Ernest Mendoza

Polytechnic University of Catalonia, Barcino, Catalonia, Spain

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Publications (43)215.47 Total impact

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    ABSTRACT: Show me the way: protein building blocks are programmed to assemble hierarchically and yield a defined fiber morphology of micrometric length and precise nanometric diameter. The key step of this method is to align the building blocks with an AC field prior to assembly. The resulting protein nanofibers are straightforwardly integrated with the circuitry for potential applications in bionanotechnology.
    Small 06/2014; · 7.82 Impact Factor
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    ABSTRACT: The catalytic activity of gold depends on particle size, with the reactivity increasing as the particle diameter decreases. However, investigations into behaviour in the subnanometre regime (where gold exists as small clusters of a few atoms) began only recently with advances in synthesis and characterization techniques. Here we report an easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O2. We show that single gold atoms are not active, but they aggregate under reaction conditions into gold clusters of low atomicity that exhibit a catalytic activity comparable to that of sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero. Theoretical calculations show that gold clusters are able to activate thiophenol and O2 simultaneously, and larger nanoparticles are passivated by strongly adsorbed thiolates. The combination of both reactants activation and facile product desorption makes gold clusters excellent catalysts.
    Nature Chemistry 09/2013; 5(9):775-81. · 21.76 Impact Factor
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    ABSTRACT: We report the straightforward oriented covalent attachment of antibodies (Abs) on the surface of carboxylated multiwalled carbon nanotube-polystyrene (MWCNT-PS) materials. The combination of this composite material, applied as a robust electrochemical transducer platform, and its covalent functionalization with Abs in a controlled way by means of a two-step process, could contribute to the development of highly sensitive immunosensor devices. Using the simple and versatile carbodiimide chemistry, Abs were attached to the carboxylic groups of the MWCNT-PS composite surfaces via their superficial amine groups. By taking into account the Ab isoelectric point and the net charge of the composite surface, we engineered an immobilization process to achieve the oriented binding of the Ab molecules by favoring an ionic pre-adsorption step before covalent binding occurred. Thus, the antigen binding capacity of the attached Abs was enhanced by up to 10 times with respect to the capacity estimated for a random spatial distribution of these molecules. The proposed strategy would also serve as a model for the efficient biofunctionalization of other carboxylated carbon-based polymer composite materials with potential applications in the biosensor field.
    Biosensors & bioelectronics 12/2012; 43C:274-280. · 5.43 Impact Factor
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    ABSTRACT: We report the straightforward oriented covalent attachment of antibodies (Abs) on the surface of carboxylated multiwalled carbon nanotube-polystyrene (MWCNT-PS) materials. The combination of this composite material, applied as a robust electrochemical transducer platform, and its covalent functionalization with Abs in a controlled way by means of a two-step process, could contribute to the development of highly sensitive immunosensor devices. Using the simple and versatile carbodiimide chemistry, Abs were attached to the carboxylic groups of the MWCNT-PS composite surfaces via their superficial amine groups. By taking into account the Ab isoelectric point and the net charge of the composite surface, we engineered an immobilization process to achieve the oriented binding of the Ab molecules by favoring an ionic pre-adsorption step before covalent binding occurred. Thus, the antigen binding capacity of the attached Abs was enhanced by up to 10 times with respect to the capacity estimated for a random spatial distribution of these molecules. The proposed strategy would also serve as a model for the efficient biofunctionalization of other carboxylated carbon-based polymer composite materials with potential applications in the biosensor field.
    Biosensors and Bioelectronics 01/2012; · 5.44 Impact Factor
