Assessment of bone structure and acoustic impedance in C3H and BL6 mice using high resolution scanning acoustic microscopy

Two hundred-MHz time-resolved scanning acoustic microscopy was applied for the investigation of acoustic and structural bone properties of mice from two inbred strains. Transverse sections of femur taken from 5 C57BL/6J@Ico and 5 C3H/HeJ@Ico mice were explored. Both strains had the same bone diameter, but the C3H/HeJ@Ico mice had greater cortical thickness, smaller cancellous diameter, and greater acoustic impedance values than C57BL/6J@Ico mice. The strong differences in the measured acoustic impedances among the two inbred strains indicate that the impedance is a good parameter to detect genetic variations of the skeletal phenotype in small animal models.     

Study of tryptophan enantiomer binding to a teicoplanin-based stationary phase using the perturbation technique. Investigation of the role of sodium perchlorate in solute retention and enantioselectivity

The retention of D,L-tryptophan enantiomers on an immobilized teicoplanin column was investigated in relation to the mobile phase sodium perchlorate concentration using the perturbation method to determine the solute distribution isotherms. From the experimental data, it appeared that the bi-Langmuir model was able to describe D- and L-enantiomer retention on the immobilized selector over the salt concentration range. An increase in the apparent enantioselectivity with an increase in sodium perchlorate concentration was observed. The chiral recognition enhancement was governed by (i) an increase in the difference of the adsorption constants for binding to the high-affinity site (aglycone pocket) between the two enantiomers and (ii) enhancement of the number of aglycone chiral regions interacting with D-tryptophan. It is suggested that an ion-pair formation mechanism between perchlorate and solute and/or selector is responsible for this behavior. In addition, this work shows that additional secondary sites on the teicoplanin surface are involved in the apparent enantioselectivity at low sodium perchlorate concentrations.     

Displacement study on a vancomycin-based stationary phase using N-acetyl-D-alanine as a competing agent

The analysis of the binding data of D,L-dansyl amino acids on a vancomycin stationary phase is investigated in relation to the addition of N-acetyl-D-alanine in the mobile phase. This eluent additive acts as a specific competing agent for the aglycone pocket of the immobilized chiral selector. A model taking into account both stereoselective and nonstereoselective interactions between the solutes and the stationary phase is used to fit the experimental data. From the results, the theoretical approach is considered to be adequate to describe the competing agent dependence on solute retention. To the best of our knowledge, this report constitutes the first example of a displacement study on a macrocyclic antibiotic stationary phase. This work shows that dansyl amino acids bind to the active aglycone pocket of the selector and that this interaction is enantioselective. The results also demonstrate that additional enantioselective sites at the vancomycin surface are involved in the chiral discrimination of these solutes.     

Determination of free and conjugated normetanephrine and metanephrine in human plasma by high-performance liquid chromatography with electrochemical detection

A simple method for the simultaneous assay of normetanephrine and metanephrine (both free and conjugated) in human plasma by high-performance liquid chromatography with electrochemical detection has been developed. The hydrolysed plasma is purified on a Dowex 50 H+ column, and the methoxylated amines are eluted with ammonia-methanol. The methoxyamines are assayed using a dual-series electrode arrangement with differential current measurement. This system greatly improves the assay specificity toward endogenous or exogenous metabolites and drugs. The high sensitivity of the method enables the determination in normal subjects of levels of normetanephrine and metanephrine.     

Effect of temperature on DNA fractionation in slalom chromatography

Slalom chromatography is an alternative chromatographic procedure for the analysis of relatively large double-stranded DNA molecules and is based on a hydrodynamic principle. The retardation of the DNA fragments from the cleavage of the Lambda DNA by the KpnI restriction enzyme was studied using an acetonitrile-phosphate buffer as a mobile phase (flow rate equal to 0.3 ml/min) and a C1 column as a stationary phase at various temperatures. It was shown that the temperature constituted an important parameter for the separation of the DNA fragments in slalom chromatography. The DNA hydrodynamic behavior with the temperature was related to the variation in the fluid viscosity and the modification of the elastic properties of the biopolyrner.     

Effects of Adsorbed Polyaniline on Redox Processes on As(2)O(3) Surfaces

Polyaniline deposited on As(2)O(3) surface resulted in a new material, which was characterized by infrared spectoscopy, thermogravimetry, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and cyclic voltammetry. The mass percentage of polymer deposited on oxide surface is approximately 13%. The scanning electron microscopy images as well as the X-ray diffraction patterns provided conclusive evidence that the oxide surface is coated by the polymer. The cyclic voltammograms of the polyaniline adsorbed on As(2)O(3) surface showed that the adsorbate exerts remarkable effects on redox processes on this oxide. The pure oxide exhibited two oxidation/reduction peaks at 0.25/-0.06 and 0.47/-0.25 V attributed tentatively to the processes As(2)O(3)(s)+6H(+)+6e(-)=2As(s)+3H(2)O and As(s)+3H(+)+3e(-)=AsH(3)(g), respectively. The polyaniline-coated sample exhibited a better-defined voltammogram in which the first oxidation peak of the oxide had its intensity increased about four times. Copyright 2000 Academic Press.     

