PFAS have been widely used because of their chemical and thermal stability, but that same durability makes them persistent in the environment. With regulations increasingly strict on their use, there is a growing demand for faster, simpler ways to check water for PFA contamination on site.
Standard PFAS testing usually relies on chromatography and mass spectrometry. Those methods are sensitive but require complex sample preparation, costly equipment, and trained operators, limiting their use outside specialist laboratories.
The Benzoxadiazole Fluorophore Sensor
The sensing probe is built on a benzoxadiazole fluorophore linked to a guanidine group. Its recognition mechanism relies on protonation-mediated hydrogen bond-assisted ion pairing, making it responsive to strong rather than weak acids. In this assay, that property is used to detect PFAAs from water.
When a target analyte binds, the probe’s fluorescence increases in organic media, creating a direct optical readout. Under the study conditions, the system is selective for strong hydrophobic organic acids, including PFAAs.
Two Detection Formats
The first format uses biphasic liquid-liquid extraction inside a droplet-based microfluidic device. An aqueous sample is combined with an organic phase containing the probe, allowing rapid phase transfer and binding inside droplets.
This setup works with sample volumes below 100 μL and uses laser-diode excitation with photomultiplier-based fluorescence detection.
The second format embeds the probe in a polymer layer coated onto submicron silica particles. That creates a local organic environment around the sensing unit and allows direct detection in water without a solvent-extraction step. In this version, the system was shown to work in water samples at pH ≥ 4.
PFA Detection Results
The probe responded strongly to long-chain PFAAs, including PFOA and PFOS. PFOS showed the strongest apparent binding, while medium- to long-chain perfluorocarboxylic acids showed broadly similar binding constants in ethyl acetate.
In biphasic cuvette tests, the limit of detection for PFOA was about 17.3 μM. In the microfluidic format, the concentration improved to 1.4 μM for PFOA and 0.5 μM for PFOS.
Environmental water samples could also be analysed, but sample treatment mattered. Without sufficient acidification, phase transfer was strongly suppressed. After optimized acidification and buffering, the system performed comparably to tests in pure water.
The particle-based format provided direct aqueous detection without organic solvents, with a limit of detection around 1.5 μM for PFOA.
In that system, HCl alone remained largely silent up to 0.5 mM, suggesting that the polymer shell helps separate responses to strong organic acids from those to inorganic acids under the tested conditions.
Usefulness for On-Site PFAA Detection
The platform delivers results in about seven minutes, uses low sample volumes, and keeps sample preparation relatively limited. It is best viewed as a low-micromolar method for onsite screening, containment, and remediation support, rather than a standalone tool for ultra-trace environmental monitoring. For that, additional preconcentration would still be needed.
The design is also modular, which could help future efforts to extend the approach to other PFAS subclasses.
Journal Reference
Pérez-Padilla V., et al. (2026). Detection of Perfluoroalkylic Acids From Water Using a Guanidine-Based Fluorescent Probe and Microfluidic Droplet Extraction. Advanced Sensor Research, 5, e70145. DOI: 10.1002/adsr.70145