Research on the high sensitivity plasmonic interferometer sensor with grid structure

Abstract

These days, the demand for biosensors is increasing due to population aging and changes in eating habits. Despite the high demand for biosensors, they are in an underdeveloped state. The reason for this is that the required features of biosensors are extremely different based on the measurement location and frequency. For providing these features, biosensors require the direct and accurate detection of target materials. Among the various biosensors, body fluids measurement is especially in demand. The potential application areas for this are diabetes and hormone-related problems. For these applications, the biosensor device should perform real-time measurement of the high sensitivities of the target materials. Pre-existing devices measure the levels of the target materials in the body fluids. Body fluids include blood, saliva, urine, interstitial fluids, and tears. In this thesis, research on the plasmonic interferometer sensor is included. The plasmonic interferometer operates based on the principles of surface plasmon resonance (SPR) and beam interference. The goal of this research is to suggest a unique grid structure and detect the refractive index change in the interface of the sensor. Previously, transmission-type SPR has been studied by many research groups. Transmission-type SPR sensors have advantages over the reflection types. One of the important features of the transmission type is the miniaturization of the sensing area while maintaining high sensitivity. In this research, a unique structure that features two-dimensional grooves and slits is suggested. The suggested structure is called a grid structure. Optimization of the structure is performed by FDTD simulation. The optimized structure is fabricated by focused ion beam (FIB) milling on Ag and Ti-deposited glass substrate. The fabricated grid structure is analyzed in terms of transmission (T), normalized transmission ($T_n$), relative intensity change (RIC), figure of merit (FOM), and sensitivity. The simulation and experiment are first done with a polarizer. After verifying the grid structure polarization independency, the experiment is performed without a polarizer. In the simulation, the grid structure shows peak intensity at 712nm in the air condition. At 648nm, the simulation value of the $FOM_I$ is 38.6 and the sensitivity is 272nm/RIU. In the experiment, the fabricated structure shows peak intensity at 642nm in the air condition. At 658nm, the experiment value of the $FOM_I$ is 36.85 and the sensitivity is 246nm/RIU.