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    ABSTRACT: This work reports on the fabrication and performance of a simple amperometric immunosensor device to be potentially used for the detection of serum anti-citrullinated peptide antibodies (ACPAs), which are specific for rheumatoid arthritis (RA) autoimmune disease. Sera of RA patients contain antibodies to different citrullinated peptides and proteins such as fibrin or filaggrin. Herein, a chimeric fibrin-filaggrin synthetic peptide (CFFCP1) was used as a recognition element anchored to the surface of a multiwalled carbon nanotube-polystyrene (MWCNT-PS) based electrochemical transducer. The transducer fabrication process is described in detail together with its successful electrochemical performance in terms of repeatability and reproducibility of the corresponding amperometric response. The resulting immunosensor approach was initially tested in sera of rabbits previously inoculated with the synthetic peptide and eventually applied to the detection of ACPAs in human sera. A comparative study was carried out using control serum from a blood donor, which demonstrated the selectivity of the immunosensor response and its sensitivity for the detection of anti-CFFCP1 antibodies present in RA patients.
    Biosensors & bioelectronics 09/2011; 27(1):113-8. · 5.43 Impact Factor
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    ABSTRACT: Small gold nanoclusters in a very narrow size distribution (1.1 ± 0.5 nm) have been stabilized onto multiwalled carbon nanotubes (MWCNT). Theoretical studies supported by XPS and (16)O(2)/(18)O(2) isotopic exchange experiments have shown that, on small gold nanoparticles (0.9-1.5 nm), dissociation of molecular O(2) and formation of a surface oxide-like layer is energetically favorable and occurs at room temperature, while O(2) recombination and desorption involves a larger activation barrier. CO titration experiments and theoretical studies demonstrate that the reactivity of the oxidized particles toward CO does not only depend on particle size but also on oxygen coverage. The oxidation-reduction process described is reversible, and the oxidized nanoparticles are active in the epoxidation of styrene with air.
    Journal of the American Chemical Society 06/2011; 133(26):10251-61. · 10.68 Impact Factor
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    ABSTRACT: A series of 2.5% Rh/M@Al2O3 model catalysts were prepared by supporting Rh on high-area γ-Al2O3, resulting in a surface covered by a monolayer (4.5–7 atoms/nm2) of MOx promoter oxides (M=Fe, V, Nb, Ta, Ti, Y, Pr, Nd, Sm). The catalysts were extensively characterized and evaluated for the conversion of synthesis gas to oxygenates at 553K, 5.0MPa, H2/CO=1, and space velocity adjusted to attain CO conversion around 15%. The broad range of products formed depending on the specific promoter were, for the first time, quantitatively described using the selectivity parameter (Φ) defined here, which indicates, for a given reaction product, the contribution of carbon atoms derived from dissociative (Cdis) and nondissociative (Cins) activation of CO. Both the catalytic activity and, more interestingly, the selectivity pattern given by the Φ parameter were correlated with the electronic properties of the MOx promoters (i.e., electron-donating/electron-withdrawing capacity) for an extensive series of catalysts. Low-temperature and at-work CO-FTIR experiments suggested that the high activity and hydrocarbon selectivity displayed by catalysts promoted by more electron-withdrawing (acidic) oxide promoters (e.g., TaOx) were related to a higher proportion of bridged Rh2(CO)B adsorption sites and to a higher electron density (i.e., a higher electron back-donation ability) of the Rh0 surface sites, both factors promoting CO dissociation events. In contrast, linear CO adsorption on Rh0 sites displaying decreased electron back-donation in catalysts promoted by electron-donating (basic) oxides (e.g., PrOx, SmOx) was likely related to nondissociative CO activation and thus to the selective formation of oxygenates. TEM, XPS, and CO-FTIR results pointed to differences in morphology, rather than size or partial electronic charge, of the nanosized Rh0 crystallites as the likely cause for the different proportions of CO adsorption sites. The Rh0 NP morphology, both as-reduced and at-work, is a function of the electronic properties of the underlying promoter oxide.
    Journal of Catalysis - J CATAL. 01/2011; 280(2):274-288.
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    Small 08/2010; 6(16):1753-6. · 7.82 Impact Factor
