Abstract:: Plasmonic nanostructures have been extensively studied for their potential application in numerous fields such as nanophotonics, biosensors, and bioimaging. One of the key properties of nanostructures that can be manipulated for practical applications is their capabilities to modulate the optical and photophysical properties of fluorophores residing nearby. Surface plasmons (SP), which can be defined as the collective oscillation of the delocalized electrons, are the fundamental characteristic of nanostructures that are primarily responsible for altering those properties. Elucidating fluorophores at the single-molecule level has received significant attention since more specific information can be extracted from single molecule-based studies, which otherwise, could be obscured in ensemble studies. However, single-molecule studies are inherently challenging because the signal from a single molecule is usually deem, which makes it difficult to detect. The situation is even worse in the case of a crowded environment due to higher background noise, such as cellular autofluorescences in the case of cell-based studies. Thus, one of the possible ways out of this single-molecule detection problem is to couple the fluorophore with a plasmonic nanostructure which can potentially enhance the fluorescence intensity of the single fluorophore leading to the improvement in signal to noise ratio. Throughout the projects presented here, I studied the fluorescence characteristics of single fluorophore molecules coupled in a plasmonic nano-aperture which is termed as Zero Mode Waveguides (ZMWs). I utilized single fluorophores of different origins, such as organic dyes and quantum dots (QDs), in ZMWs of different metallic compositions. By probing ZMWs made from the mixture of Aluminum and gold, with a range of ATTO dyes emitting across the visible wavelength, we found that the surface plasmon resonance of ZMWs is tunable by optimizing the metal ratio. Apart from the ATTO dyes, I investigated the photoluminescence (PL) behavior of single QDs in ZMWs and observed a significant enhancement in PL intensity and a substantial improvement in the blinking characteristics of the QDs, which are beneficial for the utility of QDs as a bio-imaging agent or a single-photon source. Single QDs in ZMWs exhibited a significant enhancement in biexciton quantum yield, which is crucial for their potential application in lasing where materials with a high optical gain are desired. I also examined the fluorescence properties of the single fluorophores in gold ZMWs in the presence of a gold nanoparticle (AuNP) and observed a more significant enhancement in fluorescence intensity in the gap between AuZMW and AuNP compared to the case of only AuZMW or only AuNP. The experimental design and the resulting findings throughout the three projects presented here should be a valuable resource for the future development of plasmon-mediated single-molecule studies.

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https://uky.zoom.us/j/88903093777

Abstract: Biological polymer networks such as mucus, extracellular matrix, nuclear pore complex, and bacterial biofilms, play a critical role in governing the transport of nutrients, biomolecules and particles within cells and tissues. The interactions between particle and polymer chains are responsible for effective selective filtering of particles within these macromolecular networks. This selective filtering is not dictated by steric alone but must use additional interactions such electrostatics, hydrophobic and hydrodynamic effects to control particle transport within biogels. Depending on chemical composition and desired function, biogels use selective filtering to allow some particles to permeate while preventing others from penetrating the biogel. The mechanisms underlying selective filtering are still not well understood yet have important ramifications for a variety of biomedical applications. Controlling these non-steric interactions are critical to understanding molecular transport in vivo as well as for engineering optimized gel-penetrating therapeutics. Fluorescence correlation spectroscopy (FCS) is an ideal tool to study particle transport properties within uncharged and charged polymer solutions. In this dissertation, our research focuses primarily on the role of electrostatics on the particle diffusion behavior within polymer solutions in the semi-dilute and concentrated regimes.

Using a series of charged dye molecules, with similar size and core chemistry but varying net molecular charge, we systematically investigated their diffusion behavior in polymer solutions and networks made up of polysaccharide and proteins. Specifically, we studied in Chapter 3 the probe diffusion in semidilute and concentrated dextran solutions. The hindered diffusion observed in attractive gels is dependent on the probe net charge and shows a dependence on the solution ionic strength. Using a biotinylated probe, we also show evidence of an additional non-electrostatic interaction between the biotin molecule and the dextran polymer chains. In contrast, comparisons to a highly charged, water soluble polyvinylamine (PVAm) semidilute solution shows that all probes, regardless of charge, were highly hindered and a weaker dependence on solution ionic strength was observed. In Chapter 4, we characterized the transport properties of our probe molecules within pure and mixed charge solutions of amino(+)-dextran and carboxymethyl(-)-dextran. We show that these mixed charge polymer solutions still have the potential to be efficient filters for interacting particles even with comparably few attractive interaction sites. By chemical modification of the amino dextran, we also compare these results to those obtained in polyampholytic solutions. Lastly, we investigate the transport properties of both probes and a much larger bovine serum albumin (BSA) protein molecule within liquid-liquid phase separated (LLPS) tau protein in chapter 5. Tau is an intrinsically disordered protein with both positive and negatively charged amino acids. We show that despite having a high local protein concentration, tau droplets are relatively low density and comparable to semi-dilute polymer solutions. Both probe molecules and BSA are observed by FCS to be recruited within the liquid droplet resulting in ~10x fold increase in particle concentration inside the tau droplet compared to outside. Probe transport within the phase separated tau is sensitive to probe net charge and solution ionic strength. Lastly, we show that BSA transport inside the tau droplet can be fairly well described by using Stokes-Einstein adjusted for the experimentally determined microviscosity within the tau droplet.

