(Bio)analytical platforms based on the use of functionalized carbon nanotubes

Trabajo presentado al Eurosensors, celebrado en Freiburg (Alemania) del 6 al 9 de septiembre de 2015.Peer reviewe

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 isthe foundation of technologies using glycoliposomes in drug delivery. The incorporation of glycolipidsin 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 beconsidered in the interaction. Herein we report the synthesis of mannose derivatives with one or twohydrophobic chains of different length, designed with the purpose of modifying the degree of exposureof the mannose when they were incorporated into liposomes.The interaction of glycovesicles with Con A was studied using: (i) agglutination assays; measured bydynamic laser light scattering (DLS); (ii) time resolved fluorescence methods and (iii) surface plasmonresonance (SPR) kinetic measurements. DLS data showed that an increase in hydrophobic chain lengthpromotes a decrease of liposomes hydrodynamic radius. A longer hydrocarbon chain favors a deeperinsertion 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 withthe protein. From SPR measurements the kinetic and equilibrium constants associated to the interactionof ConA with the different glycolipid synthetized were determined.The combination of SPR and fluorescence techniques allowed to study the interaction of Con A withmannosyl glycovesicles at three levels: at the surface, at the interface and deeper into the bilayer.Fondecyt-Chile1120196 1140454 / CONICYT-FONDEQUIP (EQM140112) / SECyT-UNC and Agencia Nacional de Promoción Científica y Tecnológica (ANPCYT) / Conicyt Beca Doctorado Nacional 2112055

Bottom up approaches for amino beta-CD adsorption on gold surfaces. A comparative study

The immobilization of three amino-beta-cyclodextrin derivatives on gold surfaces via different bottom-up approaches was evaluated using cyclic voltammetry and surface plasmon resonance. Direct adsorption on gold and covalent attachment via amide bond formation with carboxylic groups of both the self assembled monolayer of 4-mercapto benzoic acid (4 -MBA) and the electrografted diazonium salt synthesized in situ from 4 -amino benzoic acid (4-ABA) were tested. Amino beta-CD with 1, 2 or 7 amine groups on the primary rim were used. The influence of the immobilization methodologies on the electrochemical properties of the resulting surfaces was studied using hydroquinone and ferricyanide as redox probes. The results indicate that the surface coverage of the molecules as well as their organization at the gold substrate depends on the number of amine groups on the primary rim of 13 -CD. A higher coverage via direct adsorption is obtained using the 7 -amino groups derivative, while the highest coverage is reached with the 2 -amino groups derivative via covalent attachment at diazonium salt electrografted surfaces. A critical discussion about the influence of different strategies used for the immobilization and the number of terminal amine groups on the 13 -CD structure is performed.FONDECYT (Chile) 1151329 CONICET SECyT-UNC Agencia Nacional de Promocion Cientifica y Tecnologica (ANPCYT) (Argentina) Argentina-Chile International Collaboration Grant CONICYT/MINCYT PCCI130050 CH/13/0

Electrooxidation of DNA at glassy carbon electrodes modified with multiwall carbon nanotubes dispersed in polyethylenimine

This work reports the electrochemical response of the complex between dsDNA and PEI formed in solution and at the surface of glassy carbon electrodes (GCE) modified with a dispersion of multi-walled carbon nanotubes in polyethylenimine (CNT-PEI). Scanning Electron Microscopy and Scanning Electrochemical Microscopy demonstrate that the dispersion covers the whole surface of the electrode although there are areas with higher density of CNT and, consequently, with higher electrochemical reactivity. The adsorption of DNA at GCE/CNT-PEI is fast and it is mainly driven by electrostatic forces. A clear oxidation signal is obtained either for dsDNA or a heterooligonucleotide of 21 bases (oligoY) at potentials smaller than those for the oxidation at bare GCE. The comparison of the behavior of DNA before and after thermal treatment demonstrated that the electrochemical response highly depends on the 3D structure of the nucleic acid. © 2011 Elsevier Ltd. All rights reserved

Effect of the Dispersing Agent on the Electrochemical Response of Glassy Carbon Electrodes Modified with Dispersions of Carbon Nanotubes

The electrochemical response of a glassy carbon electrode modified with carbon nanotubes (CNT) dispersed in two solvents, water and DMF, and two polymers, chitosan and Nafion is reported. The films were homogeneous when the dispersing agent was water or DMF. In the case of polymers, the surfaces present areas with different density of CNTs. A more sensitive electrochemical response was obtained when CNTs are dispersed in the solvents. In the case of CNT dispersed with polymers, the nature of the polymer demonstrated to be a critical parameter not only for dispersing the nanotubes but also for the electrochemical activity of the resulting electrodes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Comportamiento electroquímico de moléculas de interés biológico y ambiental: Electroanalítica

El proyecto abarca diferentes aspectos relacionados con la electroquímica de moléculas orgánicas, priorizando las de interés biológico. Se estudia el comportamiento electroquímico de los sistemas enzimáticos, de los macrociclos y sus complejos de inclusión y de las interfases líquido/líquido modificadas o no por monocapas de sustancias anfipáticas, frente al transporte de iones, iones complejos e ionóforos. Se estudian además procesos de adsorción de iones complejos aplicables al análisis de trazas de iones metálicos. En todos los casos se estudian aspectos básicos y sus aplicaciones electroanalíticas. 1) Comportamiento electroquímico de moléculas orgánicas y de sus complejos de inclusión con ciclodextrinas: se estudia el efecto del macrociclo sobre la reacción de transferencia de carga del ácido ascórbico y de otras moléculas de estructura fenólica o derivados de los catecoles, tales como neurotransmisores y sus metabolitos relacionados. 2) Electrodos enzimáticos: se estudia el comportamiento de polifenol oxidasas provenientes de diversas fuentes, frente a sustratos fenólicos o derivados de catecoles, tales como neurotransmisores y sus metabolitos relacionados. Las enzimas se inmovilizan sobre electrodos de carbono y sobre electrodos de sales orgánicas conductoras mediante diferentes metodologías. Se analizan las aplicaciones analíticas. 3) Interfases líquidas: se continúa con el estudio de la transferencia de iones a través de la interfase H2O/1,2-dicloroetano modificada por la presencia de una monocapa de fosfolípido, como así también del mecanismo de transporte de cationes alcalinos y alcalino-térreos en presencia de distintos ligandos. 4) Estudio de la adsorción de complejos de cationes metálicos sobre electrodos de mercurio y de carbono. Se determinan parámetros de la etapa de transferencia de masa y de la adsorción propiamente dicha, tendientes a establecer los mecanismos de reacciones involucradas en las técnicas voltamétricas de adsorción-desorción. Se compara con técnicas voltamétricas de deposición disolución para los mismos cationes metálicos, con especial énfasis en las aplicaciones analíticas relacionadas con la determinación de cationes metálicos a nivel de trazas