Plasmon-enhanced fluorescence in nanomolar dye solution using combination of core-shell nanostructures of various shell thicknesses

Enhancement in fluorescence of samples in solution phase is very crucial for many practical applications. Herein, we report the fluorescence enhancement of a nanomolar solution using Ag core-silica shell nanostructures synthesized independently. Coumarin 6H dye solution has been taken as a case study. Three different Ag core – silica shell nanostructure solutions were prepared by varying the amount of reagent in Stöber method. The core-shell nanostructures were characterized by atomic force microscopy, dynamic light scattering, and UV–Visible spectrophotometry. The maximum values of fluorescence enhancement (η_max) were found to be 2.5, 4.3, and 1.5 when respective solutions with average nanoshell thicknesses of 2.4, 16.7 and 28.3 nm were used individually. However, the value of η_max increased by an order (η_max ~13) when the mixture of the nanoshell solutions was used. The reason behind the improvement in η was ascribed to the optimization in the values of the distance (r) between nanoshell and dye molecules as well as the separation (d) between the nanoshells. This report, as we believe, will enable the scientific community in obtaining better enhancement in the fluorescence signal of labeled proteins and fluorescent molecules in aqueous media with ease.