title: Fluorescence Spectroscopy with Metal-Dielectric Waveguides.
abstract: We describe a hybrid metal-dielectric waveguide structures (MDWs) with numerous potential applications in the biosciences. These structures consist of a thin metal film coated with a dielectric layer. Depending on the thickness of the dielectric layer, the modes can be localized near the metal, within the dielectric, or at the top surface of the dielectric. The optical modes in a metal-dielectric waveguide can have either S (TE) or P (TM) polarization. The dielectric spacer avoids the quenching, which usually occurs for fluorophores within about 5 nm from the metal. Additionally, the resonances display a sharp angular dependence and can exhibit several hundred-fold increases in intensity (E2) at the silica-air interface relative to the incident intensity. Fluorophores placed on top of the silica layer couple efficiently with the metal, resulting in a sharp angular distribution of emission through the metal and down from the bottom of the structure. This coupling occurs over large distances to several hundred nm away from the metal and was found to be consistent with simulations of the reflectivity of the metal-dielectric waveguides. Remarkably, for some silica thicknesses, the emission is almost completely coupled through the structure with little free-space emission away from the metal-dielectric waveguide. The efficiency of fluorophore coupling is related to the quality of the resonant modes sustained by the metal-dielectric waveguide, resulting in coupling of most of the emission through the metal into the underlying glass substrates. Metal-dielectric waveguides also provide a method to resolve the emission from surface-bound fluorophores from the bulk-phase fluorophores. Metal-dielectric waveguides are simple to fabricate for large surface areas, the resonance wavelength can be adjusted by the dielectric thickness, and the silica surface is suitable for coupling to biomolecules. Metal-dielectric waveguides can have numerous applications in diagnostics and high-throughput proteomics or DNA analysis.
authors.affiliation: Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 W. Lombard St., Baltimore, MD 21201, USA.
authors.forename: Ramachandram
authors.initials: R
authors.lastname: Badugu
authors.affiliation: Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 W. Lombard St., Baltimore, MD 21201, USA.
authors.forename: Henryk
authors.initials: H
authors.lastname: Szmacinski
authors.affiliation: Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 W. Lombard St., Baltimore, MD 21201, USA.
authors.forename: Krishanu
authors.initials: K
authors.lastname: Ray
authors.affiliation: Department of Applied Science and Technology, Polytechnic University of Turin, Corso Duca degli Abruzzi 24, 10129 Turin, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Descrovi
authors.affiliation: Department of Applied Science and Technology, Polytechnic University of Turin, Corso Duca degli Abruzzi 24, 10129 Turin, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Ricciardi
authors.affiliation: Institute of Photonics, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Douguo
authors.initials: D
authors.lastname: Zhang
authors.affiliation: School of Science, Southwest University of Science and Technology, Mianyang, Sichuan 621010, China.
authors.forename: Junxue
authors.initials: J
authors.lastname: Chen
authors.affiliation: School of Physics and Information Technology, Shaanxi Normal University, Xi'an, 710062 China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Huo
authors.affiliation: Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 W. Lombard St., Baltimore, MD 21201, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Lakowicz
keywords: Plasmon coupled waveguide; Plasmon-controlled fluorescence; Surface plasmon-coupled emission; Surface plasmon-enhanced fluorescence; Total internal reflection; Waveguide-coupled emission