Semester

Spring

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Jeremy Dawson

Committee Member

David Graham

Committee Member

Charter Stinespring

Committee Member

Yuxin Liu

Committee Member

Dimitris Korakakis

Abstract

The biomedical industry has seen sustained growth over the past half century, with a continually increasing demand for flexible, easy-to-use, and cost-effective tools. One large area of commercial interest has been point-of-use or point-of-care diagnostics, using optical based Lab-On-Chip (LOC) style systems. Label and label-free fluorescence detection systems are common benchtop modalities that have seen recent integration into these portable, cost-effective LOC applications. However, despite their maturity, there are still opportunities to improve device characteristics, specifically in reference to throughput, limit-of-detection (LOD), and hybrid integration (along with associated costs).

Optical research avenues at WVU have focused on improving these systems with the addition of production scalable, engineered nano-structures that can be integrated into LOC systems, namely microfluidic channels or similar. A major goal of this dissertation’s research is to provide plasmonic based fabrication solutions that improve LOD, while also addressing throughput or cost concerns. The plasmonic effect utilizing localized surface plasmon resonance is commonly known from its use in surface enhanced Raman spectroscopy applications. Similarly, these resonant electric-field conditions can be engineered to desired wavelengths, where the resonant optical properties are reliant on the plasmonic material being used and the parametric attributes of the features. Another major goal of this research seeks to present a relationship between the simulated resonant E-Field intensities, and the resulting physical photonic output.

The work contained herein details the sim-to-fab-to-characterization development of visible wavelength optimized plasmonic lattice nano-structures for label-based fluorescence emission enhancement. Finite difference time-domain simulations were performed to obtain the ideal physical parameters for a wavelength of interest at 565nm with both a nanosphere base and optimized common geometry structure. Additionally, a full visible spectrum parametric analysis of common geometric features including cylinders, squares, triangles, and stars was performed, yielding resonant conditions at 614nm, 625nm, 648nm, 664nm, and 701nm. Two fabrication methods were developed to create the simulated structures. A novel methodology utilizing hydrogen silsesquioxane was able to achieve various high accuracy sub-100nm nanoscale features/lattices through electron beam lithography. A high throughput method of fabrication ideal for low-cost, large-scale operation using polystyrene nanospheres as a feature basis were also successfully explored. Characterization of the fabricated structures was explored by monitoring the effect of the plasmonic lattices on quantum dots when introduced to the patterned surfaces in a ‘flow-style’ application. Three different techniques including optical microscopy, confocal microscopy, and time-correlated single photon counting were utilized. At an initial concentration of 25nM an increase in intensity of ~2x to ~4x compared to background intensity was observed in initial efforts. The optimized structures, at a reduced concentration of 100-fold, down to .833nM were shown to have an increased photon output of ~1.6x-4x in comparison to a non-patterned gold surface. The reported results confirm a scalable relationship between simulated resonant E-field intensities and resulting photonic output from near field emitters.

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