161 research outputs found
Carbon surface derivatization by electrochemical reduction of a diazonium salt in situ produced from the nitro precursor
Two different surface derivation procedures have been used to modify glassy carbon electrodes based on the electrochemical reduction of diazonium cations in situ generated from the nitro precursor. The first sequential procedure completely reduces the nitro group into the corresponding amine, which is further diazotized in situ. This unique sequential procedure allows surface derivatization by species having extended conjugation as illustrated by the use of a p-nitrophenylethynyl benzene precursor. The second concerted procedure yields the diazonium cation in situ by the conversion of the nitro group into the corresponding amine in presence of all reagents required for the diazotization reaction. The major advantage of this one-pot procedure is that the diazonium cation is generated locally in close proximity to the electrode surface by rapid diazotization of the electrogenerated amine. The in situ production of diazonium cations and subsequent surface attachment is monitored using a p-nitrophenylethynyl benzene precursor bearing a catechol group. Surface coverages are determined from the cyclic voltammograms of the surface-confined catechol groups. A comparative study of the surface coverage values obtained for redox surfaces prepared with different conditions, allows optimization of the one pot procedure, leading to an efficient surface modification. (C) 2011 Elsevier B.V. All rights reserved
Wear resistant solid lubricating coatings via compression molding and thermal spraying technologies
This work combines two industrially friendly processing methods in order to create wear resistant and solid-lubricating composite coatings potentially suitable for high load applications. Layered composite coatings were fabricated over wrought stainless steel 444 (SS444) by compression molding a mixture of solid lubricant polymer, polytetrafluoroethylene (PTFE, 80 wt%), and wear resistant polymer, polyimide (PI, 20 wt%), onto iron aluminide (Fe3Al) thermal spray coatings without the need of either primers or adhesives. The fabrication process consisted of three main steps: deposition of the Fe3Al thermal spray coating onto a SS444 substrate and transfer into a metal mold; transfer, compress, and sinter mixed polymeric powder onto the thermal spray coating; and finally, sample cooling to room temperature. This method takes advantage of the high surface roughness of thermal spray coatings, which increases mechanical adhesion of slippery PTFE to the underlying metallic material. Coatings were produced with and without a small amount of graphite (5 wt%) to analyze its impact on sliding and wear properties. Unlike current coating technologies, the thickness of the coatings presented herein can be easily and quickly tailored by varying the amount of polymer powder added to the mold prior to compression or by grinding after fabrication. We produced and analyzed coatings ~1.3 mm in total thickness that portray coefficient of frictions ~0.1, similar to pure PTFE. The calculated wear rates for both coatings with and without graphite are an order of magnitude lower than what has been previously reported for coatings of similar composition. The influence of graphite on wear properties was found to be minimal due to the high content of self-lubricating PTFE yet can act as a way to lower material costs and increase the coatings load capacity
A Miniaturized Enzymatic Biosensor for Detection of Sensory-Evoked D-serine Release in the Brain
D-serine has been implicated as a brain messenger with central roles in neural signaling and plasticity. Disrupted levels of D-serine in the brain have been associated with neurological disorders, including schizophrenia, depression and Alzheimer's disease. Electrochemical biosensors are attractive tools for measuring real-time in vivo D-serine concentration changes. Current biosensors suffer from relatively large sizes (≥25 μm) making localized cellular measurements challenging, especially for single cell studies. In this work, a robust methodology for the fabrication of a reproducible miniaturized 10 μm D-serine detecting amperometric biosensor was developed. The miniature biosensor incorporated yeast D-amino acid oxidase immobilized on a poly-meta-phenylenediamine modified 10 μm Pt disk microelectrode. The biosensor offered a limit of detection of 0.361 μM (RSD < 10%) with high sensitivity (283 μA cm-2 mM-1, R2 = 0.983). The biosensor was stable for over four hours of continuous use, demonstrated a storage stability of four days and high analyte selectivity. Biosensor selectivity was validated with LC-MS and interferences with yeast D-amino acid oxidase were evaluated using drugs believed to stimulate D-serine release. Ex vivo D-serine measurements were made from Xenopus laevis tadpole brains, demonstrating the utility of the biosensors for measurements on living tissue. We observed that D-serine levels in the brain fluctuate with sensory experience. The biosensors were also used in vivo successfully. Taken together, this study addresses factors for successful and reproducible miniature biosensor fabrication for measuring D-serine in biological samples, for pharmacological evaluation, and for designing point of care devices
Corrosion of One-Step Superhydrophobic Stainless-Steel Thermal Spray Coatings
