Quantifying Electrophoretic Deposition of Nanocrystal Superlattices Using Quartz Crystal Microbalance

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Controlled electrochemical growth of ultra-long gold nanoribbons

Citation: Basnet, G., Panta, K. R., Thapa, P. S., & Flanders, B. N. (2017). Controlled electrochemical growth of ultra-long gold nanoribbons. Applied Physics Letters, 110(7), 5. doi:10.1063/1.4976027This paper describes the electrochemical growth of branchless gold nanoribbons with similar to 40 nm x similar to 300 nm cross sections and >100 mu m lengths (giving length-to-thickness aspect ratios of > 10(3)). These structures are useful for opto-electronic studies and as nanoscale electrodes. The 0.75-1.0V voltage amplitude range is optimal for branchless ribbon growth. Reduced amplitudes induce no growth, possibly due to reversible redox chemistry of gold at reduced amplitudes, whereas elevated amplitudes, or excess electrical noise, induce significant side-branching. The inter-relatedness of voltage-amplitude, noise, and side-branching in electrochemical nanoribbon growth is demonstrated. Published by AIP Publishing

Laser-Induced Electron Emission from Au Nanowires: A Probe for Orthogonal Polarizations

Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, provides spatially coherent and temporally short electron pulses. The properties of the photoelectron yield give insight into both the material properties of the nanostructure and the exciting laser focus. Ultralong nanoribbons, grown as a single crystal attached to a metallic taper, are sources of electron field emission that have not yet been characterized. In this report, photoemission from gold nanoribbon samples is studied and compared to emission from tungsten and gold tips. We observe that the emission from sharp tips generally depends on one transverse component of the exciting laser field, while the emission of a blunted nanoribbon is found to be sensitive to both components. We propose that this property makes photoemission from nanoribbons a candidate for position-sensitive detection of the longitudinal field component in a tightly focused beam

Forces at Individual Pseudopod-Filament Adhesive Contacts

On-chip cellular force sensors are fabricated from cantilever poly(3,4-ethylene dioxythiophene) filaments that visibly deflect under forces exerted at individual pseudopod-filament adhesive contacts. The shape of the deflected filaments and their ∼3 nN/μm spring constants are predicted by cantilever rod theory. Pulling forces exerted by Dictyostelium discoideumcells at these contacts are observed to reach ∼20 nN without breaking the contact

Directional growth of polypyrrole and polythiophene wires

This work establishes an innovative electrochemical approach to the template-free growth of conducting polypyrrole and polythiophene wires along predictable interelectrode paths up to 30 um in length. These wires have knobby structures with diameters as small as 98 nm. The conductivity of the polypyrrole wires is 0.5+/=0.3 S cm-1; that of the polythiophene wires is 7.6+/=0.8 S cm-1. Controlling the growth path enables fabrication of electrode-wire-target assemblies where the target is a biological cell in the interelectrode gap. Such assemblies are of potential use in cell stimulation studies.Peer reviewedPhysicsMicrobiology and Molecular Genetic

One-step synthesis of graphene via catalyst-free gas-phase hydrocarbon detonation

A one-step, gas-phase, catalyst-free detonation of hydrocarbon (C[subscript 2]H[subscript 2]) method was developed to produce gram quantities of pristine graphene nanosheets (GNs). The detonation of C[subscript 2]H[subscript 2] was carried out in the presence of O[subscript 2]. The molar ratios of O[subscript 2]/C[subscript 2]H[subscript 2] were 0.4, 0.5, 0.6, 0.7, and 0.8. The obtained GNs were analyzed by XRD, TEM, XPS and Raman spectroscopy. The GNs are crystalline with (002) peak centered at 26.05° (d = 0.341 nm). TEM shows that the GNs are stacked in two to three layers and sometimes single layers. An increase in the size of GNs (35-250 nm) along with reduction in defects (Raman I[subscript D]/I[subscript G]~ 1.33- 0.28) and specific surface area (187 to 23 m²gˉ¹) was found with increasing O[subscript 2] content. The high temperature of the detonation, ca. 4000K, is proposed as the cause of graphene production rather than normal soot. The method allows for the control of the number of layers, shape and size of the graphene nanosheets. The process can be scaled up for industrial production

Laser-Induced Electron Emission from Au Nanowires: A Probe for Orthogonal Polarizations

Photoelectron field emission, induced by femtosecond laser pulses focused on metallic nanotips, provides spatially coherent and temporally short electron pulses. The properties of the photoelectron yield give insight into both the material properties of the nanostructure and the exciting laser focus. Ultralong nanoribbons, grown as a single crystal attached to a metallic taper, are sources of electron field emission that have not yet been characterized. In this report, photoemission from gold nanoribbon samples is studied and compared to emission from tungsten and gold tips. We observe that the emission from sharp tips generally depends on one transverse component of the exciting laser field, while the emission of a blunted nanoribbon is found to be sensitive to both components. We propose that this property makes photoemission from nanoribbons a candidate for position-sensitive detection of the longitudinal field component in a tightly focused beam

Ethanol Shock and Lysozyme Aggregation

Irreversible protein–protein aggregation is associated with several human maladies, including Alzheimer\u27s disease, and poses a challenge to pharmaceutical formulation and preservation efforts. The existence of multiple agglomeration pathways that lead to different final morphologies complicates the ability to determine the aggregation fate of proteins under various reaction conditions. Using lysozyme (3 mg mL−1) as a model protein for dynamic light scattering and circular dichroism studies, we observed dense, non-fibrous aggregation triggered under acidic (pH 4) conditions by a destabilizing “ethanol shock” of 16% (v/v) ethanol. However,ethanol concentrations 15% and below did not lead to aggregation. The aggregation fate of these proteins is thus found to be extremely sensitive to the denaturant concentration. We introduce a stochastic model to explain this dependence based on the denaturant-induced population of a partially unfolded state

Long reach cantilevers for sub-cellular force measurements

Maneuverable, high aspect ratio poly 3-4 ethylene dioxythiophene (PEDOT) fibers are fabricated for use as cellular force probes that can interface with individual pseudopod adhesive contact sites without forming unintentional secondary contacts to the cell. The straight fibers have lengths between 5 and 40 μm and spring constants in the 0.07–23.2 nN μmˉ¹ range. The spring constants of these fibers were measured directly using an atomic force microscope (AFM). These AFM measurements corroborate determinations based on the transverse vibrational resonance frequencies of the fibers, which is a more convenient method. These fibers are employed to characterize the time dependent forces exerted at adhesive contacts between apical pseudopods of highly migratory D. discoideum cells and the PEDOT fibers, finding an average terminal force of 3.1± 2.7 nN and lifetime of 23.4 ± 18.5 s to be associated with these contacts