In Situ Preparation of Plasmonic Gold Nanoparticle-Supramolecular Hydrogel Nanocomposites with Tunable Optical Properties: Correlating Theory and Experiments

Supramolecular plasmonic polymer nanocomposites are versatile soft materials that hold great promise for many bioapplications as they combine the functional properties of inorganic nanoparticles with the dynamic nature of the polymer matrix. Herein, we exploited the supramolecular chemistry and reducing properties of plant-derived gallic acid (GA) to drive the in situ formation of gold nanoparticles (Au NPs) into poly­(vinyl alcohol) (PVA)–GA hydrogels. The size and shape of Au NPs in the plasmonic nanocomposites were tuned from 25 to 221 nm and from anisotropic to spherical, respectively, varying the Au3+ concentration. From experimental and theoretical simulation of the extinction spectra, it was possible to assess the change of the average refractive index of the surrounding Au NPs in two Au3+ concentration regimes. The changes of the chemical environment were also tested by Raman and infrared spectroscopy characterization. Furthermore, the viscoelastic behavior of the supramolecular PVA–GA hydrogel was also investigated for the plasmonic nanocomposites. At the highest concentration investigated, the formation of Au NP aggregates (dimers and trimers) was observed and rationalized with electrodynamic simulations. Finally, the surface-enhanced Raman spectroscopy properties were also analyzed using Rhodamine 6G, revealing the extraordinary capacity of these materials for their application as sensing platforms.