Large-area crack-free Au-SiO2 2D inverse opal composite films: Fabrication and SERS applications

Plasmonic-photonic metallo-dielectric structures have attracted recent research interests due to their novel optical properties. Au-SiO2 based photonic structures have been built and have shown promising applications for example, as SERS substrates. However, due to the lack of control over the constraints in the various stages of conventional colloidal crystal templating approach, monolayer metallo-dielectric inverse opal structures have not been widely reported. In this work, a 2D hexagonal inverse opal (IO photonic structure of Au nanoparticles (NP) embedded in a SiO2 matrix is constructed using a new strategy. Here in, a binary Au-SiO(s)ol was infiltrated into the accommodative interstices of 2D self-assembled polystyrene (PS) spheres in an air-water interface. Effective removal of the PS spheres by chemical method resulted in Au-SiO2 IO structures. Optical properties of these structures show interesting plasmonic-photonic coupling. When they are used as substrates for Raman signal enhancement of crystal violet, they show better enhancement than either Au nanoparticles aggregates or Au-SiO2 non-photonic structures. The Au-SiO2 IO structures were also used to perform Raman spectroscopy analysis of astaxanthin rich shrimp oil, a novel value-added product extracted from the water used in shrimp processing. The surface enhanced Raman spectra showed the presence of favourable esterified form of astaxanthin in shrimp oil.