Evaluation of screen-printed gold on low-temperature co-fired ceramic as a substrate for the immobilization of electrochemical immunoassays

Screen-printed gold (SPG, Dupont gold conductor 5734) on low-temperature co-fired ceramic (LTCC) materials (Dupont dielectric tape 951, mostly composed of alumina and silica) has been demonstrated to be a substrate for electrochemical enzyme-linked immunosorbant assays. The effect of two different cleaning treatments and the extent of nonspecific adsorption on the SPG/LTCC and plain LTCC surfaces were also evaluated. LTCC materials hold promise for constructing a new generation of devices for microelectrochemical sensing and assays. Facile fabrication in three dimensions with integrated conducting elements makes them attractive. A standard sandwich immunoassay for a model analyte, mouse IgG, was used to evaluate the LTCC materials. After the assembly of components onto chips of SPG/LTCC and plain LTCC, p-aminophenol that was generated enzymatically by the enzyme label was detected electrochemically with a separate glassy carbon electrode. Cleaning SPG/LTCC with a piranha solution (7:1 vol/vol of concentrated H2SO4/30% H2O2), traditionally used for other gold surfaces prior to SAM assembly, resulted in a notable decrease in assay signal and an increase in nonspecific adsorption when compared to cleaning with water alone. Assay components assemble specifically on plain LTCC, with only a small percent attributed to NSA. Environmental scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy reveal the tremendous chemical heterogeneity and complexity of both SPG/LTCC and plain LTCC surfaces and aid in the explanation of assay results. A 10% acetate Tween bovine serum albumin solution and an ethanolic solution of 4 mM 1-butanol eliminate assay signals originating from plain LTCC. The outcomes of these studies can now be used to achieve miniaturized electrochemical immunoassays on LTCC materials where both plain and SPG surfaces are present.     

Associative and segregative phase separations of gelatin/kappa-carrageenan aqueous mixtures

The effects of ionic strength, temperature, and pH on the phase separation behavior of type B pigskin gelatin/sodium-type kappa-carrageenan aqueous mixtures were investigated. Depending on the different combinations of temperature and sodium chloride (NaCl) concentration, the mixtures showed compatible, associative, and segregative phase separation behaviors. Additionally, a coexistence of associative and segregative (associative-co-segregative) phase separations was expected at low temperature and low NaCl concentration. These different phase separation events were observed using confocal scanning laser microscopy. Moreover, it was found that the segregative phase separation when alone is induced by the ordering of kappa-carrageenan chains, while that in the coexistence region is induced by the ordering of gelatin chains. pH had a significant effect on the associative phase separation, resulting in morphologies changing from compatible solution to liquid coacervate and further to solid precipitate with decreasing pH. These were attributed to the dramatic changes of the charge density of amphoteric gelatin during the pH decrease.     

Synthesis of poly(beta-amino ester)s with thiol-reactive side chains for DNA delivery

The safe and efficient delivery of DNA remains the major barrier to the clinical application of non-viral gene therapy. Here, we present novel, biodegradable polymers for gene delivery that are capable of simple graft modification and demonstrate the ability to respond to intracellular conditions. We synthesized poly(beta-amino ester)s using a new amine monomer, 2-(pyridyldithio)-ethylamine (PDA). These cationic, degradable polymers contain pyridyldithio functionalities in the side chains that react with high specificity toward thiol ligands. This reactivity is demonstrated using both mercaptoethylamine (MEA) and the thiol peptide RGDC, a ligand that binds with high affinity to certain integrin receptors. These two polymer derivatives displayed strong DNA binding as determined using electrophoresis and dye exclusion assays. In addition, the MEA-based polymer and plasmid DNA were shown to self-assemble into cationic complexes with effective diameters as low as 100 nm. Furthermore, this DNA binding ability was substantially reduced in response to intracellular glutathione concentrations, which may aid in DNA unpackaging inside the cell. These complexes also displayed low cellular toxicity and were able to mediate transfection at levels comparable to PEI in human hepatocellular carcinoma cells. These results suggest that PDA-based poly(beta-amino ester)s may serve as a modular platform for polymer-mediated gene delivery.     

Redox magnetohydrodynamic enhancement of stripping voltammetry: toward portable analysis using disposable electrodes, permanent magnets, and small volumes

The use of redox magnetohydrodynamics (MHD) to enhance the anodic stripping voltammetry (ASV) response of heavy metals has been investigated, with respect to achieving portability: disposable electrodes consisting of screen-printed carbon (SPC) on a low temperature co-fired ceramic (LTCC) substrate, small volumes, and permanent magnets. The analytes tested (Cd(2+), Cu(2+), and Pb(2+)) were codeposited on SPC with Hg(2+) to form a Hg thin film electrode. High concentrations of Fe(3+) were used to produce a high cathodic current which generates a significant Lorentz force in the presence of a magnetic field. This Lorentz force induces solution convection during the deposition step, enhancing the mass transport of analytes to the electrode and increasing their preconcentrated quantity in the mercury thin film. Therefore, larger ASV peaks and improved sensitivities are obtained, compared to analyses performed without a magnet. The effects on ASV signal of varying Hg(2+) concentration (0.10 and 1.0 mM), deposition time (10-600 s), and electrode surface roughness were investigated. In addition, analyses were performed using a real lake water matrix. By using the disposable LTCC-SPC working electrodes in small volumes (150 microL) and with small permanent magnets (0.78 T), peak areas were increased by 75% when compared to the signal obtained in the absence of a magnetic field. A limit of detection of 25 nM for Cd(2+) was observed with only a 1 min preconcentration time.     

