Electrodos de PVC/TTF-TCNQ modificados. Aplicación como sensores y biosensores electroquímicos

En este trabajo de Tesis Doctoral, se estudia el desarrollo de nuevos electrodos, basados en la modificación del electrodo compósito PVC/TTF-TCNQ, mediante nanopartículas de oro. Se pretende que estos nuevos electrodos sean susceptibles de ser empleados como sensores y/o biosensores electroquímicos, para la detección de analitos de interés. De ellos, se han elegido para su determinación la glucosa, el paracetamol y los compuestos fenólicos presentes en los vinos. La Tesis Doctoral está estructurada en cinco capítulos: Introducción, Experimental, Resultados y Discusión, Conclusiones y Anexo. En la Introducción, se hace una revisión de los conceptos más generales, como son definición, clasificación y aplicación de las moléculas orgánicas conductoras, definición y clasificación de sensores químicos y biosensores, descripción de las características de los electrodos compósitos, nanopartículas metálicas y electrodos modificados con nanopartículas. En este capítulo, se incluye, también, una descripción de las técnicas electroquímicas empleadas en está memoria. En el Capítulo Experimental, se describen los aspectos técnicos del los diferentes montajes empleados, así como los procedimientos empleados para la síntesis de los diferentes electrodos empleados en este trabajo. En el Capítulo Resultados y Discusión, se describen y comentan los resultados experimentales, obtenidos para un sensor de paracetamol y para dos biosensores, uno de glucosa y otro de compuestos fenólicos, basados en los nuevos electrodos desarrollados. En el Capítulo Conclusiones, se destacan los hechos más relevantes, obtenidos a partir de los resultados experimentales. Para finalizar, en el Anexo, se muestras los artículos derivados de esta Memoria, así como las comunicaciones a congresos que han derivado de este trabajo

Electrocatalytic Oxidation of Acetaminophen on a PVC/TTF-TCNQ Composite Electrode Modified by Gold Nanoparticles: Application as an Amperometric Sensor

This work shows the electrocatalytic activity towards the oxidation of acetaminophen of a composite electrode PVC/TTF-TCNQ modified with gold nanoparticles. Owing to a good linear relationship between acetaminophen concentration and current response at lower oxidation potential it is proposed as a new alternative for amperometric determination of acetaminophen. Besides the good catalytic activity (Eapp = 0.425 V), the proposed sensor shows high reproducibility, long-term stability, low cost and can be used both in batch and in FIA systems. In batch, it was obtained a linear range for acetaminophen over a range of 1 to 800 μM with a detection limit of 0.66 μM and a correlation coefficient of 0.997 with a slope (sensitivity) of 53 mA M-1. In FIA, a sensitivity of 9.9 ± 0.15 mA M-1 and a linear regression coefficient (r) of 0.999 were obtained for a linear range for acetaminophen between 1 to 800 μM. The detection limit (s/n = 3) was 8.9 μM

New Biosensor for Phenols Compounds Based on Gold Nanoparticle-Modified PVC/TTF-TCNQ Composite Electrode

A gold nanoparticle-modified PVC/TTF-TCNQ composite electrode with tyrosinase enzyme is proposed as electrochemical biosensor for detecting phenolic compounds in musts and wines samples using phenol and catechol as standards. The work potential was 0 V both in batch and in FIA system (linear range from 0.6 μM up to 10.0 μM), with a detection limit of 7.9 x 10-7 M for phenol and 6.43 x 10-7 M for catechol. The good correlation between the results obtained with the biosensor and those achieved with the Folin–Ciocalteu reference method enables that it can be used for rapid and almost automated estimation of the “total phenolics” and “high antioxidant” fraction of must and commercial wines

Electrodo compósito PVC/TTF-TCNQ modificado con nanopartículas de oro: aplicación para la determinación amperométrica de Paracetamol

II Encuentro sobre nanociencia y nanotecnología de investigadores y tecnólogos de la Universidad de Córdoba. NANOUC

