Study of biomolecules adsorption on carbon nanotubes for their application as biosensors

Carbon Nanotubes (CNTs) are a new material with electric, mechanical and electrochemical properties that make them interesting for different applications. Due to their high superficial area, the CNTs are very sensitive to molecules adsorbing on them. This property makes them a very good candidate for integrating into biosensors. In this context, the control of the non specific adsorption of molecules different from the one wanting to detect, is a parameter to be known and controlled. Along this Master Final Project, the adsorption of streptavidin, a biomolecule widely used in biomedical research, on the surface of Single Walled NanoTubes (SWNTs) have been studied. The highly specific biotin-streptavidin system have been used for specifically binding the streptavidin to the surface of the nanotube and to control the degree of specific / non specific adsorption. SWNTs with different functional groups at the surface have been considered. The horseradish peroxidase (HRP)-catalyzed oxidation of 3,3’-5,5’-tetramethylbenzidine (TMB) have been used as colorimetric test to determine the presence of streptavidin onto the SWNTs. The non specific adsorption of the protein has been intended to be prevented. Among the great variety of surfactants and molecules used to prevent the adsorption, polyethylene glycol (PEG), Tween20® and Pluronic® F-127 have been used. No complete blockage have been achieved. Once the adsorption of that protein over the surface of SWNTs has been known, it has been used to detect DNA hybridization, binding on strand to the nanotube in a specific way. The detection of the hybridization have been carried out optically by a fluorescent probe on the complementary strand

Purification of surface-modified arc-discharge single-walled carbon nanotubes by centrifugation processes

Talk delivered at GDR-I GNT2013 conference, held at Guidel-Plages (France), from 8th-12th April 2013.Arc-discharge single-walled carbon nanotubes (SWCNTs) demonstrate well-defined spectroscopic responses and a high structural quality. In addition, the arc-discharge technique allows the synthesis of relatively large amounts of material, and the product is available at moderate prices. However, pristine arc-discharge SWCNTs contain large amounts of impurities, including catalyst metals, graphitic particles, and amorphous carbon. Well-purified commercial samples are expensive since current purification processes are time consuming and have low yields. Liquid media, which are necessary for the purification, change the physical aggregation of the SWCNTs or modify its chemical reactivity. Therefore, chemical studies on high-purity arc-discharge SWCNTs are limited. In this communication, we present our results on SWCNT purification by centrifugation or ultracentrifugation in aqueous media. More specifically, we study the influence of surface chemistry on the separation of arc-discharge SWCNTs from their impurities during the centrifugation. The results of processing chemically modified materials are analyzed in terms of graphitic and amorphous carbon impurities, residual metal content, and SWCNT spectral characteristics.Peer reviewe

Hydrothermal synthesis of 1D TiO2 nanostructures for dye sensitized solar cells

El pdf del artículo es la versión pre-print.Mono-dimensional titanium oxide nanostructures (multi-walled nanotubes and nanorods) were synthesized by the hydrothermal method and applied to the construction of dye sensitized solar cells (DSCs). First, nanotubes (TiNTs) and nanotubes loaded with titanium oxide nanoparticles (TiNT/NPs) were synthesized with specific surface areas of 253 m2/g and 304 m2/g, respectively. After that, thermal treatment of the nanotubes at 500 °C resulted in their transformation into the corresponding anatase nanorods (TiNT-Δ and TiNT/NPs-Δ samples). X-ray diffraction and Raman spectroscopy data indicated that titanium oxide in the pristine TiNT and TiNT/NP samples was converted into anatase phase TiO2 during the heating. Additionally, specific surface areas and water adsorption capacities decreased after the heat treatment due to the sample agglomeration and the collapse of the inner nanotube channels. DSCs were fabricated with the nanotube TiNT and TiNT/NP samples and with the anatase nanorod TiNT-Δ and TiNT/NPs-Δ samples as well. The highest power conversion efficiency of η = 3.12% was obtained for the TiNT sample, despite its lower specific surface compared with the corresponding nanoparticle-loaded sample (TiNT/NP). © 2011 Elsevier B.V. All rights reserved.This work was funded by the Government of Aragon and La Caixa (project ref. GA-LC-041/2008) and by the Spanish MICINN (projects ref. EUI2008-00152 and ENE2008-04373). We thank the Spanish National Research Council (CSIC) for the JAE-Doc contracts awarded to Y.Y. and A.A. To the Xarxa de Referència en Materials Avanc¸ ats per a l’Energia, XaRMAE (Reference Center for Advanced Materials for Energy) of the Catalonia Government.Peer Reviewe

Preparación y caracterización de quantum dots de grafeno (GQDs) a partir de grafito

