Surface enhanced infrared absorption spectroscopy based on gold nanostars and spherical nanoparticles

Abstract

Plasmonic anisotropic nanoparticles possess a number of hot spots on their surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the nanostructures. In this paper, we explore different plasmonic nanostructures, including anisotropic gold nanostars (AuNSts) and spherical gold nanoparticles, in surface-enhanced infrared absorption spectroscopy (SEIRAS) in an attenuated total reflection (ATR) configuration. In our experiments, we observed up to 10-times enhancement of the infrared (IR) absorption of thioglycolic acid (TGA) and up to 2-times enhancement of signals for bovine serum albumin (BSA) protein on plasmonic nanostructure-based films deposited on a silicon (Si) internal reflection element (IRE) compared to bare Si IRE. The dependence of the observed enhancement on the amount of AuNSts present at the surface of the IRE has been demonstrated. Quantitative studies with both, TGA and BSA were performed, observing that the SEIRA signal can be correlated to the concentration of analyte molecules present within the evanescent field. The calibration curves in the presence of the AuNSts showed enhanced sensitivity as compared with the bare Si IRE. We finally compare efficiencies of anisotropic AuNSts and spherical citrate-capped and "bare" laser-synthesized gold nanoparticles as SEIRAS substrates for the detection of TGA and BSA. The signal obtained from AuNSts was at least 2 times higher for TGA molecules in comparison with spherical gold nanoparticles, which was explained by a more efficient generation of hot spots on anisotropic surface due to the presence of sharp edges, tips or vertices, leading to a high electric field strength surrounding the AuNSts.

Surface-Enhanced Absorption Spectroscopy for Optical Fiber Sensing

“…The results are comparable to some observations of non-resonant SEIRAS in the Kretschmann configuration [39], but the enhancement is lower than other demonstrations in the infrared range [9,13]. This could be attributed to the fact that there is plasmon interaction on only part of the circumference of the taper.…”

“…The size, shape, and pattern of the metal particles in an LSPR design determine the resonance wavelengths and the strength and shape of the electrical field [30]. LSPR is used to tailor the plasmon resonance wavelength to the application [12,13]. For SEIRAS, islands or quasi-films have typically provided better signal enhancement than a metal film [3,10,30].…”

“…The plasmon-molecule interaction may also be exploited to enhance the absorption signal in classical absorption spectroscopy. First, shown by Hartstein [9], surface-enhanced infrared absorption spectroscopy (SEIRAS) utilizes metal nanostructures to produce an enhancement effect for infrared spectroscopy; several subsequent works have investigated this effect with a focus on tailoring the resonance wavelength with different nanostructures and antennas [10][11][12][13]. More recently, Fano resonances were discovered and explained with respect to narrow molecular vibrations [14].…”

“…Some works have demonstrated the importance of the film/semi-film growth parameters, such as thickness and deposition rate, for the plasmon characteristics [15,16]. However, the effect of SEIRAS has mostly been shown in lab conditions that are not easily adapted to optical fibers using the Kretschmann configuration with a prism or using an ATR probe [9,10,13,15]. For practical applicability, we here implement the enhancement directly on an optical fiber.…”

Gallium arsenide waveguides as a platform for direct mid-infrared vibrational spectroscopy

“…4 vs. the non-enhanced counterpart. This enhancement factor is similar to previously reported enhancement factors for biomolecules [49]. This enhancement factor is clearly at the lower range of possible SEIRA enhancement factors reported in literature, where enhancement factors up to 1000 have been shown [50].…”