Surface Protection of Quaternary Gold Alloys by Thiol Self-Assembled Monolayers

This work deals with a physical and chemical surface characterization of quaternary 18K, 14K, and 9K gold alloys and pure polycrystalline gold substrates. Surface microstructure and composition are evaluated by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence spectroscopy. Corrosion resistance of 18K gold alloys is explored by potentiodynamic polarization showing the influence of the manufacturing process on materials fabricated as plates and wires. The research is also in the framework of one of the most common strategies on the modification of metallic surface properties, i.e., the building of self-assembled monolayers (SAM) from organic thiols. The metal affinity of the head group to produce the coating of the substrate by covalent binding is approached by using thiol compounds with different molecular structures and functional group chemistries exposed to an electrolyte solution. Therefore, a comparative study on the surface protection of a quaternary 18K gold alloy and pure gold substrates by SAMs of 6-mercaptopurine (6MP), 1-decanethiol (DT), and 11-mercaptoundecanoic acid (MUA) has been carried out. Surface modification and SAM organization are followed by cyclic voltammetry (CV), and the behavior of the double layer of the electrode–electrolyte interface is evaluated by electrochemical impedance spectroscopy (EIS). The study of these materials allows us to extract fundamental knowledge for its potential application in improving the bioactive properties of different jewelry pieces based on 18K gold alloys

Development of a method for the evaluation of comptences acquisition and its comparison with the tradicional evaluation system in subjects of Chemistry Degree

Un aspecto diferencial de la enseñanza de Grado en el Espacio Europeo de Enseñanza Superior (EEES), recogido en el Marco Español de Cualificaciones (MECES), es la definición de programas formativos que implican conocimientos y competencias. En este trabajo se han preparado rúbricas para evaluar las competencias a adquirir por el alumnado en dos asignaturas del Grado en Química. Las rúbricas diseñadas permiten dividir el conjunto de competencias en elementos diferenciados que se pueden evaluar diseñando y seleccionando actividades apropiadas. En esta herramienta se definen indicadores escalados para determinar el nivel alcanzado en cada competencia. Los resultados obtenidos con la aplicación de las rúbricas han sido correlacionados con los obtenidos en la evaluación habitual. Se propone así un método de trabajo flexible y dinámico para mejorar el proceso de evaluación.A differential aspect of the teaching of Degree in the European Higher Education Area (EHEA), included in the Spanish Qualifications Framework (MECES), is the definition of training programs that involve knowledge and skills. In this paper, rubrics have been prepared to evaluate the competences to be acquired by the students in two subjects of the Degree in Chemistry. The designed rubrics allow dividing the set of competences into differentiated elements that can be evaluated by designing and selecting appropriate activities. In this tool, scaled indicators are defined to determine the level reached in each competence. The results obtained with the application of the rubrics has been correlated with those obtained in the usual evaluation. A work method that is flexible and dynamic to improve the evaluation process is proposed

Influence of Patterning in the Acid–Base Interfacial Properties of Homogeneously Mixed CH3- and COOH-Terminated Self-Assembled Monolayers

The acid/base interfacial behavior of mixed self-assembled monolayers (SAMs) of 1-decanethiol (DT) and 11-mercaptoundecanoic acid (MUA) formed on gold from a micellar medium has been characterized by electrochemical impedance spectroscopy (EIS) and infrared reflection-absorption spectroscopy (IRRAS) titration experiments as a function of their surface composition. The surface composition is determined from the interfacial capacitance of the SAMs that behave as a dielectric medium of the expected thickness for well-organized layers. The interaction parameter and the apparent and the intrinsic surface pKa values of these pH-responsive SAMs are obtained by fitting the EIS and IR titration curves to the 1-pK model. The shift in the surface pKa while decreasing the MUA surface fraction resembles the behavior of homogeneously mixed systems. The trends observed can be explained by the lowering of intermolecular in-plane repulsive interactions between neighboring MUA molecules and by the local solvation and hydrophobic effects when the MUA domains decrease below a critical size and the terminal groups are probably titrated at domain boundaries, small arrangements, or even isolated. The transition between both scenarios and the formation of hydrogen bonding interactions upon a structural reorganization are conditioned by the heterogeneity in the size distribution of MUA and DT molecular domains which depends on the formation conditions of the SAMs. All together it is demonstrated to play a role in the acid/base properties of these monolayers which has a direct implication in the proper design of interfacial devices based on organic molecular junctions or biomolecular assemblies

Characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on gold electrodes

The modification of surfaces by polyethylene glycol (EGn) is an approach used to reduce the antifouling effects of these materials in a biological medium. It has been found that the packing density and conformational order of these molecules in the films are crucial for the inhibition of unspecific protein adsorption. In this work, we present a study of the formation and characterization of a self-assembled monolayer of O-(2-Mercaptoethyl)-O′-methyl hexa(ethylene glycol) (EG7-SAM) on either poly-oriented or Au(111) single crystal surfaces. The final properties of the formed EG7-SAMs are studied by examining the reductive desorption process as well as the electronic and ionic blocking behavior of these layers, under different experimental conditions, by using cyclic voltammetry and electrochemical impedance spectroscopy. Additional information of the structure, composition and organization is obtained by absorption-reflection infrared and X ray photoelectron spectroscopies and contact angle measurements. In contrast to the behavior observed with alkanethiols, the EG7-SAM shows the best final organization at a modification time of 1h. The antifouling properties of this EG7-SAM against the adsorption of the bovine serum albumin protein in a phosphate saline medium, has been evidenced by using the electrochemical quartz crystal microbalance technique

Electrochemical evaluation of the grafting density of self-assembled monolayers of polyethylene glycol of different chain lengths formed by the grafting to approach under conditions close to the cloud point

Grafting densities of polymers on gold surfaces are important parameters that inform about the chain conformation adopted by the chains, either mushroom or brush conformation. Most of the literature reports on this topic are based on ellipsometry measurements with other few results obtained from surface plasmon resonance or quartz crystal microbalance. In this work, we report the use of cyclic voltammetry of the reductive desorption (RD) process of mercapto-polyethylene glycol self-assembled monolayers (EGn-SAMs) to get the grafting densities of these polymers with different chain lengths (c.a. EG136, EG45 and EG18). When the EGn-SAMs are formed from aqueous solutions where the polymer chains are highly hydrated, an excess of charge density is obtained that apart from the capacitive contribution found in these processes, include an extra charge due to the hydrogen evolution reaction (HER) produced by the high ratio of water contained in the film that reduces concomitantly with the SAM RD process. However, preparing the EGn-SAM in the presence of high salt concentrations that lowers the water content within the chains, that is, using the cloud point strategy, very realistic grafting density values are obtained. The RD profiles of the EGn-SAMs completely change from a broad peak with high charge density to a structured peak that allows us the determination of grafting density values. Capacitance curves and the behavior of the electrochemical process of the Fe(CN)63-/4- redox pair in the presence of the films are also in agreement with the CV results. The grafting density values obtained by this methodology are higher than those reported for these SAMs by using other techniques but agree with the footprints expected for these chains when organized in a brush conformation. Moreover, they also are close to the values obtained by thermogravimetric analysis of the same films built on gold nanoparticles that behave as planar surfaces

Self-assembled monolayers of O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) (EG7-SAM) on gold electrodes. Effects of the nature of solution/electrolyte on formation and electron transfer blocking characteristics

The self-assembly of O-(2-Mercaptoethyl)-O’-methyl-hexa(ethylene glycol) (EG7) on gold substrates produces monolayers whose structure should depend primarily on the solvents used for their formation. Although this should be also the case for any self-assembled monolayer (SAM) system, the presence of oxygen atoms in the EG7 chains brings about specific interactions with the solvent molecules other than just the van der Waals interactions taking place with alkanethiols. In this work we investigate the effects of the nature of the solutions for EG7-SAM formation in the reductive desorption processes using gold substrates either polycrystalline or single crystal electrodes. The patterns obtained in polycrystalline substrates are compared to the peaks observed at gold single crystal electrodes and it has been found that the main peaks correspond to the molecules desorbed from the different gold facets contained in the polycrystalline substrate. These single peaks are in fact composed of at least two contributions that can be explained as the presence of domains where the EG7 molecules are organized with different orientations, giving place to intermolecular interactions of different magnitude. The blocking properties of these films are strongly determined by the nature of the electrolyte used for the analysis and not by the solvent used in their formation. Although no experimental evidence of the specific interaction and/or retention inside the film of Na+ or phosphate or both ions is obtained, a specific effect that accounts for an electron transfer rate constant of an order of magnitude lower than the obtained with other electrolytes is observed. These results can contribute to increase the understanding of the relationship between the EG7-SAMs structure and functionalities