Understanding the interaction of concanavalin a with mannosyl glycoliposomes: A surface plasmon resonance and fluorescence study.

The specificity of carbohydrate-protein interaction is a key factor in many biological processes and it is the foundation of technologies using glycoliposomes in drug delivery. The incorporation of glycolipids in vesicles is expected to increase their specificity toward particular targets such as lectins; however, the degree of exposure of the carbohydrate moiety at the liposome surface is a crucial parameter to be considered in the interaction. Herein we report the synthesis of mannose derivatives with one or two hydrophobic chains of different length, designed with the purpose of modifying the degree of exposure of the mannose when they were incorporated into liposomes. The interaction of glycovesicles with Con A was studied using: (i) agglutination assays; measured by dynamic laser light scattering (DLS); (ii) time resolved fluorescence methods and (iii) surface plasmon resonance (SPR) kinetic measurements. DLS data showed that an increase in hydrophobic chain length promotes a decrease of liposomes hydrodynamic radius. A longer hydrocarbon chain favors a deeper insertion into the bilayer and mannose moiety results less exposed at the surface to interact with lectin. Fluorescence experiments showed changes in the structure of glycovesicles due to the interaction with the protein. From SPR measurements the kinetic and equilibrium constants associated to the interaction of ConA with the different glycolipid synthetized were determined. The combination of SPR and fluorescence techniques allowed to study the interaction of Con A with mannosyl glycovesicles at three levels: at the surface, at the interface and deeper into the bilayer.

Covalent functionalization of single-walled carbon nanotubes with polytyrosine: Characterization and analytical applications for the sensitive quantification of polyphenols.

This work reports the synthesis and characterization of single-walled carbon nanotubes (SWCNT) covalently functionalized with polytyrosine (Polytyr); the critical analysis of the experimental conditions to obtain the efficient dispersion of the modified carbon nanotubes; and the analytical performance of glassy carbon electrodes (GCE) modified with the dispersion (GCE/SWCNT-Polytyr) for the highly sensitive quantification of polyphenols. Under the optimal conditions, the calibration plot for the amperometric response of gallic acid (GA) shows a linear range between 5.0 × 10(-7) and 1.7 × 10(-4) M, with a sensitivity of (518 ± 5) m AM(-1) cm(-2), and a detection limit of 8.8 nM. The proposed sensor was successfully used for the determination of total polyphenolic content in tea extracts.

Analytical applications of glassy carbon electrodes modified with multi-wall carbon nanotubes dispersed in polyethylenimine as detectors in flow systems.

This work reports the advantages of using glassy carbon electrodes (GCEs) modified with multi-wall carbon nanotubes (CNT) dispersed in polyethylenimine (PEI) as detectors in flow injection and capillary electrophoresis. The presence of the dispersion of CNT in PEI at the electrode surface allows the highly sensitive and reproducible determination of hydrogen peroxide, different neurotransmitters (dopamine (D) and its metabolite dopac, epinephrine (E), norepinephrine (NE)), phenolic compounds (phenol (P), 3-chlorophenol (3-CP) and 2,3-dichlorophenol (2,3CP)) and herbicides (amitrol). Sensitivities enhancements of 150 and 140 folds compared to GCE were observed for hydrogen peroxide and amitrol, respectively. One of the most remarkable properties of the resulting electrode is the antifouling effect of the CNT/PEI layer. No passivation was observed either for successive additions (30) or continuous flow (for 30 min) of the compounds under investigation, even dopac or phenol. A critical comparison of the amperometric and voltammetric signal of these different analytes at bare- and PEI-modified glassy carbon electrodes and pyrolytic graphite electrodes is also included, demonstrating that the superior performance of CNT is mainly due to their unique electrochemical properties. Glassy carbon electrodes modified with CNT-PEI dispersion also show an excellent performance as amperometric detector in the electrophoretic separation of phenolic compounds and neurotransmitters making possible highly sensitive and reproducible determinations.

Electrochemical sensor for amino acids and albumin based on composites containing carbon nanotubes and copper microparticles.

