Simultaneous surface enhanced infrared absorption (SEIRA) with Fano resonance and refractive index (RI) sensing are proposed via a split-ring-resonator-based metamaterial perfect absorber (MPA) to detect polyvinyl chloride (PVC), a commonly used polymer but one that was recently prohibited in many areas such as Europe. This bifunctional sensor could provide a label-free and qualitative PVC detection through SEIRA coupled to the vibration mode and a quantitative measurement through RI sensing. To design the MPA, the main operating frequency is targeted at 615 cm−1 for C-Cl bond of PVC. Transition from a reflectance dip to a peak, i.e., Fano resonance was observed at y polarization in both simulation and experiments, evidencing the existence of PVC. On the other hand, to test the RI sensing ability of the MPA, different RI (from 1 to 1.5) of analytes and different thicknesses (from 109 to 1050 nm) of polymethyl methacrylate (PMMA) were applied to the MPA in simulation and experiments, respectively. The simulated sensitivities are 4045 and 2361 nm/RIU for the first and third modes of the MPA, respectively, while the measured sensitivities based on PMMA are 3713 and 1694 nm/RIU. Overall, the detection limit of PVC could be down to 0.5% in experiments, which outweighs the current measurement limit of 10% through infrared absorption measurement.
Improved Refractive Index-Sensing Performance of Multimode Fano-Resonance-Based Metal-Insulator-Metal Nanostructures
