Experimental demonstration of a novel bio‑sensing platform via plasmonic band gap formation in gold nano‑patch arrays

Abstract

In this paper we discuss the possibility of implementing a novel bio-sensing platform based on the observation of the shift of the leaky surface plasmon mode that occurs at the edge of the plasmonic band gap of metal gratings, when an analyte is deposited on top of the metallic structure. We report numerical calculations, fabrication and experimental measurements to prove the sensing capability of a two-dimensional array of gold nano-patches in the detection of a small quantity of Isopropyl Alcohol (IPA) deposited on top of sensor surface. The calculated sensitivity of our device approaches a value of 1000 nm/RIU with a corresponding Figure of Merit (FOM) of 222 RIU(-1). The presence of IPA can also be visually estimated by observing a color variation in the diffracted field. We show that color brightness and intensity variations can be ascribed to a change in the aperture size, keeping the periodicity constant, and to different types of analyte deposited on the sample, respectively. Moreover, we demonstrate that unavoidable fabrication imperfections revealed by the presence of rounded corners and surface roughness do not significantly affect device performance.

Graphene assisted nanostructures

“…Figure 1 shows the sketch of the proposed 2D periodic arrangement of graphene monolayer antidots that can exhibit different shapes. It is important to remark that, in the visible range, these 2D structures can support three different resonances when illuminated by a Transverse Magnetic (TM) polarized field, as previously reported [15][16][17]: a) a narrow band resonant state involving the whole grating (state V); b) a leaky mode due to the coupling between a SPP and the impinging light (state M); and c) a broadband Fabry-Perot-like resonance due to the transverse-electro-magnetic TEM guided mode generated in the slit, which acts as a metal-insulator-metal (MIM) waveguide (state H). In this work, the thickness of the graphene is not sufficient to excite the FabryPerot-like resonance and, hence, there is only one plasmonic resonance due to the periodic arrangement.…”

Experimental demonstration of plasmonic-grating-assisted optical biosensor

“…The full-width at half-maximum (FWHM) of the high-energy band-edge state is ~5 nm at normal incidence, and it retains the same spectral width even for larger incident angles. Moreover, for this particular resonant state the magnetic field embraces the entire grating, with a field enhancement up to 25 times larger than the incoming field [30,31]. Although the presence of the silicon substrate introduces resonances related to the silicon/metal interface, the plasmonic band gap associated with the Si/metal interface is not visible in the spectra reported in Figure 2 because it occurs at much longer wavelengths, while higher order plasmonic gaps associated with this interface are not visible in the range of interest because of the absorption of silicon in the frequency range below 500 nm.…”

“…Figure 5 shows measured and calculated diffraction spectra, respectively solid and dashed red lines, for the structure with IPA solution on top: in this case the theoretical and experimental results almost completely overlap. Such shift can be also monitored through color change observation [30,32].…”

Emission and Transmission Properties of a Doubly Resonant 3D Nanodisk Yagi–Uda Antenna for Wireless Optical Communications

“…In the last years, intense efforts have been devoted to the development of the concept of antenna at the optical frequencies and the increasing interest in such devices is justified by their optical properties of strong enhancement and excellent near-field confinement [3], which ensure high standard of efficiency in applications including spectroscopy [4,5], light localization [6], heat transfer [7], photodetection [8,9], photovoltaics [10][11][12], and bio-sensing [13,14].…”