Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: a review.

The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.

Poly(brilliant green) and poly(thionine) modified carbon nanotube coated carbon film electrodes for glucose and uric acid biosensors.

Poly(brilliant green) (PBG) and poly(thionine) (PTH) films have been formed on carbon film electrodes (CFEs) modified with carbon nanotubes (CNT) by electropolymerisation using potential cycling. Voltammetric and electrochemical impedance characterisation were performed. Glucose oxidase and uricase, as model enzymes, were immobilised on top of PBG/CNT/CFE and PTH/CNT/CFE for glucose and uric acid (UA) biosensing. Amperometric determination of glucose and UA was carried out in phosphate buffer pH 7.0 at -0.20 and +0.30 V vs. SCE, respectively, and the results were compared with other similarly modified electrodes existing in the literature. An interference study and recovery measurements in natural samples were successfully performed, indicating these architectures to be good and promising biosensor platforms.

Poly(neutral red) based hydrogen peroxide biosensor for chromium determination by inhibition measurements.

Amperometric hydrogen peroxide enzyme inhibition biosensors based on horseradish peroxidase (HRP) immobilised on electropolymerised neutral red (NR) or directly on the surface of carbon film electrodes (CFE) have been successfully applied to the determination of toxic Cr(III) and Cr(VI). Parameters influencing the performance of the biosensor including the enzyme immobilisation method, the amount of hydrogen peroxide, applied potential and electrolyte pH were optimised. The inhibition of horseradish peroxidase by the chromium species was studied under the optimised conditions. Results from the quantitative analysis of chromium ions are discussed in terms of detection limit, linear range and sensitivity. The HRP kinetic interactions reveal mixed binding of Cr(III) with I50=3.8µM and inhibition binding constant Ki=11.3µM at HRP/PNR/CFE biosensors and uncompetitive binding of Cr(VI) with I50=3.9µM and Ki=0.78µM at HRP/CFE biosensors in the presence of H2O2 substrate. Interferences from other heavy metal ions were studied and the inhibition show very good selectivity towards Cr(III) and Cr(VI).

Response surface methodology and Taguchi approach to assess the combined effect of formulation factors on minocycline delivery from collagen sponges.

An important aspect to be considered in the healing of acute or chronic cutaneous wounds is the associated potential infection management. Collagen, the most abundant protein of the extracellular matrix, with proven properties in wounds healing and tissues regeneration, is one of the most widely used biopolymers as carrier matrix for controlled drug delivery systems. For this reason, the purpose of the current paper is the development of some minocycline-loaded collagen topical sponges uncross-linked and cross-linked with glutaraldehyde, obtained by lyophilization of appropriate hydrogels prepared according to the 3-factor, 3-level face-centered central composite design. The determination of drug delivery from the sponges was performed by assessment of some physicochemical parameters involved in this complex process: sponges surface wettability, swelling ratio and the percentage of minocycline released from the sponges. The application of the response surface methodology allowed the setting of the formulation parameters optimum ranges, which ensure an adequate minocycline release to the application site. The design robustness was checked using the signal-to-noise ratio performance indicator. The optimum collagen-minocycline sponges determined based on the statistical screening technique could be suitable for topical drug delivery in infected wounds healing with moderate to high exudate.

A novel amperometric sensor for ascorbic acid based on poly(Nile blue A) and functionalised multi-walled carbon nanotube modified electrodes.

A new type of modified electrode sensor for ascorbic acid has been prepared by deposition of multi-walled carbon nanotubes (MWCNT) and poly(Nile blue A) on the surface of glassy carbon electrodes. Nile blue A was electropolymerised either beneath (directly on glassy carbon) or onto the MWCNT layer by potential cycling in phosphate buffer solution at pH 6.0. Characterisation of the modified electrodes was carried out by cyclic voltammetry and electrochemical impedance spectroscopy. Quantitative determination of ascorbate was achieved by cyclic voltammetry and fixed potential amperometry in phosphate buffer solution at pH 5.3. The modified electrodes exhibited good sensitivity, wide linear range, a detection limit of 1.6 µM and good stability, showing that they can be used as sensors for ascorbic acid. There is no interference from compounds commonly found in clinical and pharmaceutical samples and the determination of ascorbic acid in commercial tablet samples was successfully performed.

Design of a new hypoxanthine biosensor: xanthine oxidase modified carbon film and multi-walled carbon nanotube/carbon film electrodes.

