title: Coherent anti-Stokes Raman scattering with single-molecule sensitivity using a plasmonic Fano resonance.
abstract: Plasmonic nanostructures are of particular interest as substrates for the spectroscopic detection and identification of individual molecules. Single-molecule sensitivity Raman detection has been achieved by combining resonant molecular excitation with large electromagnetic field enhancements experienced by a molecule associated with an interparticle junction. Detection of molecules with extremely small Raman cross-sections (~10(-30) cm(2) sr(-1)), however, has remained elusive. Here we show that coherent anti-Stokes Raman spectroscopy (CARS), a nonlinear spectroscopy of great utility and potential for molecular sensing, can be used to obtain single-molecule detection sensitivity, by exploiting the unique light harvesting properties of plasmonic Fano resonances. The CARS signal is enhanced by ~11 orders of magnitude relative to spontaneous Raman scattering, enabling the detection of single molecules, which is verified using a statistically rigorous bi-analyte method. This approach combines unprecedented single-molecule spectral sensitivity with plasmonic substrates that can be fabricated using top-down lithographic strategies.
authors.affiliation: 1] Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA [2] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: 1] Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA [2] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA.
authors.forename: Yu-Rong
authors.initials: YR
authors.lastname: Zhen
authors.affiliation: 1] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA [2] Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Oara
authors.initials: O
authors.lastname: Neumann
authors.affiliation: 1] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA [2] Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Jared K
authors.initials: JK
authors.lastname: Day
authors.affiliation: 1] Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA [2] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA [3] Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Nordlander
authors.affiliation: 1] Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA [2] Laboratory for Nanophotonics, Rice University, Houston, Texas 77005, USA [3] Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA.
authors.forename: Naomi J
authors.initials: NJ
authors.lastname: Halas