29 research outputs found
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 μm-1 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
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
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
Physical characterixation and in vitro biological impact of highly aggregated antibodies separated into size-enriched populations by fluorescence-activated cell sorting
An IgG2 monoclonal antibody (mAb) solution was subjected to stirring, generating high concentrations of nanometer and subvisible particles, which were then successfully size enriched into different size bins by low speed centrifugation or a combination of gravitational sedimentation and Fluorescence-Activated Cell Sorting (FACS). The size-fractionated mAb particles were assessed for their ability to elicit the release of cytokines from a population of donor-derived human peripheral blood mononuclear cells (PBMC) at two phases of the immune response. Fractions enriched in nanometer-sized particles showed a lower response than those enriched in micron-sized particles in this assay. Particles of 5–10 μm in size displayed elevated cytokine release profiles compared to other size ranges. Stir-stressed mAb particles had amorphous morphology, contained protein with partially altered secondary structure, elevated surface hydrophobicity (compared to controls), and trace levels of elemental fluorine. FACS size-enriched the mAb particle samples, yet did not notably alter the overall morphology or composition of particles as measured by Microflow imaging, Transmission Electron Microscopy, and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy. The utility and limitations of FACS for size separation of mAb particles and potential of in-vitro PBMC studies to rank order the immunogenic potential of various types of mAb particles is discussed
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
Kinetic Modeling of Sorbitol Hydrogenolysis over Bimetallic RuRe/C Catalyst
Sorbitol hydrogenolysis
kinetics using bimetallic RuRe catalyst
is reported based on multiple experiments in parallel batch slurry
reactors (H<sub>2</sub> pressure: 1.0–6.5 MPa, temperature:
473–503 K) to obtain concentration–time profiles. It
is observed that RuRe/C bimetallic catalysts with CaÂ(OH)<sub>2</sub> as a base promoter show significantly higher activity and selectivity
toward liquid phase products such as 1,2-propanediol, lactic acid,
ethylene glycol, and linear alcohols compared with monometallic Ru/C
catalysts and other base promoters. It is further found that sorbitol
hydrogenolysis initiates with dehydrogenation and subsequent C–C
cleavage via retro-aldolization to form smaller molecules (C<sub>2</sub>–C<sub>4</sub>). Those smaller intermediates undergo dehydration,
reorganization, and C–O cleavage to form C<sub>2</sub>–C<sub>3</sub> acids, glycols, and linear alcohols as products, which are
very similar to glycerol conversion chemistry. For the kinetic modeling,
experimental data on concentration–time profiles were obtained
using RuRe/C catalysts with CaÂ(OH)<sub>2</sub> promoter in which H<sub>2</sub> pressure, catalyst loading, and temperature were varied.
The analysis of kinetic models employed a batch slurry reactor model
with which several rate equations based on different complex multistep
reaction mechanisms were fit to the experimental data in order to
gain insights into the reaction pathways and mechanisms. Activation
energies for sorbitol hydrogenolysis to glycols and further conversion
of glycols to corresponding alcohols are found to be in the range
38 kJ/mol to 125+ kJ/mol. The kinetic model from this work provides
the framework for developing rational multiphase reactor engineering
strategies for upgrading polyol mixtures (e.g., glycerol, xylitol,
sorbitol, and mannitol) to value-added glycols and alcohols
Formation of Self-Organized Nanoporous Anodic Oxide from Metallic Gallium
This paper reports the formation of self-organized nanoporous
gallium
oxide by anodization of solid gallium metal. Because of its low melting
point (ca. 30 °C), metallic gallium can be shaped into flexible
structures, permitting the fabrication of nanoporous anodic oxide
monoliths within confined spaces like the inside of a microchannel.
Here, solid gallium films prepared on planar substrates were employed
to investigate the effects of anodization voltage (1, 5, 10, 15 V)
and H<sub>2</sub>SO<sub>4</sub> concentration (1, 2, 4, 6 M) on anodic
oxide morphology. Self-organized nanopores aligned perpendicular to
the film surface were obtained upon anodization of gallium films in
ice-cooled 4 and 6 M aqueous H<sub>2</sub>SO<sub>4</sub> at 10 and
15 V. Nanopore formation could be recognized by an increase in anodic
current after a current decrease reflecting barrier oxide formation.
The average pore diameter was in the range of 18–40 nm with
a narrow diameter distribution (relative standard deviation ca. 10–20%),
and was larger at lower H<sub>2</sub>SO<sub>4</sub> concentration
and higher applied voltage. The maximum thickness of nanoporous anodic
oxide was ca. 2 μm. In addition, anodic formation of self-organized
nanopores was demonstrated for a solid gallium monolith incorporated
at the end of a glass capillary. Nanoporous anodic oxide monoliths
formed from a fusible metal will lead to future development of unique
devices for chemical sensing and catalysis
Atom Economical Aqueous-Phase Conversion (APC) of Biopolyols to Lactic Acid, Glycols, and Linear Alcohols Using Supported Metal Catalysts
Conversion
of renewable biopolyols to value-added chemicals such
as lactic acid and glycols usually demands excess hydrogen/oxygen
or harsh reaction conditions in strong alkaline medium (220–350
°C). This unfortunately promotes significant side reactions resulting
in low carbon selectivity to liquid products, posing significant challenges
for the development of sustainable technologies. We report here a
new atom economical catalytic conversion of various biopolyols (glycerol,
xylitol, mannitol, and sorbitol) to lactic acid with glycols and linear
alcohols as co-products at much lower temperatures (115–160
°C) without external addition of either hydrogen or oxygen. Among
various metal-based catalysts (Pt, Pd, Rh, Ru, Raney Ni, Raney Co,
and Cu) evaluated, Pt/C catalyst gives the highest chemoselectivity
(S > 95%) for lactic acid, glycols, and linear alcohols at 115–160
°C. An important finding is that approximately two-thirds of
the hydrogen generated in situ via dehydrogenation of polyols over
Pt/C catalyst is efficiently utilized for the conversion of the remaining
polyols and intermediates to useful products (e.g., glycols and linear
alcohols instead of gaseous products) with the remaining available
hydrogen for use elsewhere in a biorefinery. The Pt/C catalyst is
thus multifunctional facilitating tandem dehydrogenation/hydrogenolysis
of polyols. Furthermore, it is observed that Ba<sup>2+</sup> alkali
ion promotes the activity of the Pt/C catalyst by almost 12-fold compared
to other alkali promoters such as NaOH, KOH, and CaÂ(OH)<sub>2</sub>. In addition to being the first reported study on the conversion
of C<sub>5</sub>∼C<sub>6</sub> polyols (e.g., xylitol and sorbitol)
to lactic acid at relatively low temperatures, the results also provide
new insights into the mechanism of tandem catalysis of biopolyols
conversion to value-added commodity chemicals