Plasmon-exciton coupling for signal amplification and biosensing : fundamentals and application
- UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
- Frank James Tukur (Creator)
- Institution
- The University of North Carolina at Greensboro (UNCG )
- Web Site: http://library.uncg.edu/
- Advisor
- Wei Jianjun
Abstract: Surface plasmon resonance (SPR) is the collective oscillation of frequency-matched free-space photons and surface electrons at a metal/dielectric interface. Their inherent sensitivity to refractive index changes and ability to couple with exciton species and enhance light-matter interaction make them ideal candidates for low-concentration analyte detection compared to conventional biosensors. The use of metal nanostructures and nanomaterials to excite SPR represents the current state-of-the-art. However, the challenges associated with repeatable synthesis of uniform nanomaterials, complex nanostructure fabrication, low SPR generation efficiency and limited understanding of the mechanism of plasmon-exciton coupling for signal amplification have motivated the search for alternative architectures and procedures. The uniform and repeatable gold nanoslit (NS) and nanoledge (NL) array architectures offers a promising route towards addressing the above issues, and hence this research attempts to take advantage of these platforms to achieve efficient SPR generation and exciton coupling for biosensing applications. The overarching scope of this dissertation extends to the design, fabrication, and optimization of metal NS and NL structures for SPR generation and sensing applications. Emphasis is placed on investigating the mechanism of optical signal enhancement arising from plasmon-exciton coupling (PEC) with particular focus on (a) exploring the role of geometry and size of the nanostructures (b) examining the influence of SPR spectral mode overlap with exciton’s absorption and/or emission energies on the overall optical signal in a NS or NL system, and (c) investigating the analytical sensitivity and signal transduction of the PEC system to biomolecular interactions. The nanoimprinting technique based on soft lithography for NS fabrication, which is used in this work for NS array fabrication, required addressing a critical issue, namely PDMS diffusion into nanoscale patterns for high aspect ratio realization. This was mitigated by curing temperature variation and incubation time to achieve 50 nm-130 nm width NS arrays with an intense, broad spectral response that red-shifts and diminishes with increasing NS width. The 50 nm width structure exhibited ~57× optical enhancement when coupled with acridine orange, a fluorescence dye, whose absorption and emission spectra closely overlaps with plasmonic spectra. A sensitive assay for detecting DNA hybridization was generated using the interaction of the selected SARS-CoV-2 ssDNA and dsDNA with AO to trigger the metachromatic behaviour of the dye to produce a strong optical signal amplification on the formation of AO-ssDNA complex and a quenched signal upon hybridization to the complementary target DNA along with a blue shift in the fluorescence of AO-dsDNA. The SARS-CoV-2 DNA hybridization assay, based on the PEC exhibited 0.21 nM sensitivity to complementary strand target, distinguished 1-, 2-, and 3-base mismatched DNA targets, reusability of ~6 x with 96% signal recovery, stable for up to 10 days at room temperature. Regarding the NL sensing platform, the principle of the sensing mechanism is based on plasmon-mediated extraordinary optical transmission (EOT) whose wavelength red-shifts with increase in refractive index (RI) at near-metal surface. The NL plasmonic-based biosensor fabricated using a patented E-beam writing method exhibited ~ 384.08 nm/RIU sensitivity, limit of detection to cardiac troponin I (TnI) at 0.079 ng/mL, 0.084 ng/mL and 0.097 ng/mL in PBS buffer, human serum, and human blood, respectively. The direct measurement of TnI in whole human blood without any purification or sample preparation step highlights the significance of the sensing platform for point-of-care detection. Thus, this work innovates (a) a tunable SPR to meet the requirement for plasmon-exciton spectral overlap for optical signal amplification, (b) the mechanism of optical enhancements due to PEC in NS arrays, and (c) a new application of PEC in NS and EOT in NL for the sensitive detection of SARS-CoV-2 DNA hybridization and cardiovascular biomarker TnI in human blood, respectively. The enhanced light-matter interactions have a broader impact beyond healthcare to light harvesting for solar cells, heat generation for cancer therapy, and photocatalysis for nanoscale reactions like water splitting.
Plasmon-exciton coupling for signal amplification and biosensing : fundamentals and application
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Created on 5/1/2023
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Additional Information
- Publication
- Dissertation
- Language: English
- Date: 2023
- Keywords
- DNA sensing, Nanoledge array, Nanoslit array, Plasmon-exciton coupling, Signal amplification, Troponin I
- Subjects
- Surface plasmon resonance
- Nanostructured materials
- Exciton theory
- Biosensors