This work reports on the analytical performance of composites obtained by dispersing copper microparticles and multi-wall carbon nanotubes within a mineral oil binder (CNTPE-Cu) for the determination of amino acids and albumin. The strong complexing activity of amino acids towards copper makes possible an important improvement in the sensitivity for the determination of amino acids and albumin. This new electrode permits the highly sensitive amperometric detection of amino acids, even the non-electroactive ones, at very low potentials (0.000V) and physiological pH (phosphate buffer solution pH 7.40). The response of the electrode is highly dependent on the amount of copper, demonstrating the crucial role of the metal in the analytical performance of the sensor. The best analytical performance is obtained for the electrode containing 6.0% (w/w) copper. The resulting sensor shows a fast response (7s) and a sensitivity that depends on the nature of the amino acid. The electrode surface demonstrates an excellent resistance to surface fouling, with R.S.D. of 4% for the sensitivities of 10 successive calibration plots. Albumin is determined with CNTPE-Cu using a protocol based on the accumulation of the protein for 10min at -0.100V, followed by the square-wave voltammetric analysis. The quantification of albumin concentration in lyophilized control serum gives excellent agreement with the classical spectrophotometric methodology and with the value informed for the supplier.

Carbon nanotubes for electrochemical biosensing.

The aim of this review is to summarize the most relevant contributions in the development of electrochemical (bio)sensors based on carbon nanotubes in the last years. Since the first application of carbon nanotubes in the preparation of an electrochemical sensor, an increasing number of publications involving carbon nanotubes-based sensors have been reported, demonstrating that the particular structure of carbon nanotubes and their unique properties make them a very attractive material for the design of electrochemical biosensors. The advantages of carbon nanotubes to promote different electron transfer reactions, in special those related to biomolecules; the different strategies for constructing carbon nanotubes-based electrochemical sensors, their analytical performance and future prospects are discussed in this article.

Analytical applications of a carbon nanotubes composite modified with copper microparticles as detector in flow systems.

In this work we report on the successful use of a composite prepared by dispersion of multi-wall carbon nanotubes (1-5 microm length, 20-50 nm diameter) and copper microparticles within mineral oil as detector for amino acids quantification in flow injection analysis and capillary electrophoresis. The resulting electrode displays a highly sensitive amperometric detection of amino acids, based on the copper dissolution facilitated by the strong activity of amino acids as ligands of Cu(II). The sensor makes possible the detection of amino acids, electroactive or not, at very low potentials (0.000 V) and physiological pH. A correlation between the sensitivity for the amino acids and the amount of copper within the composite is observed, demonstrating the importance of the metal in the sensor response. The best analytical performance is obtained for the electrode containing 12.0% (w/w) copper. The excellent results obtained with the carbon nanotube paste electrodes containing copper (CNTPE-Cu) as detector in flow systems makes them an interesting alternative for further analytical applications involving different bioanalytes.

An amperometric nitrate reductase-phenosafranin electrode: kinetic aspects and analytical applications.

The enzyme-catalysed reduction of nitrate was studied utilising Aspergillus niger nitrate reductase (NR) and phenosafranin in solution as the enzyme regenerator, working at lower potentials than that of the more common methyl viologen mediator. Cyclic voltammograms when enzyme, phenosafranin and substrate were together put in evidence the enzyme-catalysed reduction of nitrate, although with a relatively slow kinetics. From slope values not dependent on mediator concentration, the apparent Michaelis-Menten constant was evaluated. Analytical parameters for the enzyme-modified electrode in the presence of phenosafranin for the determination of nitrate content in water were assessed, including a recovery assay for nitrate added to a river water sample. The stability of the electrode was checked.

Supervisión y monitoreo realizado a los servicios Dots-C Sedes La Paz-Area Urbana / En

El objetivo general es la supervisión del Programa Nacional de Control de Tuberculosis,medición del avance de las metas e indicadores de proceso,y recolección de información complementaria para la implementación de la Estrategia Dots-c