As most superhydrophobic coatings are made of soft materials, the need for harder, more robust films is evident in applications where erosional degradation is of concern. The work herein describes a methodology to produce superhydrophobic stainless-steel thermal spray coatings using the high-velocity oxygen fuel technique. Due to the use of a kerosene fuel source, a carbon-rich film is formed on the surface of the thermal spray coatings, lowering the surface energy of the high-energy metallic substrates. The thermal spray process generates a hierarchical micro-/sub-micro-structure that is needed to sustain superhydrophobicity. The effect of spray parameters such as particle velocity and temperature on the coating’s hydrophobicity state was explored, and a high particle velocity was shown to cause superhydrophobic characteristics. The coatings were characterized using scanning electron microscopy, profilometry, X-ray photoelectron spectroscopy, static water contact angle measurements, water droplet roll-off measurements, and water droplet bouncing tests. The corrosion behavior of the coatings was studied using potentiodynamic polarization measurements in order to correlate water repellency with corrosion resistance; however, all coatings demonstrated active corrosion without passivation. This study describes an interesting phenomenon where superhydrophobicity does not guarantee corrosion resistance and discusses alternative applications for such materials
Metabolic recovery of Arabidopsis thaliana roots following cessation of oxidative stress
To cope with the various environmental stresses resulting in reactive oxygen species (ROS) production plant metabolism is known to be altered specifically under different stresses. After overcoming the stress the metabolism should be reconfigured to recover basal operation however knowledge concerning how this is achieved is cursory. To investigate the metabolic recovery of roots following oxidative stress, changes in metabolite abundance and carbon flow were analysed. Arabidopsis roots were treated by menadione to elicit oxidative stress. Roots were fed with 13C labelled glucose and the redistribution of isotope was determined in order to study carbon flow. The label redistribution through many pathways such as glycolysis, the tricarboxylic acid (TCA) cycle and amino acid metabolism were reduced under oxidative stress. After menadione removal many of the stress-related changes reverted back to basal levels. Decreases in amounts of hexose phosphates, malate, 2-oxoglutarate, glutamate and aspartate were fully recovered or even increased to above the control level. However, some metabolites such as pentose phosphates and citrate did not recover but maintained their levels or even increased further. The alteration in label redistribution largely correlated with that in metabolite abundance. Glycolytic carbon flow reverted to the control level only 18 h after menadione removal although the TCA cycle and some amino acids such as aspartate and glutamate took longer to recover. Taken together, plant root metabolism was demonstrated to be able to overcome menadione-induced oxidative stress with the differential time period required by independent pathways suggestive of the involvement of pathway specific regulatory processes
The concept of "compartment allergy": prilocaine injected into different skin layers
We herein present a patient with delayed-type allergic hypersensitivity against prilocaine leading to spreading eczematous dermatitis after subcutaneous injections for local anesthesia with prilocaine. Prilocaine allergy was proven by positive skin testing and subcutaneous provocation, whereas the evaluation of other local anesthetics - among them lidocaine, articaine and mepivacaine - did not exhibit any evidence for cross-reactivity
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Scanning electrochemical microscopy studies applied to biological systems
This dissertation specifically deals with scanning electrochemical microscopy
(SECM) studies of cellular transport processes that involve ion channels or activated
transport proteins. To study biological systems, the substrate generation-tip collection
(SG-TC) mode of SECM is used. Because of the inherent difficulty in quantifying such
measurements, a two electrode system is first used to understand the general behavior of
SG-TC transients. Numerical simulations confirm that the transient currents measured in
SG-TC mode of SECM agree with the experimental behavior of simple electroactive
compounds. The influence of the ultramicroelectrode (UME) geometry on recorded and
simulated transient response is discussed. Finally, significant experimental and
theoretical differences in the feedback mode of SECM for hemispherical and disk UMEs
are presented.
This knowledge is subsequently applied to a biomimmetic system where an ion
channel is inserted in a self-assembled monolayer. The transport of thallium ions across
gramicidin ion channels is detected at a nearby hemispherical mercury UME. This transport system is a model system for real biological systems. Nevertheless, important
kinetic information about differences in the transport energy barrier between the two ends
of the gramicidin half-channel can be obtained. The small level current measured in the
above work confirmed that the SG-TC mode of SECM had the sensitivity to measure the
efflux of electroactive biological material from cells.
As such, the uptake of menadione and subsequent release of an electroactive
biological metabolite from yeast cells is also reported. The synthesis, electrochemical
characterization and detection of the menadione glutathione conjugate export from yeast
cells are discussed. Kinetic treatment of the collection currents from yeast aggregates
revealed that the uptake of menadione is the slow dominant step in the experiment.
Finally, single human liver cells are studied using SECM measurements while
exposed to cytotoxic concentrations of menadione. A determined cytotoxic dose of
menadione imposes a chemical stress on hepatocytes and leads to the export of the
menadione-glutathione conjugate via an ATP-dependent pump. The process is observed
and imaged for both isolated and differentiated cells and has some interesting biological
relevance.Chemistry and BiochemistryChemistr
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