LiF-Ag-Si-TMDs based long-range SPR sensor in visible and NIR spectrum

Abstract

Four types of sensor structures are considered in this study: S1 (prism/Ag/SM), S2 (prism/LiF/Ag/SM), S3 (prism/LiF/Ag/Si/SM), and S4 (prism/LiF/Ag/Si/TMDs/SM), at six different wavelengths, i.e., 400, 500, 633, 785, 980 and 1024 nm. Beam width, angular sensitivity (Sang), imaging sensitivity (Simg), angular Figure-of-Merit (FoMang), imaging FoM (FoMimg), and penetration depth (PD) are calculated for comparative analysis of performance of the proposed sensor (S4). It is found that all the performance parameters except Sang. for S2, S3, and S4 are better than S1 at all the considered wavelengths. PD increases with wavelength for all the structures. FoMimg. is highest at 633 nm wavelength for all the structures except S1, whereas Simg. is highest at 633 nm wavelength for all the structures except S1 and S4 with WSe2. Highest Simg. and highest FoMimg. are 12985 RIU−1 and 1298500 (⁰RIU)−1 for S3. On comparing the structures with different TMDs, it is found that highest Simg. (7884.7 RIU−1) and highest FoMimg. (788471 (⁰RIU)−1) are obtained for S4 with WS2. Finally, it is seen that inclusion of LiF increases the imaging performance parameters, Simg. and FoMimg. at all wavelengths, which are further improved by the inclusion of Si (at 633 nm and 785 nm wavelengths). But, inclusion of TMDs over Si degrades the performance. However, TMDs are essential to increase the selective immobilization of biomolecular recognition element or affinity layer on its surface which is required for specific detection of target molecules. Therefore, effects of inclusion of TMDs on the sensor performance are also analysed.