Symmetric Metal Organic Framework-Plasmonic Architectures for Reversible and High-Sensitivity Optical Sensing

Plasmonic nanostructures have attracted considerable interest for their ability to manipulate light at the nanoscale. The optical response of these metallic architectures is greatly sensitive to changes in their surrounding environment, which makes them particularly interesting for sensing applications. Here, we report a versatile and highly sensitive plasmonic sensing platform that combines the surface lattice resonances (SLRs), sustained by 2D gratings of metal nanoparticles, and the exceptional refractive index tunability offered by ZIF-8 metal-organic framework (MOF) films. The SLRs provide narrow resonances that strongly depend on the surrounding refractive index, which can be modulated via solvent exchange in the ZIF-8. The plasmonic 2D arrays were fabricated using templated-assisted assembly of metal colloids; a scalable and gentle process that enabled the study of different ZIF-8/grating configurations. First, we studied ZIF-8 films on top of the 2D arrays, where an optimized concentration of the colloidal dispersion allowed dynamic and reversible ON/OFF tuning of the SLR response. Second, we explored the role of the refractive index mismatch between substrate and ZIF-8 superstrate. Finally, we fabricated 2D plasmonic gratings completely embedded within ZIF-8 layers, achieving enhanced sensing performance with a refractive index sensitivity of 427 ± 19 nm·RIU^{- 1}. These results highlight the potential of MOF-plasmonic hybrids as responsive and tunable nanophotonic platforms for next-generation optical sensing applications.