En este proyecto se presenta el estudio de un método para la obtención de quantum dots de grafeno (GQDs) a partir de polvo de grafito, aplicando para ello el método de Hummers con algunas modificaciones. Para facilitar la aplicación de grafeno en nanodispositivos y para modular eficientemente el intervalo de banda, una estrategia prometedora es convertir las hojas de grafeno bidimensionales en puntos cuánticos cero-dimensionales, (GQDs del inglés Graphene quantum dots). Los GQDS son puntos cuánticos de grafeno cero-dimensionales. Estudios teóricos y experimentales han indicado que además de sus propiedades de transporte únicas, el confinamiento cuántico y el efecto frontera podrían resultar en fenómenos y propiedades de alto interés. se han estudiado distintas condiciones de producción y operación y se han caracterizado los GQDs mediante técnicas de microscopia, difracción de rayos X y diversas técnicas espectroscópicas

Electrochemical behavior of hybrid carbon nanomaterials: the chemistry behind electrochemistry

The unzipping of temperature-induced multi-walled carbon nanotubes (MWCNTs) to yield graphene nanoribbons (GNRs) has been studied. These carbon nanomaterials consisting of MWCNTs and unzipped MWCNTs have been synthesized, thoroughly characterized, and subsequently evaluated for electrochemical sensing. Three temperatures (55, 65 and 75 ºC) yielding three carbon nanomaterial termed as GNR-55, GNR-65 and GNR-75, respectively, were carefully studied. Interestingly, GNR-65 became the most suitable material for the electrochemical sensing of a wide range of model analytes displaying the best electrochemical response with independence of the analysed molecule. This electrochemical behaviour seems to be associated to the progress of the unzipping reaction that influences the balance between the Csp2/Csp3 ratio, the graphitic fraction and the type of functional groups introduced. These results revealed the importance of the temperature in the synthesis process, for tailoring carbon nanomaterials which could be used in a particular molecular detection application opening new opportunities for electrochemical sensing applications.This work has been Financial supported by the Spanish Ministry of Science and Innovation (CTQ2011-28135), the NANOAVANSENS program from the Community of Madrid (S2013/MIT-3029), the Spanish MINECO (ENE2013-48816-C5-5-R), the Government Aragon (Project DGA_ESF-T66 CNN) and the European Social Fund (ESF). D. A. M. acknowledges the FPU fellowship from the Ministry of Education, Culture and Sports. D. M. M.-G. acknowledges the fellowship received from the NANOAVANSENS program.Peer reviewe

In-vitro toxicity of carbon nanotube/polylysine colloids to colon cancer cells

Single-walled carbon nanotubes (SWCNTs) are thoroughly purified and dispersed in an aqueous solution of high molecular weight poly-L-lysine (pLlys). Human intestinal epithelial Caco-2/TC7 cells are incubated with the SWCNT dispersions in pLlys, and their effects on cell viability are studied by image flow cytometry. No significant changes are observed in the cell culture wells up to pLlys concentrations of 10 g mL-1. However, high mortality is detected at pLlys concentrations of 100 g mL-1. The presence of oxygen-free SWCNTs does not modify the effects of pLlys on cell cultures at any of the tested concentrations (£ 1 g mL-1). In addition, SWCNTs having an 8 wt.% of surface oxygen are tested with identical results. Thus, purified SWCNTs, even bearing oxygen functional groups, act as inert particles in the cell culture medium. This result supports the applicability of SWCNTs as carriers in pharmacological formulations against digestive tract diseases.This work was funded by the Spanish Ministry MINECO and the European Regional Development Fund under the projects PRI-PIBAR-2011-1 and ENE2013-48816-C5-5-R, and the Government of Aragon and the European Social Fund (DGA-ESF-T66 Grupo Consolidado and DGA-ESF-B61 Grupo Consolidado).Peer reviewe

Epoxy composites with covalently anchored amino-functionalized SWNTs: Towards the tailoring of physical properties through targeted functionalization

First published on the web August 24th, 2011Functionalization of single-walled carbon nanotubes (SWNTs) with covalently grafted amine moieties provides reactive fillers with potential for covalent anchoring to an epoxy matrix. Manufacturing and characterization of a high performance epoxy system reinforced with as-grown and aminated SWNTs are presented through four different approaches. Epoxy composite materials incorporating SWNTs aminated through sidewall addition reactions present enhanced mechanical, thermal and electrical properties, beyond the effect of unfunctionalized SWNTs. The functionalization pathways studied here lead to a composite with specific improvements in some of the physical properties of the epoxy matrix, which enables the tailored design of the composite's properties through functionalization. The amination via diazonium reaction with 4-aminobenzylamine is especially effective in enhancing the tensile and impact properties of the epoxy composites (44% improvement in impact strength at 0.1 wt% loading) and leads to the highest increase in elastic modulus reported so far for the integration of aminated nanotubes into epoxy resin. Composites incorporating aminated SWNTs throughout the 1,3-dipolar cycloaddition reaction stand out for their thermo-oxidative stability and thermomechanical properties. The incorporation of as-produced arc-discharge SWNTs into the TGAP/DDS epoxy matrix leads to composite materials with the highest electrical conductivity among all the studied samples. This journal is © The Royal Society of Chemistry.The present work was carried out with financial support from the NRC-CSIC collaboration project and fellowships from MICINN Spanish Ministry (FPU grant) and CAI-DGA and Europa XXI programmes. J.M.G.D. would like to thank Dr Benoit Simard and Dr Yadienka Martinez of SIMS-NRC for their close collaboration. Special thanks go to Prof. Maurizio Prato for kindly allowing a short research stay in his group, and his entire team. Epoxy reagents were received as a gift from Huntsman, which is gratefully acknowledged.Peer Reviewe