Local structural order in carbonic acid polymorphs: Raman and FT‐IR spectroscopy

Two different polymorphs of carbonic acid, α‐ and β‐H₂CO₃, were identified and characterized using infrared spectroscopy (FT‐IR) previously. Our attempts to determine the crystal structures of these two polymorphs using powder and thin‐film X‐ray diffraction techniques have failed so far. Here, we report the Raman spectrum of the α‐polymorph, compare it with its FT‐IR spectrum and present band assignments in line with our work on the β‐polymorph [Angew. Chem. Int. Ed. 48 (2009) 2690–2694]. The Raman spectra also contain information in the wavenumber range ∼90–400 cm⁻¹, which was not accessible by FT‐IR spectroscopy in the previous work. While the α‐polymorph shows Raman and IR bands at similar positions over the whole accessible range, the rule of mutual exclusion is obeyed for the β‐polymorph. This suggests that there is a center of inversion in the basic building block of β‐H₂CO₃ whereas there is none in α‐H₂CO₃. Thus, as the basic motif in the crystal structure we suggest the cyclic carbonic acid dimer containing a center of inversion in case of β‐H₂CO₃ and a catemer chain or a sheet‐like structure based on carbonic acid dimers not containing a center of inversion in case of α‐H₂CO₃. This hypothesis is strengthened when comparing Raman active lattice modes at < 400 cm⁻¹ with the calculated Raman spectra for different dimers. In particular, the intense band at 192 cm⁻¹ in β‐H₂CO₃ can be explained by the inter‐dimer stretching mode of the centrosymmetric RC(OHO)₂ CR entity with ROH. The same entity can be found in gas‐phase formic acid (RH) and in β‐oxalic acid (RCOOH) and produces an intense Raman active band at a very similar wavenumber. The absence of this band in α‐H₂CO₃ confirms that the difference to β‐H₂CO₃ is found in the local coordination environment and/or monomer conformation rather than on the long range. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of an HPLC Method for Determination of Related Impurities in Prilocaine Substance

Development of a reversed phase high performance liquid chromatographic method for determination of six related impurities in prilocaine substance is reported. The test of related impurities in European Pharmacopoeia (Ph. Eur.) cannot meet the demands with the chromatographic parameters given, therefore different types of chromatographic systems and eight columns have been evaluated in the present study. A new method with a Hypercarb column was developed and validated. This method fulfils the demands in the Ph. Eur., and the validation shows that the method is selective, reproducible, linear, accurate and robust with sufficient limits of detection (0.001–0.004% of 2.5?mg prilocaine mL^?1) and quantification (0.002–0.009% of 2.5?mg prilocaine mL^?1).     

Hydrogen Bonding in Pyridine N-Oxide/Acid Systems: Proton Transfer and Fine Details Revealed by FTIR, NMR, and X-ray Diffraction

The H-bonded complexes of pyridine N-oxide (PyO) with H(2)O, acetic, cyanoacetic, propiolic, tribromoacetic, trichloroacetic, trifluoroacetic, hydrochloric, and methanesulfonic acids have been studied by FTIR and NMR spectroscopy, X-ray diffraction, and quantum chemical DFT calculations. Correlations between vibrational frequencies of the NO stretching and PyO ring modes and geometric parameters of the H-bond have been established. FTIR experiments show and DFT calculations confirm that definite discontinuity is present in the vicinity of the midpoint in the proton transfer pathway. The established correlations significantly aid in the understanding of fine effects such as the isotope (deuteration) effect, crystal-to-solution transition, or criticality of aqueous solutions induced by ionic pairs. Geometric isotope effect in the ionic H-bond aggregate of PyO·H(D)Cl was found to be extraordinary large. Measured FTIR, CP/MAS, and high-resolution (13)C NMR spectra indicate that H-bond in the PyO·HCl complex in polar solvent can potentially be more ionic than in the crystal. Vibrational modes of ionic pairs originating via proton transfer in H-bond complexes can provide new information concerning the interionic interaction and its role in the phase separation and mezo-structuring processes. The results are compared to the relevant data for PyO·HCl complex in argon matrix.     

Finite dynamic deformations of a hyperelastic,anisotropic, incompressible and prestressed tube. Applications to in vivo arteries

In this paper, we study the mechanical behavior of a prestressed tube subjected to finite dynamic deformations. The tube is assumed to be made of a hyperelastic, anisotropic and incompressible material. The analysis is carried out by using a Mooney–Rivlin stored energy function augmented with fiber reinforcements in four unidimensional orientations. A semi-analytical solution is proposed to study the radial dynamic mechanical response of an artery by using in vivo data. The optimal model parameters describing the mechanical characteristics of arterial wall microconstituents are obtained by minimizing the difference between computed and measured inner pressures over the cardiac cycle using a nonlinear regression. Theoretical and experimental results on rat carotid elastic arteries are compared in order to assess the validity of the approach by estimating differences of the model parameters and wall stresses with aging.