the 1 ng L⁻1 sensitivity levels of LC-MS, the accumulative nature of this method indicates promising potential for further optimization as a field-based, portable, and cost-effective approach capable of meeting the required ng L detection thresholds. The sensor also demonstrated high selectivity for PFAS, evidenced by its strong response to fluorous compounds while effectively excluding non-fluorous analogs such as butyric acid, which showed a 10,000-fold lower conductivity. Furthermore, the sensor consistently performed well in both deionized and real tap water, confirming its practicality for real-world applications. However, since key parameters of the water samples, such as pH, ionic strength and free chlorine level, were not specified, further testing is necessary to assess potential interferences in diverse water samples.