Highly Sensitive Refractive Index Nano Sensors with Applications in Glucose Level Detection, and Gas Sensing

Abstract

This thesis investigates the design, simulation, and performance evaluation of two distinct structures for highly sensitive refractive index sensors based on Metal-Insulator-Metal (MIM) waveguides. The first structure consists of a semi-circular ring with a baffle, while the second structure incorporates double concentric semi-circular rings. Both sensors utilize specifically designed cavities to hold the material under sensing (MUS), with silver filling the surrounding area. The Finite Element Method (FEM) implemented in COMSOL Multiphysics enables numerical analysis of the proposed models and demonstrates the linear relationship between the refractive index and the corresponding shift in the resonant wavelength. In the first structure, extensive simulations and parameter optimization are performed to achieve maximum sensitivity. By tuning the structural parameters, including Lr, Wc, G, and D, to optimized values of 440 nm, 29 nm, 25 nm, and 20 nm respectively, the sensor achieves a remarkable maximum sensitivity of 4859 nm/RIU within the refractive index range of 1.5 to 1.6. Furthermore, the sensor exhibits a high sensitivity of 4255 nm/RIU when detecting different concentrations of glucose solutions. These results establish the sensor's potential for on-chip bio-sensing and chemical applications due to its exceptional sensitivity, straightforward architecture, cost-efficiency, and promising performance as a glucometer. Building upon the success of the first structure, the second structure with double concentric semi-circular rings is developed. By carefully designing the structural parameters, such as the outer semicircle diameter (Lr) at 399 nm, waveguide width (W) at 20 nm, inner circle radius (R1) at 154 nm, and widths of the outer and inner semi-circular cavity sections (W1 and W2) at 26 nm and 29 nm respectively, the sensor achieves a maximum sensitivity of 11573 nm/RIU within the refractive index range of 1 to 1.05, making it particularly suitable for gas sensing applications. Moreover, satisfactory performance is observed across other refractive index ranges relevant to various biosensing regions, including 1.2 to 1.3, 1.3 to 1.4, and 1.4 to 1.5. Both structures capitalize on the linear relationship between the refractive index of the medium and the resonant wavelength, enabling the identification and characterization of unknown materials. By filling the concentric semi-circular cavities with different unknown solutions, a linear shift in the transmission peak is observed, providing valuable information about the refractive index of these solutions. In conclusion, the optimized designs of these refractive index sensors showcase exceptional performance and hold significant potential for gas sensing and biosensing applications. Their ability to accurately detect and analyze unknown substances positions them as promising candidates for a wide range of chemical and biological sensing applications