Keywords: diffusion, biological gels, fluorescence correlation spectroscopy, electrostatic, interaction filtering.

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The Department of Chemistry hosts a Graduation Celebration and Awards Ceremony to recognize the outstanding acheivements of our students on an annual basis. This year's event will be streamed via Facebook. Please join us by clicking here!

We are delighted to recognize the following graduates of our PhD, Masters, and Undergraduate programs:

Abstract: Process analytical technology (PAT) plays an essential role in understanding and optimization chemical manufacturing routes by furnishing data-dense reaction profiles. However, each PAT tool presents certain limitations with respect to chemical component resolution, reaction compatibility or useful operational domain. High-pressure liquid chromatography (HPLC) represents one of the most versatile analytical tools available for providing detailed reaction progress analysis. Yet this technology introduces a new set of challenges relating to sample acquisition and preparation, especially when trying to utilize HPLC as a real time analytical technology.

Our lab has developed a comprehensive set of automated tools, which allow nearly any chemical process to be visualized in real time by HPLC. This includes reactions performed under inert atmosphere, systems with heterogenous reagents, and complex competition reactions with many components. The combination of excellent resolving power of UHPLC, coupled to the high dynamic range of standard UV/Vis and MSD detectors has allowed this tool to be broadly deployed. This has allowed complex reactions to be visualized in exceptional details with unprecedented ease. This presentation will discuss several case studies to demonstrate the flexibility and fidelity of this new online HPLC technology. Examples will include studying reaction mechanisms, measuring crystallization processes and deployment as an in-process control for reaction automation.

Abstract:

Imparting supramolecular interactions on transition metal systems such as Iridium complexes (with various N^C ligands), can have a profound impact on their luminescence properties. These types of complexes are under intensive investigation due to their excellent performance when used as emitters in phosphorescent organic light emitting diodes (PhOLEDs).¹ The ideal interactions for holding supramolecular systems together are hydrogen bonds, as they combine relatively strong intermolecular attractions with excellent reversibility. In using DNA base-pair-like interactions in super strong hydrogen bonding arrays to drive assembly,² we can influence chromaticity efficiently.^3,4 Beyond molecular systems, we can also apply these principles in extended solid-state systems whose porosities are such that small molecule uptake can influence the inherent physical (and photophysical) properties of the host materials.⁵ In this lecture, a broad view of our research program will be presented, spanning molecular systems to solid-state materials, and how we can make use of inherent luminescence properties for chromaticity modulation, small molecule sensing, and diagnostics.^6,7

References:

1. A.F. Henwood, E. Zysman-Colman, Chem. Commun. 2017, 53, 807.
2. B.A. Blight, C.A. Hunter, D.A. Leigh, H. McNab, P.I.T. Thomson, Nature Chemistry, 2011, 3, 246.
3. B. Balónová, D.  Rota Martir, E.R. Clark, H.J. Shepherd, E. Zysman-Colman, B.A. Blight, Inorganic Chemistry, 2018, 57, 8581.
4. B. Balónová, H.J.  Shepherd, C.J. Serpell, B.A. Blight, Supramolecular Chemistry, 2019, DOI: 10.1080/10610278.2019.1649674
5. R.J. Marshall, Y. Kalinovskyy; S.L. Griffin, C. Wilson, B.A. Blight, R.S. Forgan, J. Am. Chem. Soc., 2017, 139, 6253.
6. S.J. Thomas, B. Balónová, J. Cinatl M.N. Wass, C.J. Serpell, B.A. Blight, M. Michaelis, ChemMedChem, 2020, 15(4), 349.
7. C.S. Jennings, J.S. Rossman, B.A. Hourihan, R.J. Marshall, R.S. Forgan, B.A. Blight, Soft Matter, 2021, In Press. DOI: 10.1039/D0SM02188A