Preparation of optical functional composite films and their application in protein detection

In this work, an optical functional composite film was prepared through self-assembly technique for specific protein detection. The Au nanostructures with metal enhanced fluorescence (MEF) effect were prepared via the in situ reduction of Au ions in a filter paper. Then, a multilayer film was prepared on the Au nanostructures by layer-by-layer adsorption of poly-(ethylenimine), poly-(glycolic acid) and biotinylated poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG-biotin). Through adjusting the structure of multilayer film, an optimum interaction distance between Au nanostructures and fluorophores for the MEF effect was achieved. Meanwhile, the surface PLL-g-PEG-biotin layer allows the film to capture specific streptavidin through biotin-streptavidin interaction. Owing to the MEF effect of Au nanostructures, a significant enhancement in the fluorescence of fluorescein isothiocyanate (FITC) that labeled streptavidin was successfully obtained. This optical functional composite film with enhanced fluorescence could be used to recognize specific protein in a facile and efficient way.