Rational design and optimization of plasmonic nanoarrays for surface enhanced infrared spectroscopy

Abstract

We present an approach for rational design and optimization of plasmonic arrays for ultrasensitive surface enhanced infrared absorption (SEIRA) spectroscopy of specific protein analytes. Motivated by our previous work that demonstrated sub-attomole detection of surface-bound silk fibroin [Proc. Natl. Acad. Sci. U.S.A. 106, 19227 (2009)], we introduce here a general framework that allows for the numerical optimization of metamaterial sensor designs in order to maximize the absorbance signal. A critical feature of our method is the explicit compensation for the perturbative effects of the analyte's refractive index which alters the resonance frequency and line-shape of the metamaterial response, thereby leading to spectral distortion in SEIRA signatures. As an example, we leverage our method to optimize the geometry of periodic arrays of plasmonic nanoparticles on both Si and CaF2 substrates. The optimal geometries result in a three-order of magnitude absorbance enhancement compared to an unstructured Au layer, with the CaF2 substrate offering an additional factor of three enhancement in absorbance over a traditional Si substrate. The latter improvement arises from increase of near-field intensity over the Au nanobar surface for the lower index substrate. Finally, we perform sensitivity analysis for our optimized arrays to predict the effects of fabrication imperfections. We find that <20% deviation from the optimized absorbance response is readily achievable over large areas with modern nanofabrication techniques.

Periodic array-based substrates for surface-enhanced infrared spectroscopy

“…In a follow-up study of [74] from Liberman et al [75], a slightly different group around the same first author investigated an approach to further optimize diffractioncoupled plasmonic arrays for SEIRS. A general problem in the search for optimized substrates is the impossibility to scan the complete parameter space by numerical methods.…”

Engineering mid-infrared nanoantennas for surface enhanced infrared absorption spectroscopy

“…The simple intuition of increasing signal with field enhancements is the basis for surface enhanced infrared absorption (SEIRA) spectroscopy [15,16], in analogy with surface-enhanced Raman scattering (SERS) [7]. While early studies have relied on metal island films, prepared either by physical vapor deposition or chemical means [15][16][17][18], recent work has shown that nanofabricated plasmonic nanoantennas are an extremely promising approach, with a number of important advantages [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. These include improved repeatability [34,35,37], deterministic and well-defined sensing regions [19,20,24,32,[34][35][36] and dramatically higher absorption signal enhancement factors [19][20][21][22][23][25][26][27][32][33]…”

“…Specifically, due to particle sizes and geometrical fluctuations in metal island films, generally the long wavelength tail of a stochastic collection of plasmon resonances is responsible for field enhancement. In contrast, nanoantennas can be engineered to support a single, welldefined resonance directly at the frequency of interest, leading to a resonant coupling between the absorption line and the plasmonic mode [22,24,25,[27][28][29][30][31][32][33][34][35][36]39]. In this review we discuss the basic principles and key focus areas essential to moving this resonant SEIRA approach forward as a promising technique applied in various fields including biotechnology, pharmacology, biomedical research and biology to yield new insights.…”

“…In this review we discuss the basic principles and key focus areas essential to moving this resonant SEIRA approach forward as a promising technique applied in various fields including biotechnology, pharmacology, biomedical research and biology to yield new insights. While we will primarily consider our work in utilizing gold (Au) nanoantennas [24,[26][27][28][29]31,35,39,40], there are a wide range of other possibilities for controlling the interaction between mid-infrared light and a biological sample. These include other flavors of plasmonic resonances such as surface plasmon polaritons [19,20,41], alternative material systems [42][43][44] for forming nanoscale waveguides and resonators as well as integrated and fiber optics based solutions [45].…”

Mapping the sensitivity of split ring resonators using a localized analyte

“…[1][2][3][4][5] Detection of minute quantities of analytes is of great interest for immunosensing, diagnostics, security, and forensic applications. [1][2][3][4][5] Localized surface plasmon resonances (LSPRs) are collective oscillations of conduction electrons that are produced in metallic nanostructures when excited by incident light. The localization of surface plasmons allows for the concentration of light in extremely small modal volumes ($10 to 10 3 nm 3 ) that form electromagnetic hot-spots.…”