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Browsing by Subject "circular dichroism"

Now showing 1 - 5 of 5
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    Characterizing mVenus adsorption to photodegraded polyethylene using circular dichroism and fluorescence spectroscopy
    (2022-08) Amaris, Althea
    Due to their versatility and relative cost-effectiveness, plastics as a material have gained increasing popularity and are heavily utilized by almost every major industry in the modern day. Their exponential rate of production coupled with a lack of proper disposal methods, however, have resulted in the global environmental issue of plastic pollution. Upon entering the ecosystem, plastic surfaces can act as a foundation for the formation of microbial communities known as biofilms. An initial key step to biofilm growth is the attachment of bacterial surface proteins onto the polymer. In this study, we examine structural changes of a “hard” model protein in the presence of environmentally relevant plastics. Using the intrinsic probes of the mVenus protein, a model yellow fluorescent protein (YFP), we study its structural response to variably photo-aged polyethylene (PE) through circular dichroism (CD) and tryptophan (W)/YFP-fluorescence spectroscopy. Upon binding to aged PE, mVenus undergoes mild secondary structure rearrangement. Interestingly, a forbidden transition in W-fluorescence is observed, evolving from the interaction between the sole tryptophan in mVenus and the increasingly hydrophilic surface of PE as the polymer is progressively photo-oxidized. The beta barrel and beta sheet structure of mVenus retains the overall stability of the protein, whereas the local structure and turn regions accommodate the protein-polymer interactions based on polymer surface chemistry. We can therefore start to predict that proteins bind variably during the initial docking of cells as the secondary structure behaves distinctly based on the age of the film to which it attaches. The dependence of protein docking on the extent of PE-irradiation reveals that film age, polymer type, and structural stability can either accelerate or inhibit biofilm growth.
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    Data for Chiral Optical Properties of Metasurfaces Comprised of Chiral Media: Effects of Geometric and Material Chirality
    (2024-07-15) Ramamurthy, Maya; Cote, Bryan M; Ferry, Vivian E; veferry@umn.edu; Ferry, Vivian E; Department of Chemical Engineering and Materials Science, University of Minnesota
    Chiral nanomaterials and metamaterials are the subject of intense recent interest, but the principles that govern their design can be challenging to identify. With the emergence of a host of new chiral molecules and nanocrystals, metamaterials can be created from materials that are intrinsically chiral, potentially enhancing chiroptical properties by combining geometrical and material factors. To take advantage of this, we first need to deconvolute the distinct and sometimes competing effects of geometric and material chirality on chiroptical properties. Here, we investigate the role of the meta-atom geometry, optical resonances, and chirality of the constituent medium on the optical chirality enhancement, circular dichroism (CD), g-factor, and relative transmission of LCP versus RCP light (∆T) in metasurfaces comprised of chiral material. We find that overlapping Mie-like resonances in nanodisk arrays lead to 6-fold CD enhancement compared to a uniform film. Our analysis also suggests that making the medium chiral does not necessarily increase CD or g-factor; enhancement in the CD and optical chirality depend on the magnitude of the Pasteur parameter as well as its real and imaginary components. As a demonstration of how geometric and material chirality can be combined to enhance chiroptical properties, we design a geometrically chiral meta-atom out of chiral media and observe over 9-fold enhancement in both CD and g-factor compared to a metasurface comprised of achiral material. This work systematically investigates different approaches to tailoring a chiral response from nanostructured arrays and provides design rules that can be broadly applied to metastructures comprised of chiral media.
