Angle-Tunable Enhanced Infrared Reflection Absorption Spectroscopy via Grating-Coupled Surface Plasmon Resonance

Abstract

Surface enhanced infrared absorption (SEIRA) spectroscopy is an attractive method for increasing the prominence of vibrational modes in infrared spectroscopy. To date, the majority of reports associated with SEIRA utilize localized surface plasmon resonance from metal nanoparticles to enhance electromagnetic fields in the region of analytes. Limited work has been performed using propagating surface plasmons as a method for SEIRA excitation. In this report, we demonstrate angle-tunable enhancement of vibrational stretching modes associated with a thin poly(methyl methacrylate) (PMMA) film that is coupled to a silvercoated diffraction grating. Gratings are fabricated using laser interference lithography to achieve precise surface periodicities, which can be used to generate surface plasmons that overlap with specific vibrational modes in the polymer film. Infrared reflection absorption spectra are presented for both bare silver and PMMA-coated silver gratings at a range of angles and polarization states. In addition, spectra were obtained with the grating direction oriented perpendicular and parallel to the infrared source in order to isolate plasmon enhancement effects. Optical simulations using the rigorous coupled-wave analysis method were used to identify the origin of the plasmon-induced enhancement. Angle-dependent absorption measurements achieved signal enhancements of more than 10-times the signal in the absence of the plasmon. ABSTRACT: Surface enhanced infrared absorption (SEIRA) spectroscopy is an attractive method for increasing the prominence of vibrational modes in infrared spectroscopy. To date, the majority of reports associated with SEIRA utilize localized surface plasmon resonance from metal nanoparticles to enhance electromagnetic fields in the region of analytes. Limited work has been performed using propagating surface plasmons as a method for SEIRA excitation. In this report, we demonstrate angle-tunable enhancement of vibrational stretching modes associated with a thin poly(methyl methacrylate) (PMMA) film that is coupled to a silver-coated diffraction grating. Gratings are fabricated using laser interference lithography to achieve precise surface periodicities, which can be used to generate surface plasmons that overlap with specific vibrational modes in the polymer film. Infrared reflection absorption spectra are presented for both bare silver and PMMA-coated silver gratings at a range of angles and polarization states. In addition, spectra were obtained with the grating direction oriented perpendicular and parallel to the infrared source in order to isolate plasmon enhancement effects. Optical simulations using the rigorous coupled-wave analysis method were used to identify the origin of the plasmon-induced enhancement. Angle-dependent absorption measurements achieved signal enhancements of more than 10-times the signal in the absence of the plasmon. Disciplines Biological Engineering | Chemical EngineeringS urface plasmon resonance (SPR) is well established as a

Periodic array-based substrates for surface-enhanced infrared spectroscopy

“…Even thicker PMMA films with thicknesses between 30 and 300 nm were used in the work of Petefish and Hillier to reveal the SEIRS characteristics of a grating fabricated by laser interference lithography [94] (see Figure 7B). As a result, these gratings, subsequently covered with silver, show a sinusoidal surface profile with a maximum height of 100 nm (3025 nm pitch) and 300 nm (1710 nm pitch).…”

“…The authors found by calculation that a reflectance signal of more than 5% should be possible if a maximum imaginary dielectric permittivity of 3 at the molecular resonance was assumed. For the assumed thickness of 1 nm, this would be an enormous signal, but the simulation does not take into account that the strongest imaginary dielectric permittivity for an organic material in the infrared spectral range (caused by the C = O stretching vibration) is not higher than about 1.5 [94]. For proteins, it seems that the corresponding vibrations that involve the C = O stretching vibrations (amide I and II) are even weaker and do not show values above 1 [144].…”

Molecular detection by active Fano‐sensor

“…The second issue is related to the dynamical tunability of the PFR. It is known that if the vibrational modes of the molecules is far away from a plasmonic resonance, the signal from the molecular vibrational absorption (relating with the absorption cross section) will be significantly decreased . Therefore, the resonant wavelength of nanostructure has to be tuned.…”

Exploration of grating-based surface plasmon resonance systems for wave vector matching to enhance plasmon modes and preliminary surface plasmon-enhanced fluorescence interrogation

“…This RI sensitivity allows for high throughput label free sensing/diagnostics [26][27][28][29][30][31] and thin film deposition tracking. [32][33][34][35][36][37][38][39][40] Additionally, because SPR peak shift can be tracked versus time, kinetics and binding affinity can be elucidated. 19,41,42 The first commercial SPR instrument for binding affinity was sold in 1990 under the name of BIACORE.…”

“…Additionally, the enhanced electric field associated with the resonance mode can be matched to atomic or molecular resonance Spectroscopic techniques enhanced by SPR include Surface Enhanced Raman Spectroscopy (SERS), 34,[46][47][48][49][50] Surface Enhanced Infrared Absorption (SEIRA), 36,47,51,52 and SPR enhanced fluorescent signaling. [53][54][55][56][57][58][59][60][61] SPR also plays an integral role in near-field imaging techniques.…”