108 research outputs found
Differential Cyclic Voltammetry - a Novel Technique for Selective and Simultaneous Detection using Redox Cycling Based Sensors
Redox cycling (RC) is an effect that is used to amplify electrochemical signals. However, traditional techniques such as cyclic voltammetry (CV) do not provide clear insight for a mixture of multiple redox couples while RC is applied. Thus, we have developed a new measurement technique which delivers electrochemical spectra of all reversible redox couples present based on concentrations and standard potentials. This technique has been named differential cyclic voltammetry (DCV). We have fabricated micrometer-sized interdigitated electrode (IDE) sensors to conduct DCV measurements in mixtures of 1mM catechol and 4mM [Ru(NH3)6]Cl3. To simulate the electrochemical behavior of these sensors we have also developed a finite element model (FEM) in ComsolÂŽ. The\ud
experimental data corresponds to the calculated spectra obtained from simulations. Additionally, the measured spectra can be used to easily derive standard potentials and concentrations simultaneously and selectively.\u
Toward a hydrogen peroxide sensor for exhaled breath analysis
In this contribution a chip-integrated amperometric sensor for the detection of H2O2 in exhaled breath condensate (EBC) is reported. The electrode chip is characterized, and detection of H2O2 in an aqueous phase is shown by means of cyclic voltammetry (CV) and amperometry. Variation of conditions such as the composition of the supporting electrolyte largely influences the obtained electrochemical response. Also it is found that electrochemical pretreatment of the platinum working electrode aiming at surface oxidation improves the detection limit of the sensor. Finally, the device is applied to measurement of H2O2 in the gaseous phase
Ab initio quantum mechanical simulations confirm the formation of all postulated species in ionic dissociation
A single sodium chloride molecule in aqueous solution was simulated by the ab initio quantum mechanical charge field-molecular dynamics (QMCF-MD) approach. During a series of simulations the solvated molecule (CIP), dissociated solvated ions and - most noticeably - a solvent separated ion pair (SSIP) were observed and the structural and dynamical characteristics of these systems were investigated. In addition to a detailed structural analysis of the observed species, vibrational spectra and charge distributions were calculated to elucidate the mechanism of the NaCl dissociation
On ultrasound-induced microbubble oscillation in a capillary blood vessel and its implications for the bloodâbrain barrier
The breakup of intravascular microbubbles and its impact on the endothelium
Encapsulated microbubbles (MBs) serve as endovascular agents in a wide range of medical ultrasound applications. The oscillatory response of these agents to ultrasonic excitation is determined by MB size, gas content, viscoelastic shell properties and geometrical constraints. The viscoelastic parameters of the MB capsule vary during an oscillation cycle and change irreversibly upon shell rupture. The latter results in marked stress changes on the endothelium of capillary blood vessels due to altered MB dynamics. Mechanical effects on microvessels are crucial for safety and efficacy in applications such as focused ultrasound-mediated blood-brain barrier (BBB) opening. Since direct in vivo quantification of vascular stresses is currently not achievable, computational modelling has established itself as an alternative. We have developed a novel computational framework combining fluid-structure coupling and interface tracking to model the nonlinear dynamics of an encapsulated MB in constrained environments. This framework is used to investigate the mechanical stresses at the endothelium resulting from MB shell rupture in three microvessel setups of increasing levels of geometric detail. All configurations predict substantial elevation of up to 150Â % for peak wall shear stress upon MB breakup, whereas global peak transmural pressure levels remain unaltered. The presence of red blood cells causes confinement of pressure and shear gradients to the proximity of the MB, and the introduction of endothelial texture creates local modulations of shear stress levels. With regard to safety assessments, the mechanical impact of MB breakup is shown to be more important than taking into account individual red blood cells and endothelial texture. The latter two may prove to be relevant to the actual, complex process of BBB opening induced by MB oscillations
Capillary micromechanics: Measuring the elasticity of microscopic soft objects
We present a simple method for accessing the elastic properties of
microscopic deformable particles. This method is based on measuring the
pressure-induced deformation of soft particles as they are forced through a
tapered glass microcapillary. It allows us to determine both the compressive
and the shear modulus of a deformable object in one single experiment.
Measurements on a model system of poly-acrylamide microgel particles exhibit
excellent agreement with measurements on bulk gels of identical composition.
Our approach is applicable over a wide range of mechanical properties and
should thus be a valuable tool for the characterization of a variety of soft
and biological materials
Deep blue polymer light emitting diodes based on easy to synthesize, non-aggregating polypyrene
Deep blue polymer light emitting diodes based on easy to synthesize, non-aggregating polypyrene
Deep blue polymer light emitting diodes based on easy to synthesize, non-aggregating polypyrene
Solution, Crystal and in Silico Structures of the Organometallic Vitamin B 12 âDerivative Acetylcobalamin and of its Novel RhodiumâAnalogue Acetylrhodibalamin
The natural vitamin B12âderivatives are intriguing complexes of cobalt that entrap the metal within the strikingly skewed and ringâcontracted corrin ligand. Here, we describe the synthesis of the Rh(III)âcorrin acetylrhodibalamin (AcRhbl) from biotechnologically produced metalâfree hydrogenobyric acid and analyze the effect of the replacement of the cobaltâcenter of the organometallic vitamin B12âderivative acetylcobalamin (AcCbl) with its groupâIX homologue rhodium, to give AcRhbl. The structures of AcCbl and AcRhbl were thoroughly analyzed in aqueous solution, in crystals and by in silico methods, in order to gain detailed insights into the structural adaptations to the two homologous metals. Indeed, the common, nucleotideâappended corrinâligand in these two metal corrins features extensive structural similarity. Thus, the rhodiumâcorrin AcRhbl joins the small group of B12âmimics classified as âantivitamins B12â, isostructural metal analogues of the natural cobaltâcorrins that hold significant potential in biological and biomedical applications as selective inhibitors of key cellular processes
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