4 research outputs found

    Molecular Precision at Micrometer Length Scales: Hierarchical Assembly of DNA–Protein Nanostructures

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    Robust self-assembly across length scales is a ubiquitous feature of biological systems but remains challenging for synthetic structures. Taking a cue from biologywhere disparate molecules work together to produce large, functional assemblieswe demonstrate how to engineer microscale structures with nanoscale features: Our self-assembly approach begins by using DNA polymerase to controllably create double-stranded DNA (dsDNA) sections on a single-stranded template. The single-stranded DNA (ssDNA) sections are then folded into a mechanically flexible skeleton by the origami method. This process simultaneously shapes the structure at the nanoscale and directs the large-scale geometry. The DNA skeleton guides the assembly of <i>RecA</i> protein filaments, which provides rigidity at the micrometer scale. We use our modular design strategy to assemble tetrahedral, rectangular, and linear shapes of defined dimensions. This method enables the robust construction of complex assemblies, greatly extending the range of DNA-based self-assembly methods

    Fabrication of Scanning Electrochemical Microscopy-Atomic Force Microscopy Probes to Image Surface Topography and Reactivity at the Nanoscale

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    Concurrent mapping of chemical reactivity and morphology of heterogeneous electrocatalysts at the nanoscale allows identification of active areas (protrusions, flat film surface, or cracks) responsible for productive chemistry in these materials. Scanning electrochemical microscopy (SECM) can map surface characteristics, record catalyst activity, and identify chemical products at solid–liquid electrochemical interfaces. It lacks, however, the ability to distinguish topographic features where surface reactivity occurs. Here, we report the design and fabrication of scanning probe tips that combine SECM with atomic force microscopy (AFM) to perform measurements at the nanoscale. Our probes are fabricated by integrating nanoelectrodes with quartz tuning forks (QTFs). Using a calibration standard fabricated in our lab to test our probes, we obtain simultaneous topographic and electrochemical reactivity maps with a lateral resolution of 150 nm

    Local Structure and Global Patterning of Cu<sup>2+</sup> Binding in Fibrillar Amyloid‑β [Aβ(1–40)] Protein

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    The amyloid-β (Aβ) protein forms fibrils and higher-order plaque aggegrates in Alzheimer’s disease (AD) brain. The copper ion, Cu<sup>2+</sup>, is found at high concentrations in plaques, but its role in AD etiology is unclear. We use high-resolution pulsed electron paramagnetic resonance spectroscopy to characterize the coordination structure of Cu<sup>2+</sup> in the fibrillar form of full-length Aβ(1–40). The results reveal a bis-<i>cis</i>-histidine (His) equatorial Cu<sup>2+</sup> coordination geometry and participation of all three N-terminal His residues in Cu<sup>2+</sup> binding. A model is proposed in which Cu<sup>2+</sup>-His6/His13 and Cu<sup>2+</sup>-His6/His14 sites alternate along the fibril axis on opposite sides of the β-sheet fibril structure. The local intra-β-strand coordination structure is not conducive to Cu<sup>2+</sup>/Cu<sup>+</sup> redox-linked coordination changes, and the global arrangement of Cu sites precludes facile multielectron and bridged-metal site reactivity. This indicates that the fibrillar form of Aβ suppresses Cu redox cycling and reactive oxygen species production. The configuration suggests application of Cu<sup>2+</sup>-Aβ fibrils as an amyloid architecture for switchable electron charge/spin coupling and redox reactivity

    Effect of Tin Doping on α-Fe<sub>2</sub>O<sub>3</sub> Photoanodes for Water Splitting

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    Sputter-deposited films of α-Fe<sub>2</sub>O<sub>3</sub> of thickness 600 nm were investigated as photoanodes for solar water splitting and found to have photocurrents as high as 0.8 mA/cm<sup>2</sup> at 1.23 V vs the reversible hydrogen electrode (RHE). Sputter-deposited films, relative to nanostructured samples produced by hydrothermal synthesis,, permit facile characterization of the role and placement of dopants. The Sn dopant concentration in the α-Fe<sub>2</sub>O<sub>3</sub> varies as a function of distance from the fluorine-doped tin oxide (FTO) interface and was quantified using secondary ion mass spectrometry (SIMS) to give a mole fraction of cations of approximately 0.02% at the electrolyte interface. Additional techniques for determining dopant density, including energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), electrochemical impedance spectroscopy (EIS), and conductivity measurements, are compared and discussed. Based on this multifaceted data set, we conclude that not all dopants present in the α-Fe<sub>2</sub>O<sub>3</sub> are active. Dopant activation, rather than just increasing surface area or dopant concentration, is critical for improving metal oxide performance in water splitting. A more complete understanding of dopant activation will lead to further improvements in the design and response of nanostructured photoanodes
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