Surface enhanced fluorescence and imaging with plasmon near-fields in gold corrugated gratings

摘要

Surface plasmon-assisted fluorescence and imaging from Rhodamine 6G dye molecules in polymethyl methacrylate (PMMA) thin films deposited on gold-coated corrugated gratings of various periodicities fabricated by laser interference lithography were investigated. The fluorescence enhancement depends significantly on the periodicity of the corrugated gratings for the green light excitation centered at 548 nm with maximum enhancements at 500 and 1000 nm grating periods. A dielectric PMMA spacer layer placed between the fluorophore layer and the metal surface resulted in a further three-fold enhancement of fluorescence. The period dependent enhancement is caused by the efficient coupling of the excitation radiation to the gold gratings due to the resonant excitation of propagating surface plasmons, which assist the excitation of the fluorophores. Fluorescence imaging shows that the emitted signal is stronger from the top of the corrugated grating surface rather than from that of the valleys. It was ascertained, through surface plasmon resonant dispersion measurements and electromagnetic computations, that enhanced absorption of excitation light through propagating plasmon resonances is the prime contributor to the enhanced fluorescence.