Design of plasmonic nanohole arrays on planar substrate and phtotnic crystal fibre tip for sensing application / Md Junayed

Md , Junayed (2023) Design of plasmonic nanohole arrays on planar substrate and phtotnic crystal fibre tip for sensing application / Md Junayed. Masters thesis, Universiti Malaya.

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Abstract

Plasmonic sensing technology has attracted a lot of attention in ultrasensitive label-free bio and chemical sensing in recent years. A unique plasmonic nanohole structure with excellent transmission efficiency and nanometer-level linewidth is required to enable sensitive and specific biosensing. The research on sharp peaks mechanism in the transmission spectra for sensitivity detection as well as portability has been barely touched. Additionally, integrating plasmonic nanohole arrays on optical fiber tips is preferred over planar substrate due to its lightweight feature, immunity to electromagnetic interference, robustness, and miniaturization. Due to computational limitations, previous studies examined only a single unit cell of the plasmonic structure in periodic settings prior to fabrication. To the best of my knowledge, this is the first time where the complete plasmonic nanohole arrays on optical fiber tip has been numerically computed for investigating the optical properties. In this thesis, plasmonic nanohole arrays on both planar substrate and photonic crystal fiber tip were studied which is enriched with multiple asymmetric spectral resonances. Numerous excitations, such as localized and propagating surface plasmon resonances are enriched in proposed plasmonic nanohole arrays. The proposed nanohole array structure, electromagnetic field distribution, and sensitivity were quantitatively analyzed using the fully vectorial finite-difference time-domain (FDTD) method. Commercially available FDTD and MODE solver Lumerical Software has been utilized to implement this numerical study. The confinement of electric near-field distribution revealed the nature of propagating and localized surface plasmon resonances whereas the magnetic field distribution also revealed the different plasmonic modes within the nanohole. The proposed unit cell of octamer nanohole arrays on planar substrate has a figure of merit of 148.29, and an extremely high bulk sensitivity of 436.8 nm/RIU for the analyte layer refractive index of 1.33 to 1.38. The proposed octamer nanohole array sensor also showed a surface sensitivity of 9.876 nm/nm for the detection of an immobilized DNA monolayer. The proposed octamer nanohole array has a nanometer-level spectral linewidth of 1.81 nm and more than 70% transmission at wavelengths between 600 and 1150 nm. The proposed complete octamer nanohole arrays on optical fiber tip has a bulk sensitivity of 351.08 nm/RIU for the analyte layer refractive index of 1.33 to 1.38. Thus, proposed nanohole arrays can be used in both biosensing and chemical detection.

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