Exploring Plasmonic Refractive Index Nanosensors with Different Applications

Abstract

In this thesis, three high-yielding plasmonic refractive index sensors based on Metal- Insulator-Metal waveguide are proposed to satisfy the current sensing demands in different sectors, for example, medical, forensic, and industrial. The proposed works employ a straight waveguide and different resonators, such as ring resonator, concentric double-ring resonator, and cavity resonator in the two-dimensional form to expedite the simulations. COMSOL Multiphysics is chosen as the wave-solver, which inherently deploys the Finite Element Method. The re-simulations of existing structures corroborate the computational accuracy of COMSOL Multiphysics. Furthermore, all three designed sensors fabricated through nanoimprint lithography technique exhibit linear correlation with the refractive index and the resonant wavelength. This linear relationship is exploited to sense the unknown materials. Moreover, the structural parameters of the plasmonic sensors are sensitive to variations. Thus, the suggested sensors undergo extensive simulations and optimization processes to maximize their performance. The proposed first work with the concentric double-ring resonator exhibit an initial sensitivity of 1804.23 nm/RIU. A maximum sensitivity of 3522.44 nm/RIU is obtained after optimization. Additionally, the optimized FOM, FOM*, Q-factor, detection limit of the illustrated sensor with CDRR are 80.07, 0.73 106, 83.65, 2.37 10-7 RIU, respectively. This proposed work is deployed to detect cancerous cells, sense chemical concentrations, perform plasmonic filtering, and display superior performance in all three cases. The proposed second work with ring resonator initially displays a sensitivity of 2763.75 nm/RIU. After extensive simulations, a final sensitivity of 3573.3 nm/RIU is obtained. The tolerance capability of the structure is studied by introducing nano slits on the rings and demonstrates 0.63% and 1.12% reduction in sensitivity. The device has also been exploited for the label-free detection of DNA hybridization and other biomolecules, such as plasma and hemoglobin with high accuracy and reliability. The proposed third work with six cavity resonators can detect six primary colors in the visible wavelength. An initial sensitivity of 648.41 nm/RIU and FOM of 141.29 are found based on the transmittance profile. The structural parameters are optimized to maximize the performance of the modeled device both as a color filter and a refractive index sensor. The optimized FOM, FOM* and sensitivity are recorded as 218.80, 4.771 104, and 865.31 nm/RIU, respectively. Therefore, the multi-purpose functionalities of the proposed nanosensors make them emerging contenders for state-of-the-art lab-on-a-chip tasks