Abstract
A surface plasmon resonance sensing and imaging platform based on plasmonic non-uniform nano-gratings with narrow groove (sub-10 nm) is presented. In these nanogratings, normally incident optical radiation is directly coupled to surface plasmons without the requirements of any other conventional surface plasmon coupling mechanisms such as prism-based or grating-based coupling. Theoretical analysis of practically realizable plasmonic non-uniform nano-gratings with rounded tops and slanted sidewalls is carried out to numerically to determine reflectance and differential reflectance signals when the localized refractive index of the medium around the gold layer present in these nano-gratings is changed. This change in the localized refractive index can occur due to the binding of biomolecules to the gold layer. Two kinds of plasmonic non-uniform nano-gratings are studied using finite difference time domain (FDTD) modelling: gold nano-gratings (GNGs) and gold-coated silicon nano-gratings (GSNGs). The plasmonic non-uniform nano-gratings being proposed, more specifically the GSNGs, can be easily fabricated with the presently existing nanofabrication and thin film deposition methods as opposed to uniform nano-gratings (with parallel sidewalls) that are very difficult to fabricate. The plasmonic non-uniform nano-gratings with narrow grooves eliminate the strict requirements on the angle of incidence for coupling of light into surface plasmons, which are needed in conventional prism-based coupling mechanisms. By employing FDTD calculations, we demonstrate that these plasmonic non-uniform nano-gratings provide very high differential reflectance amplitude values, which are indicative of high sensitivities of the SPR or SPRi sensors when the localized refractive index around the sensors is varied. Moreover, the sensors being proposed in this article provide a maximum sensitivity of localized refractive index sensing (i.e. surface sensitivity or $\text{S}_{\mathrm {S}}$ ) of 70 nm/nm with a figure of merit of the localized sensor (FOMS) of 1.5 nm $^{-1}$ . This sensitivity of localized refractive index sensing is the highest reported thus far in comparison with previously reported plasmonic sensors. Moreover, these plasmonic non-uniform nano-grating based sensors exhibit significantly better performance when compared with conventional SPR or SPRi sensors based on the Kretschmann configuration.
Highlights
Surface plasmons are collective oscillations of conduction electrons at the interface of a metal and a dielectric [1,2,3,4,5,6,7]
The sensors being proposed in this paper provide a maximum sensitivity of localized refractive index sensing of 70 nm/nm with a figure of merit of the localized sensor (FOMS) of 1.5 nm-1
We demonstrate the applicability of these nonuniform narrow groove nano-gratings for highly sensitive detection of localized changes of refractive index at the nano-grating surface
Summary
Surface plasmons are collective oscillations of conduction electrons at the interface of a metal and a dielectric [1,2,3,4,5,6,7]. SPR and LSPR diagnostic techniques have dominated the current state-of-the-art technology for providing highly reliable and sensitive detection of analytes with enhanced specificity These label-free techniques are being extensively employed by researchers working in the field of biosensors due to their distinct advantage over the conventional labelling assays, as a label may damage or altogether modify the chemical structure of the molecular affinity binding electrons. The nano-gratings modelled in our work can be employed for reliable and sensitive detection of localized fluctuations in refractive index resulting from biomolecular interactions of target analytes with the nano-grating metallic surface, making these structures an ideal platform for SPR and SPRi based sensing
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
