Key Findings
The developed fiber-optic SPR sensor demonstrates a concentration-dependent optical response to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). The sensor exhibited higher sensitivity and a lower detection limit for PFOA, with a maximum sensitivity of 3.59 nanometers per micromolar and a detection limit of 1.40 micromolar. In comparison, PFOS showed a maximum sensitivity of 2.76 nanometers per micromolar and a detection limit of 4.73 micromolar.
Technical Details
The sensor utilizes copper oxide nanoparticles functionalized with trimesic acid to create a chemically tunable interface. Copper oxide was selected for its ability to enhance the refractive index sensitivity of fiber-optic SPR platforms and its capacity for ligand functionalization. The team verified the surface modification using several characterization methods:
- FTIR and thermogravimetric analysis
- TEM and SEM
- Dynamic light scattering (DLS) and zeta potential measurements
Cryogenic-TEM revealed primary particle diameters of approximately 6 nanometers. However, DLS measurements indicated that these nanoparticles form micron-scale hydrodynamic aggregates when in aqueous suspension.
Background and Context
X-ray photoelectron spectroscopy analysis suggests that the stronger response to PFOA is due to its greater retention at the functionalized sensing interface. Despite this, the researchers noted that the specific molecular interactions causing the differential response between the carboxylic acid-terminated surface and the sulfonate-headgroup of PFOS have not yet been fully elucidated.
Significance and Outlook
This research demonstrates that trimesic acid functionalization of copper oxide nanoparticles provides a simple, tunable interface for the optical sensing of PFAS. Because the results were obtained from a fabricated platform under controlled laboratory conditions—and given the observed aqueous aggregation and unresolved interaction mechanisms—the reported sensitivities describe a laboratory device rather than a validated method for field deployment.
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