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    ABSTRACT: Carbon nanotube-polymer composites have shown to be suitable materials for the fabrication of electrochemical transducers. The exposed surface of these materials is commonly passivated by a very thin layer of the polymer component that buries the conductive carbon particles. Working with multi-walled carbon nanotube-polystyrene (MWCNT-PS) composite structures, it was previously described how a simple low power oxygen plasma process produced an effective etching of the composite surface, thereby exposing the conductive surface of CNTs. This work shows how this plasma process not only gave rise to a suitable composite conductive surface for electrochemical sensing but simultaneously exposed and created a high density of oxygen-containing functional groups at both the CNT and the PS components, without affecting the material's mechanical stability. These chemical groups could be effectively modified for the stable immobilization of biological receptors. A detailed chemical characterization of the plasma-activated composite surface was possible using x-ray photoelectron spectroscopy. The material reactivity towards the tethering of a protein was studied and protein-protein interactions were then evaluated on the modified composite transducers by scanning electron microscopy. Finally, an amperometric immunosensor approach for the detection of rabbit Immunoglobulin G target analyte was described and a minimum concentration of 3 ng ml(-1) was easily measured.
    Nanotechnology 09/2009; 20(33):335501. · 3.84 Impact Factor
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    ABSTRACT: We report an alternative method combining dielectrophoresis and impedance spectroscopy to provide rapid, accurate measurement of dielectrophoretic collection of single-walled carbon nanotubes (SWNTs) in real time. We analyzed a Triton X-100 suspension of mixed SWNTs to measure their precise dielectrophoretic collection behavior. Results indicate that our sample contains 21.5% of metallic and 78.5% of semiconducting carbon nanotubes before separation, and that the range of 1-15 MHz is ideal to collect only the metallic ones. Optical absorption was used to confirm these proportions. We discuss the possible errors associated with using purely a Raman technique to validate the type of SWNTs collected in suspension.
    Applied Physics Letters 03/2009; 88:243109. · 3.79 Impact Factor
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    ABSTRACT: The purity of the multi-wall carbon nanotubes (MWCNTs) from catalyst nanoparticles (cobalt and iron) after conventional nitric acid refluxing has been assessed by standard methods and magnetic measurements. X-ray diffraction and energy dispersive X-ray spec-troscopy analyses are not suitable since the catalyst amounts quickly become beyond the detection limit of such techniques. Inductively coupled plasma spectroscopy is useful for this purpose, however it requires a large amount of sample and a long sample processing time since the MWCNTs must be completely destroyed. By contrast, magnetic measure-ments are a fast and nondestructive method to monitor the catalyst content, showing the existence of a small but detectable signal even for the purest sample, still far from its detection limit. Hence, magnetic measurements are extremely sensitive to detect cata-lyst impurities and can be used as a quick, first order, tool to evaluate the level of magnetic impurities.
    Carbon. 12/2008; 47(3).
  • Angewandte Chemie International Edition 12/2008; 47(50):9752-5. · 11.34 Impact Factor
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    ABSTRACT: Studies regarding the environmental impact of engineered nanoparticles (ENPs) are hampered by the lack of tools to localize and quantify ENPs in water, sediments, soils, and organisms. Neutron activation of mineral ENPs offers the possibility of labeling ENPs in a way that avoids surface modification and permits both localization and quantification within a matrix or an organism. Time-course experiments in vivo also may be conducted with small organisms to study metabolism and exposure, two aspects currently lacking in ecotoxicological knowledge about ENPs. The present report explains some of the prerequisites and advantages of neutron activation as a tool for studying ENPs in environmental samples and ecologically relevant organisms, and it demonstrates the suitability of neutron activation for Ag, Co/Co3O4, and CeO2 nanoparticles. In a preliminary experiment with the earthworm Eisenia fetida, the dietary uptake and excretion of a Co nanopowder (average particle size, 4 nm; surface area, 59 m2/g) were studied. Cobalt ENPs were taken up to a high extent during 7 d of exposure (concentration ratios of 0.16-0.20 relative to the ENP concentration in horse manure) and were largely retained within the worms for a period of eight weeks, with less than 20% of absorbed ENPs being excreted. Following dissection of the worms, 60Co was detected in spermatogenic cells, cocoons, and blood using scintillation counting and autoradiography. The experimental opportunities that neutron activation of ENPs offer are discussed.
    Environmental Toxicology and Chemistry 10/2008; 27(9):1883-7. · 2.62 Impact Factor