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    Supporting Data for Circular Dichroism of Distorted Double Gyroid Thin Film Metamaterials
    (2024-11-04) McGuinness, Emily; Magruder, Benjamin; Dorfman, Kevin; Ellison, Chris; Ferry, Vivian; veferry@umn.edu; Ferry, Vivian; Department of Chemical Engineering and Materials Science, University of Minnesota
    Strong circular dichroism (CD) has been reported in triply periodic, co-continuous gyroid thin films for certain orientations and surface terminations. However, processing of gyroid thin films introduces distortions experimentally, creating a mismatch between the structures created practically and those explored computationally. This work explores the impact of compression normal to the substrate (z-compression) with conserved volume in (110)-oriented plasmonic silver double gyroid thin films on CD using finite-difference time-domain (FDTD) simulations. As compression reaches fifteen percent and above, new features emerge including termination-dependent opposite-handed CD responses and, at larger compressions, shorter wavelength responses that span many surface terminations. The longest wavelength responses of the system red-shift with increasing compression. The top surface structure contributes strongly to the emerging opposite-handed features and red-shifting of wavelengths. However, the less surface termination dependent features arise from a mixture of contributions from the top surface and interior of the films. Interplay of these leads to CD-switching phenomena as a function of compression for certain terminations and wavelengths. When alternative methods are utilized to compress the system, such as compression with a Poisson’s ratio of 0.33 (comparable to polystyrene) or the generation of compressed equilibrium structures with non-affine strut changes via self-consistent field theory, similar optical responses persist. Overall, this study highlights the significant impact experimentally relevant distortions (especially compression and some non-affine structural shifts) can have on the CD response of block copolymer templated plasmonic double gyroid thin films, and provides mechanistic insight into the film interior versus surface contributions to the CD response during compression.
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    Supporting data for Surface Structure Dependent Circular Dichroism in Single and Double Gyroid Metamaterials
    (2022-06-16) William, Lenart R; Ellison, Christopher J; Ferry, Vivian E; Cote, Bryan M; veferry@umn.edu; Ferry, Vivian E.; Materials Research Science & Engineering Center
    Data includes the processed FDTD simulation results needed to recreate the figures in "Surface Structure Dependent Circular Dichroism in Single and Double Gyroid Metamaterials". The data files include single and double gyroids' reflection, transmission, and absorption spectra, near-field electric field intensity enhancements, and the gyroid 3D models used in the FDTD simulations.
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    Tuning the Chiral Optical Response of Metamaterial and Metamaterial-Semiconductor Nanocrystal Hybrid Systems
    (2020-06) Pachidis, Pavlos
    Chiral metamaterials have been proposed as a promising platform for exotic optoelectronic applications such as ultrasensitive sensors, 3D displays, and ultrafast optical circuits. The functionality of such devices depends on their ability to dynamically change their optical response when a stimulus is applied. However, there are few examples and strategies for designing chiral systems with dynamically tunable optical response without necessitating reconfiguration of the chiral assembly. This thesis presents nanostructures with chiroptical response that can be tuned by modifying the refractive index of non-metallic components, and examines the effect of different design parameters on both circular dichroism and circularly polarized photoluminescence (PL). We show a chiral metamaterial system with metallic and dielectric components, where the refractive index of the dielectric component tunes the dissymmetry in transmission of right and left circularly polarized light (RCP, LCP). We then study the polarization of PL from chiral gold nanorod dimer arrays coated with poly(lauryl methacrylate) - CdSe/CdS quantum dot (QD) composite films. For these studies, we constructed a Fourier space polarimeter and demonstrated how changing the pitch of the periodic array, altering the luminescent material, introducing a dielectric spacer layer, and modulating the refractive index of the underlying substrate affects the handedness and directionality of the PL of the QD film. Finally, we show using finite-difference time-domain simulations that the placement of luminescent nanostructures within the unit cell of metallic arrays leads to enhanced degrees of circularly polarized PL compared to luminescent films that coat the metallic arrays uniformly. In this fashion, metamaterials with highly tailored directionality and polarization of PL can be designed and built. We fabricate assemblies of gold nanorods with QD nanopillars as well as assemblies of nanostructured QD solids via direct-write electron beam lithography, and show that these assemblies exhibit substantial chiroptical response. The results of this thesis encourage the integration of dielectric, phase change, or other materials with switchable optical properties in the design of chiral optical metamaterials, and expand the range of architectures and strategies for dynamically tunable chiroptical properties.