Fan-Shaped Gold Nanoantennas above Reflective Substrates for Surface-Enhanced Infrared Absorption (SEIRA)

Abstract

Here, we report a new nanoantenna for surface-enhanced infrared absorption (SEIRA) detection, consisting of a fan-shaped Au structure positioned at a well-specified distance above a reflective plane with an intervening silica spacer layer. We examine how to optimize both the antenna dimensions and the spacer layer for optimal SEIRA enhancement of the C-H stretching mode. This tunable 3D geometry yields a theoretical SEIRA enhancement factor of 10(5), corresponding to the experimental detection of 20-200 zeptomoles of octadecanethiol, using a standard commercial FTIR spectrometer. Experimental studies illustrate the sensitivity of the observed SEIRA signal to the gap dimensions. The optimized antenna structure exhibits an order of magnitude greater SEIRA sensitivity than previous record-setting designs.

Versatile Direct Laser Writing Lithography Technique for Surface Enhanced Infrared Spectroscopy Sensors

“…Two notable examples for such detection methods are surface enhanced Raman scattering (SERS) 1-4 , and surface enhanced infrared absorption (SEIRA) [4][5][6][7][8][9][10][11][12][13][14][15][16] . In SEIRA spectroscopy, metallic and dielectric nanoantennas that exhibit plasmonic resonances in the Infra-Red (IR) regime are used to intensify the IR absorption signal of known vibrational modes of molecules, so that even small amount of analytes can be identified [4][5][6][7][8][9][10][11][12][13][14][15][16] . The improved detection originates from the excitation of localized surface plasmon resonances (LSPRs) -charge oscillations on the surface of the nano-structured surface -which give rise to a strong local electric field at the vicinity of the nanostructures and enhanced coupling between the textured surface and the vibrational modes of the adsorbed molecules.…”

“…Compared to the fabrication methods listed above, like EBL, DLW benefits from practically ultimate freedom in the positioning and the design of the shape of the nano-structures: it obviates the need for manufacturing of pre-defined masks (which are required for stencil lithography and UV photolithography), and the resulted nano-structures are independent of the size of the spheres as in the case of colloidal and spherical-lens lithography. With recently emerged new designs of SEIRA nano-structures which depart from simple bar-shaped antennas, the introduction of a flexible and fast fabrication method that can serve as an alternative to EBL is of great interest 13,14,[17][18][19] . In this work we report the fabrication and testing of SEIRA chemical sensor based on an alternative approach for using TPP-DLW to fabricate large arrays of nano-structures.…”

Periodic array-based substrates for surface-enhanced infrared spectroscopy

“…Most nanoantennas are investigated with these conditions. However, nanoantennas usually have surfaces oriented perpendicular to the interface of the substrate on which they are placed, and those are often the ones generating the hotspots and contributing most strongly to the SEIRS signals, which could serve as an argument to use IRRAS experiments with angles of incidence >60° as reference experiments [56].…”

Generalized theoretical method for the interaction between arbitrary nonuniform electric field and molecular vibrations: Toward near-field infrared spectroscopy and microscopy

“…We consider that the use of the dipole radiation would be appropriate when the tip-molecule distance is larger than the tip radius, (∼10 nm), because the computed fields around a conical tip look like the dipole field. 24,57 Actual comparisons will be made in the future study after combining the computational electrodynamics with the present methods using geometrically realistic metal tips. This near-field is used to calculate the effective electric field by substituting the E in Eq.…”