title: Distance-dependent metal-enhanced fluorescence from Langmuir-Blodgett monolayers of alkyl-NBD derivatives on silver island films.
abstract: We described the effect of fluorophore distance from the silver island films (SIFs) on the metal-enhanced fluorescence (MEF) from two newly developed long-chain nitrobenzoxadiazole derivatives (NBD-C16 and NBD-C18). The well-established Langmuir-Blodgett technique is used to deposit the fluorophores at defined distances from the SIFs surface, and an inert amphiphilic stearic acid is used to control the distance. NBD probes deposited directly on the SIFs surface show the highest metal-enhanced fluorescence of approximately 32-fold, and both of the probes that were studied show a consistent decrease in metal-enhanced fluorescence when increasing the distance from the fluorophore to the SIFs surface. The lowest fluorescence enhancement of approximately 4-fold is observed for the probes located 90 nm from the SIFs surface. Additionally, we also have noticed the shortest fluorescence lifetimes for the NBD probes deposited directly onto the SIFs surface, and the lifetimes are consistently increased when increasing the distances between the fluorophore and SIFs surfaces. These contrasting spectral changes, enhanced fluorescence, and decreased fluorescence lifetimes are in accordance with an increase in the rate of radiative decay for fluorophores near the silver particles. The present study provides significant information on the effect of fluorophore distance on the metal-enhanced fluorescence phenomenon.
authors.affiliation: Center for Fluorescence Spectroscopy, University of Maryland School of Medicine, Department of Biochemistry and Molecular Biology, 725 West Lombard Street, Baltimore, Maryland 21201, USA.
authors.forename: Krishanu
authors.initials: K
authors.lastname: Ray
authors.forename: Ramachandram
authors.initials: R
authors.lastname: Badugu
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Lakowicz
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000737:chemistry*; D008567:Membranes, Artificial; D012834:Silver / Q000737:chemistry*; D013229:Stearic Acids / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D008567:Membranes, Artificial; D013229:Stearic Acids; D012834:Silver; C031183:stearic acid; D009327:4-Chloro-7-nitrobenzofurazan