Browsing by Author "Flatebo, Charlotte"

Now showing 1 - 6 of 6
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    Exploiting plasmons to sense interfacial changes at the nanoscale
    (2021-07-26) Flatebo, Charlotte; Landes, Christy F.
    Probing chemistry, especially at the nanoscale, provides insight into the mechanisms governing chemical reactions at interfaces and potential avenues for materials development. As a class of materials, plasmonic nanomaterials are a promising approach for probing chemistry at interfaces. When excited with an incident electric field like light, plasmonic nanomaterials exhibit localized surface plasmon resonances (LSPR). The LSPR scattering spectrum is sensitive to the size, shape and local environment of the nanoparticle. However, this sensitivity can be a limiting factor in applications of plasmonic materials in complex chemical environments. Contaminants in the environment can corrode or dissolve the nanomaterials, irreversibly changing the LSPR. The intrinsic heterogeneity of colloidally synthesized nanoparticles limits LSPR sensitivity to changes in the dielectric environment at the ensemble level. In my work, I use single-particle spectroelectrochemistry and correlated scanning electron microscopy to investigate the overall stability and utility of plasmonic nanomaterials in complex chemical environments. I demonstrate that we can utilize the plasmon to report on chemistry in complex environments and provide mechanistic insight into dissolution, polymer collapse, and future work in switchable electron density tuning in single plasmonic nanoparticles. Understanding the mechanisms governing these chemical processes at the nanoscale builds foundational science to support future technological developments in electronics, catalysis, and sensing.
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    Generalized recovery algorithm for 3D super-resolution microscopy using rotating point spread functions
    (Springer Nature, 2016) Shuang, Bo; Wang, Wenxiao; Shen, Hao; Tauzin, Lawrence J.; Flatebo, Charlotte; Chen, Jianbo; Moringo, Nicholas A.; Bishop, Logan D.C.; Kelly, Kevin F.; Landes, Christy F.
    Super-resolution microscopy with phase masks is a promising technique for 3D imaging and tracking. Due to the complexity of the resultant point spread functions, generalized recovery algorithms are still missing. We introduce a 3D super-resolution recovery algorithm that works for a variety of phase masks generating 3D point spread functions. A fast deconvolution process generates initial guesses, which are further refined by least squares fitting. Overfitting is suppressed using a machine learning determined threshold. Preliminary results on experimental data show that our algorithm can be used to super-localize 3D adsorption events within a porous polymer film and is useful for evaluating potential phase masks. Finally, we demonstrate that parallel computation on graphics processing units can reduce the processing time required for 3D recovery. Simulations reveal that, through desktop parallelization, the ultimate limit of real-time processing is possible. Our program is the first open source recovery program for generalized 3D recovery using rotating point spread functions.
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    Optically monitoring the electrochemical stability of single metallic nanocrystals in complex electrolyte environments
    (2018-05-03) Flatebo, Charlotte; Landes, Christy F
    Recent developments in life sciences technology, such as electrochemical biosensing, harness the unique properties of metallic nanocrystals. The localized surface plasmon resonance (LSPR) scattering spectra of gold nanocrystals are effective electrochemical sensors of both biological and organic molecules; however, the LSPR is directly related to the size and shape of the gold nanocrystals and the local environment. Changes in these parameters drastically affect gold nanocrystal functionality. Hyperspectral dark-field analysis and correlated scanning electron microscopy demonstrate that the ionic composition of complex electrolyte solutions containing predominantly chloride anions significantly influences the morphological stability of gold nanorods (AuNRs). The introduction of small concentrations of oxoanions with increasing numbers of hydroxyl groups drastically alters the dissolution onset potential and the dissolution pathway of single AuNRs. At high concentrations of chloride ions, both bicarbonate and phosphate ions prevent dissolution until applying highly anodic potentials. Applying an anodic bias to single anion chloride environments causes a drastic average red-shift. As the number of hydroxyl groups of the competing oxoanion increases, the magnitude of the shift decreases and then begins to blue-shift. Understanding the impact of complex anion solutions on the stability of metal nanocrystal modified electrodes improves capabilities of electrochemical biosensing by increasing the potential window for sensing of new species.