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    ABSTRACT: Purification and shortening of single-walled carbon nanotubes (SWNTs) is carried out by treatment with steam. During the steam purification the graphitic shells coating the catalytic metal particles are removed. Consequently, the exposed catalytic particles can be easily dissolved by treatment with hydrochloric acid. No damage to the carbon nanotube tubular structure is observed, even after prolonged treatment with steam. Samples are characterized by HRTEM, TGA, magnetic measurements, Raman spectroscopy, AFM, and XPS.
    Small 10/2008; 4(9):1501-6. · 7.82 Impact Factor
  • Small 08/2008; 4(8):1076-9. · 7.82 Impact Factor
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    Analytica Chimica Acta. 03/2008; 611(2):250.
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    ABSTRACT: We report a novel electrode material for the detection of human bio-potentials using carbon nanofibre ( CNF) arrays functionalized with silver/silver chloride ( Ag-AgCl) core-shell nanoparticles. The CNFs are protected against detachment using a thin polymer film, which firmly secures the fibres to the substrate surface. The core-shell Ag-AgCl nanoparticles on the CNF surfaces clearly enhance transduction in ionic media as shown by cyclic voltammetry and impedance spectroscopy. We infer that these functionalized CNF arrays can be utilized as dry electrophysiological sensors for bio-potential monitoring applications.
    Nanotechnology 03/2008; 18. · 3.84 Impact Factor
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    ABSTRACT: In this work we present the fabrication and characterization of immunosensors based on polystyrene (PS)-multiwalled carbon nanotube (MWCNT) composites. The electrochemical properties of the sensors have been investigated and show that the surface area is increased upon addition of the MWCNT-PS layer. Furthermore, a plasma activation process is used to partially remove the PS and expose the MWCNTs. This results in a huge increase in the electrochemical area and opens up the possibility of binding biomolecules to the MWCNT wall. The MWCNTs have been functionalized covalently with a model antibody (rabbit IgG). The biosensors have been tested using amperometric techniques and show detection limits comparable to standard techniques such as ELISA.
    Nanotechnology 02/2008; 19(7):075102. · 3.84 Impact Factor
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    ABSTRACT: This work reports on the development of a graphite-polystyrene composite electrode of planar configuration, containing silver(II) oxide and copper(II) oxide catalysts (AgO-CuO), for the measurement of electrochemical oxygen demand (EOD). Optimisation studies of the composite composition as well as conditions for its processing on planar substrates and generation of an appropriate electrochemical active area resulted in the scalable fabrication of robust composite electrodes. These were evaluated with glucose as target analyte. They showed competitive low limits of detection in a linear concentration range from 5 mgL(-1) to 1400 mgL(-1) of O(2). Besides, they were stable for at least one year. The determination of EOD in wastewater samples coming from production lines of parenteral food and winemaking was successfully carried out.
    Analytica chimica acta 02/2008; 607(2):176-82. · 4.31 Impact Factor
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    ABSTRACT: This work reports on the quantitative determination of the carboxylic groups created upon HNO3 treatment at multi-wall carbon nanotube (MWCNT) surface. To this purpose, MWCNTs have been oxidized by refluxing in acid for different periods of time (from 1h to 12h). The main goal of the present study comprises the development of a simple analytical methodology based on Boehm’s titration that enables the rapid estimation of the total carboxylic groups and their discrimination from the total oxidized sites created at MWCNT surface as a result of the acid treatment. The trends observed are correlated with Raman spectroscopy analyses.
    Chemical Physics Letters 01/2008; 462:256-259. · 2.15 Impact Factor

Publication Stats

343 Citations
215.47 Total Impact Points

Institutions

  • 2011–2014
    • Polytechnic University of Catalonia
      • CRNE - Centre for Research in Nanoengineering
      Barcino, Catalonia, Spain
    • Barcelona Microelectronics Institute
      Barcino, Catalonia, Spain
  • 2009
    • Spanish National Research Council
      • Instituto de Microelectrónica de Barcelona
      Madrid, Madrid, Spain
  • 1998–2009
    • University of Surrey
      • • Advanced Technology Institute (ATI)
      • • Department of Electronic Engineering
      Guildford, ENG, United Kingdom
  • 2008
    • Catalan Institute of Nanoscience and Nanotechnology
      Barcino, Catalonia, Spain
    • Catalan Institution for Research and Advanced Studies
      Barcino, Catalonia, Spain
  • 2005
    • University of Nottingham
      • Department of Mechanical, Materials and Manufacturing Engineering
      Nottingham, ENG, United Kingdom