Dispersion-based intertwined SEIRA and SPR effect detection of 2,4-dinitrotoluene using a plasmonic metasurface

Abstract

Surface enhanced infrared absorption (SEIRA) spectroscopy and surface plasmon resonance (SPR) make possible, thanks to plasmonics nanoantennas, the detection of low quantities of biological and chemical materials. Here, we investigate the infrared response of 2,4-dinitrotoluene deposited on various arrays of closely arranged metal-insulator-metal (MIM) resonators and experimentally show how the natural dispersion of the complex refractive index leads to an intertwined combination of SEIRA and SPR effect that can be leveraged to identify molecules. They are shown to be efficient for SEIRA spectroscopy and allows detecting of the dispersive explosive material, 2,4-dinitrotoluene. By changing the in-plane parameters, a whole spectral range of absorptions of 2,4-DNT is scanned. These results open the way to the design of sensors based on SEIRA and SPR combined effects, without including a spectrometer.

Helmholtz Resonator Applied to Nanocrystal-Based Infrared Sensing

“…On the other hand, the nanofabrication of the structure depicted in Figure 1b is challenging, requiring a simplified version. 33 Here, we demonstrate that the main properties of the initial Helmholtz resonator can be preserved in a simplified version of it, see Figure 1c and S1. For a full comparison of the traditional and simplified geometry of Helmholtz, see the discussion associated with Figures S5−S8.…”

“…This resonator presents several advantages, such as minimizing the volume of the optically active area (i.e., the gap opening) and being poorly dispersive (i.e., robust toward the incident angle, which is of the utmost interest for integration into focal plane arrays). On the other hand, the nanofabrication of the structure depicted in Figure b is challenging, requiring a simplified version . Here, we demonstrate that the main properties of the initial Helmholtz resonator can be preserved in a simplified version of it, see Figure c and S1.…”

Over-coupled resonator for broadband surface enhanced infrared absorption (SEIRA)

“…Usually, SEIRA effect is quantified with post-treatment, using for instance smoothing algorithm or artificial materials to decouple SEIRA from SPR effect. 13,29 Noteworthily, in the over-coupled configuration, the SPR effect is not plaguing the analysis and the reflectivity difference ∆R = R withoutP M M A − R withP M M A can be directly used to identify and quantify the chemical species. The reflectivity difference is plotted in Fig.…”

“…3 The development of optical nanores-onators with localized hot spots has enabled SEIRA sensors with improved perfomances. [4][5][6][7][8][9][10][11][12][13][14][15] They have been applied to the detection of species for biosensing, 7,14-21 environmental monitoring with gas sensing [22][23][24] or to other domains linked to industrial control, 25 or defense applications. 13 All the previous works are based on the same paradigm: IR absorption can be enhanced by first enhancing the incident field using a resonator and then inserting the analyte assuming that its presence will not perturb the resonator.…”

“…The resonator is composed of a dielectric cavity surmounted by a metallic layer, structured with a periodic array of slits where the electric field is highly confined at resonance. This type of structure has been previously studied by Fabas et al 13 Here, the dielectric layer is taken to be zinc sulfide (ZnS), which has the advantage of being transparent in the midinfrared. As shown in the Supporting Information, the electric field intensity is enhanced in the volume of the slit at resonance by a factor of 300.…”