In this study, we investigate the third-order nonlinear optical properties of phenol red (PR) solutions and their hybrid composites, analyzing a PR solution with a pH of 7.56, a zwitterionic PR solution (PRz) with a pH of 1.52, and a PR-doped PVA/silica (PR-PS) hybrid composite made using an acid-catalysed sol-gel method and drop-casting technique. The PR-PS thin film exhibits a smooth and homogeneous surface, with a root mean square roughness (RMS) of 0.816 nm and an average roughness, Ra of 0.648 nm. FESEM was employed to analyze the surface morphology and thickness of the thin film, which was found to be approximately 80 µm. UV-vis analysis demonstrates that PR in the matrix is in its zwitterionic form, with absorption peaks at 450 nm and 515 nm. The PVA/silica hybrid matrix exhibits an enhancement in third-order nonlinear susceptibility, χ(3) by 83.94%. Moreover, our finding also indicates that the PR-PS hybrid composite’s β being being 79.09% and 99.37% larger than that of the PR and PRz samples, respectively. These results suggest that the PR-PS thin film is a promising material for photonic applications, such as nonlinear optical switching devices and optical limiting applications, due to its enhanced nonlinear optical properties.

This review aims to investigate the potential of various plasmonic materials for Coronavirus Disease 2019 (Covid19) detection in terms of performance, limitations and future prospects. A few parameters have been reviewed, such as sensitivity, the Limit of Detection (LOD), time response, and thickness of materials. This review analyses plasmonic materials used to excite the Surface Plasmon Resonance (SPR) effect, such as gold-based, silver-based, copper-based, and metal nanoparticles. In addition, the additional or hybrid materials are reviewed as well. Gold-based SPR sensors perform excellently in detecting various viruses, including Covid-19. The implementation of gold-based materials includes gold nanomaterial, which has different shapes, for instance, nanospheres, nanorods, and nanoislands. Obviously, the deployment of gold nanomaterials resulted in the best sensitivity. According to the analysis, about 50% of recent research chose gold nanomaterials as plasmonic materials for sensing applications concerning their outstanding properties such as high stability, oxidation resistance and simple fabrication. Besides gold nanomaterials, hybrid-based gold material such as graphene-gold based sensor exhibits a good sensitivity of about 183.3◦/RIU, in which 25% of current studies utilized this plasmonic material for virus detection. In conclusion, gold nanomaterials-based plasmonic sensors have a bright potential to be implemented for Covid-19 detection, and adding another material like graphene can enhance the performance. We believe that the output of this study will contribute to developing biosensors for detecting Covid-19.