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    Single-Particle Hyperspectral Imaging Reveals Kinetics of Silver Ion Leaching from Alloy Nanoparticles
    (American Chemical Society, 2021) Al-Zubeidi, Alexander; Stein, Frederic; Flatebo, Charlotte; Rehbock, Christoph; Hosseini Jebeli, Seyyed Ali; Landes, Christy F.; Barcikowski, Stephan; Link, Stephan; Smalley-Curl Institute
    Gold–silver alloy nanoparticles are interesting for multiple applications, including heterogeneous catalysis, optical sensing, and antimicrobial properties. The inert element gold acts as a stabilizer for silver to prevent particle corrosion, or conversely, to control the release kinetics of antimicrobial silver ions for long-term efficiency at minimum cytotoxicity. However, little is known about the kinetics of silver ion leaching from bimetallic nanoparticles and how it is correlated with silver content, especially not on a single-particle level. To characterize the kinetics of silver ion release from gold–silver alloy nanoparticles, we employed a combination of electron microscopy and single-particle hyperspectral imaging with an acquisition speed fast enough to capture the irreversible silver ion leaching. Single-particle leaching profiles revealed a reduction in silver ion leaching rate due to the alloying with gold as well as two leaching stages, with a large heterogeneity in rate constants. We modeled the initial leaching stage as a shrinking-particle with a rate constant that exponentially depends on the silver content. The second, slower leaching stage is controlled by the electrochemical oxidation potential of the alloy being steadily increased by the change in relative gold content and diffusion of silver atoms through the lattice. Interestingly, individual nanoparticles with similar sizes and compositions exhibited completely different silver ion leaching yields. Most nanoparticles released silver completely, but 25% of them appeared to arrest leaching. Additionally, nanoparticles became slightly porous. Alloy nanoparticles, produced by scalable laser ablation in liquid, together with kinetic studies of silver ion leaching, provide an approach to design the durability or bioactivity of alloy nanoparticles.
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    Stargazin Modulation of AMPA Receptors
    (Elsevier, 2016) Shaikh, Sana A.; Dolino, Drew M.; Lee, Garam; Chatterjee, Sudeshna; MacLean, David M.; Flatebo, Charlotte; Landes, Christy F.; Jayaraman, Vasanthi; Applied Physics Graduate Program
    Fast excitatory synaptic signaling in the mammalian brain is mediated by AMPA-type ionotropic glutamate receptors. In neurons, AMPA receptors co-assemble with auxiliary proteins, such as stargazin, which can markedly alter receptor trafficking and gating. Here, we used luminescence resonance energy transfer measurements to map distances between the full-length, functional AMPA receptor and stargazin expressed in HEK293 cells and to determine the ensemble structural changes in the receptor due to stargazin. In addition, we used single-molecule fluorescence resonance energy transfer to study the structural and conformational distribution of the receptor and how this distribution is affected by stargazin. Our nanopositioning data place stargazin below the AMPA receptor ligand-binding domain, where it is well poised to act as a scaffold to facilitate the long-range conformational selection observations seen in single-molecule experiments. These data support a model of stargazin acting to stabilize or select conformational states that favor activation.
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    The structure–energy landscape of NMDA receptor gating
    (Springer Nature, 2017) Dolino, Drew M.; Chatterjee, Sudeshna; MacLean, David M.; Flatebo, Charlotte; Bishop, Logan D.C.; Shaikh, Sana A.; Landes, Christy F.; Jayaraman, Vasanthi
    N-Methyl-D-aspartate (NMDA) receptors are the main calcium-permeable excitatory receptors in the mammalian central nervous system. The NMDA receptor gating is complex, exhibiting multiple closed, open, and desensitized states; however, central questions regarding the conformations and energetics of the transmembrane domains as they relate to the gating states are still unanswered. Here, using single-molecule Förster resonance energy transfer (smFRET), we map the energy landscape of the first transmembrane segment of the Rattus norvegicus NMDA receptor under resting and various liganded conditions. These results show kinetically and structurally distinct changes associated with apo, agonist-bound, and inhibited receptors linked by a linear mechanism of gating at this site. Furthermore, the smFRET data suggest that allosteric inhibition by zinc occurs by an uncoupling of the agonist-induced changes at the extracellular domains from the gating motions leading to an apo-like state, while dizocilpine, a pore blocker, stabilizes multiple closely packed transmembrane states.