Optimization of the structure-switching aptamer-based fluorescence polarization assay for the sensitive tyrosinamide sensing

In this paper, a structure-switching aptamer assay based on a fluorescence polarization (FP) signal transduction approach and dedicated to the L-tyrosinamide sensing was described and optimized. A fluorescently labelled complementary strand (CS) of the aptamer central region was used as a probe. The effects of critical parameters such as buffer composition and pH, temperature, aptamer:CS stoichiometry, nature of the dye (Fluorescein (F) or Texas Red (TR)) and length of the CS (15-, 12-, 9- and 6-mer) on the assay analytical performances were evaluated. Under optimized experimental conditions (10 mM Tris-HCl, 5 mM MgCl(2) and 25 mM NaCl, pH 7.5 temperature of 22°C and stoichiometry 1:1), the results showed that, for a 12-mer CS, the F dye moderately increased the method sensitivity in comparison to the TR label. The F labelled 9-mer CS, however, did not allow the hybrid formation with the functional nucleic acid, thus emphasizing the importance of the nature of the fluorophore. In contrast, the same 9-mer CS labelled with the TR dye was able to effectively associate with the aptamer and was easily displaced upon target binding as demonstrated by a significant improvement of the sensitivity and a detection limit of 250 nM, comparable to those reported with direct aptasensing methods. The present study demonstrates that not only the CS length but also the nature of the dye played a preponderant role in the performance of the structure-switching aptamer assay, highlighting the importance of interdependently controlling these two factors for an optimal FP-based sensing platform.     

Microfluidic channel with embedded SERS 2D platform for the aptamer detection of ochratoxin A

A selective aptameric sequence is adsorbed on a two-dimensional nanostructured metallic platform optimized for surface-enhanced Raman spectroscopy (SERS) measurements. Using nanofabrication methods, a metallic nanostructure was prepared by electron-beam lithography onto a glass coverslip surface and embedded within a microfluidic channel made of polydimethylsiloxane, allowing one to monitor in situ SERS fingerprint spectra from the adsorbed molecules on the metallic nanostructures. The gold structure was designed so that its localized surface plasmon resonance matches the excitation wavelength used for the Raman measurement. This optofluidic device is then used to detect the presence of a toxin, namely ochratoxin-A (OTA), in a confined environment, using very small amounts of chemicals, and short data acquisition times, by taking advantage of the optical properties of a SERS platform to magnify the Raman signals of the aptameric monolayer system and avoiding chemical labeling of the aptamer or the OTA target.

Detecting Alzheimer's disease biomarkers: From antibodies to new bio-mimetic receptors and their application to established and emerging bioanalytical platforms – A critical review

The failure of therapeutic treatment of Alzheimer's disease (AD) patients can be related to the late onset of symptoms and, consequently, to a delayed pharmacological aid to counteract neurodegenerative progression. This is coupled to the fact that the diagnosis based on clinical criteria alone introduces high misdiagnosis rate. The availability of assessed biomarkers is therefore of crucial importance not only to counteract late diagnosis, but also to manage patients at high risk of AD development eligible for novel therapies. At the present time, amyloid-β peptides (Aβ_1-40 and Aβ_1-42 isoforms), alone or in combination with Tau protein (total and phosphorylated forms (p-tau)) constitute reliable AD biomarkers and result highly predictive of progression to AD dementia in patients with mild cognitive impairment (MCI), the earliest clinical presentation of AD. Improvement of existing diagnostic tools must take advantage of innovative bioanalytical approaches. In this review, starting from commercially available diagnostic platforms based on antibodies as recognition elements, we intended to provide a double point of view on the issue: 1) progresses achieved on innovative bioanalytical platforms (mainly sensors and biosensors) by using antibodies as consolidated receptors; 2) advance on promising bio-mimetic receptors alternative to antibodies in AD research, and their applications on conventional or innovative analytical platforms. In particular, we first focused on optical- (Propagating and Localized Surface Plasmon Resonance, named here SPR and LSPR) and electrochemical (voltammetric and impedimetric) transduction principles. Together with bioanalytical assays for AD biomarkers quantification, works aimed to investigate and understand their behavior, characteristics, and roles will also be considered in the discussion.