Nanocomposites and nanomaterials
Enhanced fluorescence in the system “polymer matrix-dye-high-conductive nanostructure arrays”
Lytvyn V.K., Lopatynskyi A.M. and Chegel V.I.
V.E. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, 41, prospect Nauky, 03028 Kyiv, Ukraine
E-mail: lytvet@ukr.net
Many research studies reported on the phenomenon of plasmon-enhanced fluorescence (PEF), which is induced by localized surface plasmon resonance (LSPR) that appears in high-conductive metal nanostructures and can significantly increase the emission of fluorophore [1]. A number of active structures have been developed for PEF, primarily based on silver and gold island films and ordered noble metal nanoparticle arrays [2,3].
In this work the special system consist of a glass substrate, high conductive nanostructure arrays coated with a SiO2 layer and a matrix "polymer-fluorophore" was developed to enhance the fluorescence signal (Fig. 1). Polymer allows to increase the number of fluorophore molecules that get into the evanescent electromagnetic field of localized plasmon. This, in turn, leads to the increasing of the radiative decay rate of the "nanoparticle-fluorophore" system.

Fig.1. System “polymer matrix with embeded dye-SiO2-high-conductive nanostructure arrays” for PEF studies.

To estimate the possibilities of developed system for PEF studies the fluorescence of Rhodamine 6G (R6G) near silver and gold nanostructure arrays (SNA and GNA, respectively) with dielectric coating of silicon dioxide with different thicknesses - 10, 15, 20 and 25 nm was studied. SNA and GNA with SiO2 were dipped in the composite, consists of an aqueous solution of R6G and polyacrylic acid (PAA), then slowly removed (5 mm/min) and dried. The thickness of polymer composite was about 2 microns (according to AFM). The concentration of R6G in the polymer matrix was 10-5 mol / L. The samples were irradiated with a green laser (532 nm) and fluorescence spectra of R6G were measured. The results are shown that for all samples enhancement of  R6G fluorescence near SNA and GNA compared with the level of fluorescence signal on bare glass was observed. The maximum enhancement of  R6G fluorescence was obtained for the samples with dielectric layer thickness about 20 nm, for SNA – about 10 nm, and dependence of the enhancement factor exhibits the bell-shaped character. Enhancement factor defined as the ratio of fluorescence intensity of the dye near coated SNA and GNA to the intensity of fluorescence of dye on the bare glass.
Our results allow implementing the fluorescence signal manipulation technique using LSPR phenomenon by controlling the different parameters of nanostructure arrays, type of the polymer and thickness of dielectric coating.

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