Enhanced Rainbow Trapping in Width-graded Chirped MIM Nano-gratings for High-sensitivity Multiwavelength Bio-molecular Detection

In this dissertation, we undertake theoretical and experimental investigations of plasmonic width-graded nano-gratings vis-à-vis a nanophotonic sensing platform amenable for integration within a Lab-on-a-Chip Point-of-Care system. Theoretically, we delineate the four principal surface plasmon polariton coupling and its interaction mechanisms in subwavelength gratings, thus showing their significant role in shaping the optical response of a plasmonic grating. Within the framework of width-graded metal-insulator-metal (MIM) nano-gratings, mode confinement and waveguiding result in multiwavelength light localization provided conditions for adiabatic mode transformation are satisfied. Maximal field enhancement is attained by ensuring adiabatic mode transformation among the grooves through parametric optimization of groove width and groove-to-groove separation. Experimentally, we fabricate nano-gratings using electron beam lithography with a minimum groove width of 40 nm at the center of the grating. Upon illumination, maximal enhanced electromagnetic field is generated at the center because of plasmonic light trapping and waveguiding; this is observed through near-field scanning optical microscopy, Raman spectroscopy, fluorescence spectroscopy, and corroborated via numerical simulations. Further, we compare near-field optical response of two types of plasmonic width-graded nano-gratings: Silicon-Metal-Insulator-Metal-Silicon (SMIMS) nano-gratings and MIM nano-gratings in rectangular and bull’s eye geometries. Through integration of the SMIMS width-graded nano-grating within a microfluidic device, we demonstrate that SERS enhancement factors of 106–107 are possible for detection of 1mM aqueous phospholipid solution at 532 nm, 638 nm, and 785 nm laser illumination. The highly intense multiwavelength characteristic of these nano-grating facilitates access to weak Raman modes. We employ MIM width-graded nano-gratings as a SERS platform for the detection of propylene glycol. We show detection down to the attomolar concentration level for this small molecule at three wavelengths of 532 nm, 638 nm, and 785 nm. The robust multiwavelength SERS measurements enable us to obtain quantitative analysis for various vibrational modes at concentration levels spanning 15 orders of magnitude from millimole to attomole per litre. These sub-wavelength width-graded nano-gratings offer rainbow trapping and highly robust plasmonic field enhancement which can be tuned to cover broad wavelength ranges within the visible and near-infrared regimes. These nano-gratings provide a viable platform for static and dynamic characterization of low concentration species.

Department dc:contributor.department

Electrical and Computer Engineering

Year dc:date.issued

2020

Author dc:creator

• Shayegannia, Moein

Advisor dc:contributor.advisor

• Kherani, Nazir P

• Nanograting
• Plasmonics
• Rainbow Trapping
• Single Molecule Sensing
• Surface Enhanced Raman Scattering
• Surface Plasmon Polariton

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Handle dc:identifier.uri

http://hdl.handle.net/1807/121524

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/121524