A gold nanoparticle-enhanced methylene blue electrochemical sensor for detecting waterborne anionic surfactants and PFAS

Anionic surfactants (ASs) represent a class of contaminants persistently released into aquatic environments, with anionic fluorinated surfactants emerging as a significant concern due to their potential to infiltrate potable water and pose a threat to human health. Therefore, the development of novel tools for their early detection is crucial. In this study, the methylene blue (MB) redox probe, previously known for its selectivity towards ASs, was electropolymerized onto the surface of carbon nanotube-modified graphite screen-printed electrodes. The electroanalytical ability of the platform was tested by cyclic (CV) and square-wave (SWV) voltammetries upon the addition of sodium dodecyl sulfate as model analyte, due to its ubiquitous presence in the environment. A comprehensive exploration of key factors, such as scan cycles, optimal instrumental parameters, and pH effect was undertaken, revealing a stable and controlled redox response. To further enhance the sensitivity and detection capabilities of the MB-based sensor, gold nanoparticles (AuNPs) were incorporated, forming MB@AuNPs-modified electrodes. This enhanced system demonstrated excellent linearity (0.05–1 ng/mL and 5–50 ng/mL), high reproducibility, and improved detection limits (8.5 pg/mL and 0.23 ng/mL), attributed to the synergistic effect of MB and AuNPs in boosting the reduction current. The sensor was successfully applied to wastewater samples, benchmarked against the MBAS reference method, and further validated for the detection of two long-chain PFAS in drinking water. Supported by quantum mechanical calculations and optical studies, this proof-of-concept platform represents a sustainable approach for efficient water quality monitoring and management.