Plasmon Waveguide Resonance Raman Spectroscopy

Abstract

Raman spectra were collected from a 1.25 M aqueous pyridine solution, 100-nm polystyrene film or a trimethyl(phenyl)silane monolayer at a plasmon waveguide interface under total internal reflection (TIR). The plasmon waveguide resonance (PWR) interface consisted of a sapphire prism/49 to 50 nm Au/548 to 630 nm SiO(2) and a monolayer, thin film or aqueous analyte. The Raman peak area as a function of incident angle was measured using a 785-nm excitation wavelength, and was compared to the Raman peak area obtained at a sapphire or sapphire/50 nm Au interface. In contrast to measurements at a bare sapphire prism, increased surface sensitivity and signal were obtained from the PWR interface. In contrast to measurements at a bare Au film where only p-polarized incident light generates an enhanced interfacial electric field, plasmon waveguide interfaces enable excitation with orthogonal polarizations using s- or p-polarized incident light. The Raman scatter from a monolayer was recorded at the PWR interface with a signal-to-noise ratio of 5.6 when averaging 3 accumulations with 3 min acquisition times using nonresonant excitation, whereas no signal was recorded from a monolayer at the sapphire interface. The reflected light from the interface enabled the identification of the incident angle where the maximum Raman scatter was produced, and the Raman signal generated at the plasmon waveguide interface was modeled by the enhanced interfacial mean square electric field relative to the incident field. In comparison to the techniques on which this work was based (i.e., PWR spectroscopy, TIR Raman spectroscopy at the prism interface, and surface plasmon resonance (SPR) Raman spectroscopy at the prism/Au interface), chemical specificity was added to PWR spectroscopy, a signal enhancement mechanism was introduced for TIR Raman spectroscopy, and polarization control of the interfacial electric field was added to SPR Raman spectroscopy.

Extracting interface locations in multilayer polymer waveguide films using scanning angle Raman spectroscopy

“…Similar trends are observed for sample 3-Bi ( Figure S2A) and sample 3-Tri ( Figure S3A). These representative calculated results suggest that it should be feasible to use SA Raman spectroscopy, with a signal that is proportional to the electric field intensity, [37][38][39][40]49,[53][54][55][56] to measure total film thickness as well as the location of polymer interfaces for both bilayer and trilayer films.…”

Multi-Channel Hyperspectral Fluorescence Detection Excited by Coupled Plasmon-Waveguide Resonance

“…Coupled plasmon-waveguide resonance (CPWR) offers a narrower full width half-maximum (FWHM) of the reflective curves that leads to increased precision over conventional surface plasmon resonance (SPR) sensors [14]. Meanwhile, theoretical results indicate that CPWR also results in better performance for both detection range and enhanced electromagnetic field which is highly suitable for dark field excitation of fluorescence to maintain an appreciable sensitivity and signal-to-noise ratio [15]. …”

Scanning Angle Total Internal Reflection Raman Spectroscopy of Thin Polymer Films

“…Plasmon waveguide resonance (PWR) Raman spectroscopy is a label free spectroscopic method for interfacial analysis with chemical specificity [1][2]. In a standard PWR Raman spectroscopy experiment the illuminating light is directed onto a prism/metal/dielectric/bulk interface at a specific incident angle.…”

“…Plasmon waveguides operate by coupling surface plasmon modes in the metal to guided modes within the dielectric layer or waveguide [4]. Recent work has shown that the amplified electric field at a waveguide interface can be used for generating Raman spectra with large signal-to-noise ratios for solutions, polymer films and monolayers [1][2].…”