Fluorescence Enhancement of Rhodamine B in the Presence of Photonic Crystal Heterostructures

Photonic crystal heterostructures have been obtained by mixing a styrene-hydroxyethylmethacrylate (ST-HEMA) colloidal dispersion with Au colloidal solution (1:5 volume ration). To modify the heterogeneous photonic crystal with Rh, the first step has been the chemical attachment of HO-R-SH to the surface of Au particles. The next reaction was the esterification of hydroxyl modified photonic crystal with Rh. In UV-vis spectra the peak at 600 nm is possible due to the Bragg diffraction of dye molecule aggregates. In the case of ST-HEMA-Au-SH-Rh, the same signal has been shifted to 625 nm, induced by the existence of preformed particles. A decrease in the reflection response of Rh is noticed, and this corresponds to the absorption domain of dye, namely, the Q-band. The large decrease in area for particles ST-HEMA-Au-SH-Rh could be attributed to the overlapping of the Rh reflection band with the photonic crystal stop band. In the case of fluorescence, to the same excitation wavelength, for the ST-HEMA-Au-SH-Rh film, the emissions have been amplified compared with the signal of Rh film. A preliminary test has been performed for putting into evidence the chemosensor properties of ST-HEMA-Au-SH-Rh film modified with triethylenetetramine.