Epoxy composites with covalently anchored amino-functionalized SWNTs: Towards the tailoring of physical properties through targeted functionalization

Functionalization of single-walled carbon nanotubes (SWNTs) with covalently grafted amine moieties provides reactive fillers with potential for covalent anchoring to an epoxy matrix. Manufacturing and characterization of a high performance epoxy system reinforced with as-grown and aminated SWNTs are presented through four different approaches. Epoxy composite materials incorporating SWNTs aminated through sidewall addition reactions present enhanced mechanical, thermal and electrical properties, beyond the effect of unfunctionalized SWNTs. The functionalization pathways studied here lead to a composite with specific improvements in some of the physical properties of the epoxy matrix, which enables the tailored design of the composite's properties through functionalization. The amination via diazonium reaction with 4-aminobenzylamine is especially effective in enhancing the tensile and impact properties of the epoxy composites (44% improvement in impact strength at 0.1 wt% loading) and leads to the highest increase in elastic modulus reported so far for the integration of aminated nanotubes into epoxy resin. Composites incorporating aminated SWNTs throughout the 1,3-dipolar cycloaddition reaction stand out for their thermo-oxidative stability and thermomechanical properties. The incorporation of as-produced arc-discharge SWNTs into the TGAP/DDS epoxy matrix leads to composite materials with the highest electrical conductivity among all the studied samples. This journal is © The Royal Society of Chemistry.The present work was carried out with financial support from the NRC-CSIC collaboration project and fellowships from MICINN Spanish Ministry (FPU grant) and CAI-DGA and Europa XXI programmes. J.M.G.D. would like to thank Dr Benoit Simard and Dr Yadienka Martinez of SIMS-NRC for their close collaboration. Special thanks go to Prof. Maurizio Prato for kindly allowing a short research stay in his group, and his entire team. Epoxy reagents were received as a gift from Huntsman, which is gratefully acknowledged.Peer Reviewe

Carbon nanotube networks as gas sensors for NO2 detection

Networks of different carbon nanotube (CNT) materials were investigated as resistive gas sensors for NO2 detection. Sensor films were fabricated by airbrushing dispersions of double-walled and multi-walled CNTs (DWNTs and MWNTs, respectively) on alumina substrates. Sensors were characterized by resistance measurements from 25 to 250 °C in air atmosphere in order to find the optimum detection temperature. Our results indicate that CNT networks were sensitive to NO2 concentrations as low as 0.1 ppm. All tested sensors provided significantly lower response to interfering gases such as H2, NH3, toluene and octane. We demonstrate that the measured sensitivity upon exposure to NO2 strongly depends on the employed CNT material. The highest sensitivity values were obtained at temperatures ranging between 100 and 200 °C. The best sensor performance, in terms of recovery time, was however achieved at 250 °C. Issues related to the gas detection mechanisms, as well as to CNT network thermal stability in detection experiments performed in air at high operation temperatures are also discussed.This work has been supported by MEC (Spain, projects TEC2004-05098-C02-01/MIC and TEC2004-05098-C02-02/MIC, Programa I3 2006 8 0I 060) and the European Regional Development Fund (ERDF).Peer reviewe

Novel selective sensors based on carbon nanotube films for hydrogen detection

Novel resistive gas sensors based on single-walled carbon nanotubes (SWNTs) as an active sensing element have been evaluated for hydrogen detection. Sensor films were fabricated by airbrushing SWNT dispersions on alumina substrates. The employed SWNT materials were either chemically functionalized with Pd or sputtered with Pd to enhance their sensitivity to hydrogen. Sensors were characterized by dc electrical measurements in nitrogen and air atmosphere. The response to hydrogen and the cross sensitivity to gases such as ammonia, toluene and octane were studied. Aged Pd-functionalized SWNT films exhibited good sensitivity and selectivity to hydrogen at room temperature. The effect of aging, thermal treatments and the employed carrier gas were also investigated.This work is been supported by MEC (Spain, Projects TEC2004-05098-C02-01/MIC and TEC2004-05098-C02-02/MIC). The authors wish to thank Christine Würzburger of Heraeus S.A. for kindly providing the Heraeus MSP 769 substrates.Peer reviewe