A new and simple-to-prepare hypoxanthine biosensor has been developed using xanthine oxidase (XOD) immobilised on carbon electrode surfaces. XOD was immobilised by glutaraldehyde cross-linking on carbon film (CF) electrodes and on carbon nanotube (CNT) modified CF (CNT/CF). A comparison of the performance of the two configurations was carried out by the current response using amperometry at fixed potential; the best characteristics being exhibited by XOD/CNT/CF modified electrodes. The effects of electrolyte pH and applied potential were evaluated, and a proposal is made for the enzyme mechanism of action involving competition between regeneration of flavin adenine dinucleotide and reduction of hydrogen peroxide. Under optimised conditions, the determination of hypoxanthine was carried out at -0.2 V vs. a saturated calomel electrode (SCE) with a detection limit of 0.75 µM on electrodes with CNT and at -0.3 V vs. SCE with a detection limit of 0.77 µM on electrodes without CNT. The applicability of the biosensor was verified by performing an interference study, reproducibility and stability were investigated, and hypoxanthine was successfully determined in sardine and shrimp samples.

Design and optimization of some collagen-minocycline based hydrogels potentially applicable for the treatment of cutaneous wound infections.

Topical delivery systems for the treatment of different infected cutaneous wounds based on natural biopolymers are widely studied. The development of some topical hydrogels with type I collagen and minocycline by the experimental design technique, based on response surface methodology and Taguchi's approach, and the evaluation of their kinetic properties is presented. The concentrations of polymer, drug and cross-linking agent were selected as independent variables for the face centered composite design and low, medium and high concentration as variation levels for each factor. Minocycline kinetic release was investigated using a modified Franz diffusion cell. The drug release followed the Higuchi model. Three formulations having optimal minocycline release profiles were selected. They can be used as potential drug topical release systems for the treatment of infected cutaneous tissue.

Enzyme immobilisation on electroactive nanostructured membranes (ENM): optimised architectures for biosensing.

Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H(2)O(2), the product of the oxidase enzymatic reaction, at 0.0 V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1 microM and an apparent Michaelis-Menten constant of 0.20mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples.

Carbon film electrodes for oxidase-based enzyme sensors in food analysis.

Carbon film resistor electrodes have been evaluated as transducers for the development of multiple oxidase-based enzyme electrode biosensors. The resistor electrodes were first modified with Prussian Blue (PB) and then covered by a layer of covalently immobilized enzyme. Electrochemical impedance spectroscopy was used to characterize the interfacial behaviour of the Prussian Blue modified and enzyme electrodes; the spectra demonstrated that the access of the substrates is essentially unaltered by application of the enzyme layer. These enzyme electrodes were used to detect the substrate of the oxidase (glucose, ethanol, lactate, glutamate) via reduction of hydrogen peroxide at +50mV versus Ag/AgCl in the low micromolar range. Response times were 1-2min. Finally, the glucose, ethanol and lactate electrochemical biosensors were used to analyse complex food matrices-must, wine and yoghurt. Data obtained by the single standard addition method were compared with a spectrophotometric reference method and showed good correlation, indicating that the electrodes are suitable for food analysis.

[Molecular analysis of the parental origin of trisomy in two families with two children having regular trisomy 21]. / Analyse moléculaire de l'origine parentale de la trisomie dans deux fratries comportant deux enfants atteints de trisomie 21 libre.

In order to investigate the parental origin of the trisomy in two families with two free trisomy 21 affected siblings, cytogenetic and molecular analyses were performed. In each case the parental origin was the same for both patients. In one of the families an association between the concordance of the paternal origin of the trisomy and the existence of mosaicism in the blood was established. The various etiologies which may account for recurrence are discussed.

Ring-14 and trisomy 14q in the same child.

The case of a male child with three cell lines is described: one cell line with ring chromosome 14, another trisomic for 14q, due to a derived metacentric 14q;14q, and a third one with a normal male karyotype. The clinical findings are compatible with those of the r(14) syndrome.

[Outbreak of Q fever in a municipal abattoir]. / Episod de febra Q într-un abator municipal.

The present paper reports on a Q fever outbreak of 149 cases in a municipal slaughter house focus. The diagnosis was established by clinical, epidemiological, radiologic and laboratory investigations. The route of transmission was air-borne from the sick animals (not detected at the veterinary control) to man. A closer cooperation is recommended between the human and veterinary health services, for early detection of the cases, their prevention and control. The authors suggest the need to immunize the personnel exposed to the risk of contamination (zoo technical units, slaughter house personnel, etc.).