Leonardo G. Paterno

University of Brasília, Brasília, Federal District, Brazil

Are you Leonardo G. Paterno?

Claim your profile

Publications (41)34.81 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Bionanocomposite films have been prepared by casting an aqueous suspension of acetylated starch (ST) and poly(vinyl alcohol) (PVA) loaded with graphene oxide (GO). A photochemical and reagentless method has been successfully performed to convert the GO phase into reduced graphene oxide (RGO). The nanocomposites have displayed improved thermal and electrical properties when the amount of the GO phase is increased and properly converted to RGO. The molecular-level interactions between components are mainly hydrogen-bonding type according to attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and Raman spectroscopies, as well as thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has confirmed the effective mixing between the GO and the ST-PVA matrix. The thermal diffusivity and electrical resistivity of ST-GO nanocomposites have increased one order and decreased two orders of magnitude, respectively, after the photochemical treatment. These findings have confirmed the effectiveness of the proposed approach to produce starch-based nanocomposites with improved thermal and electrical properties.
    Carbohydrate polymers. 06/2014; 106:305-11.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Conjugated polymers are organic materials endowed with a π-electron conjugation along the polymer backbone that present appealing electrical and optical properties for technological applications. By using conjugated polymeric materials in the nanoscale, such properties can be further enhanced. In addition, the use of nanostructured materials makes possible miniaturize devices at the micro/nano scale. The applications of conjugated nanostructured polymers include sensors, actuators, flexible displays, discrete electronic devices, and smart fabric, to name a few. In particular, the use of conjugated polymers in chemical and biological sensors is made feasible owning to their sensitivity to the physicochemical conditions of its surrounding environment, such as chemical composition, pH, dielectric constant, humidity or even temperature. Subtle changes in these conditions bring about variations on the electrical (resistivity and capacitance), optical (absorptivity, luminescence, etc.), and mechanical properties of the conjugated polymer, which can be precisely measured by different experimental methods and ultimately associated with a specific analyte and its concentration. The present review article highlights the main features of conjugated polymers that make them suitable for chemical sensors. An especial emphasis is given to nanostructured sensors systems, which present high sensitivity and selectivity, and find application in beverage and food quality control, pharmaceutical industries, medical diagnosis, environmental monitoring, and homeland security, and other applications as discussed throughout this review.
    Journal of Nanoscience and Nanotechnology 01/2014; 14(9). · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Iron oxide nanostructured (ION) electrodes were assembled layer-by-layer onto ITO-coated glass substrates and their structure, morphology, and electrochemical properties were investigated, the latter aiming at the development of a chemical sensor for Cu2+. The electrodes were built by immersing the substrate alternately into an aqueous colloidal suspension of positively charged magnetite nanoparticles (np-Fe3O4, 8 nm) and an aqueous solution of anionic sodium sulfonated polystyrene (PSS). The adsorbed amount of both materials was monitored ex-situ by UV-vis spectroscopy and it was found to increase linearly with the number of deposition cycles. The resulting films feature a densely-packed structure of magnetite nanoparticles, as suggested by AFM and Raman spectroscopy, respectively. Cyclic voltammograms of electrodes immersed in acetate buffer (pH 4.6) displayed three electrochemical events that were tentatively ascribed to the reduction of Fe(III) oxy-hydroxide to magnetite, reduction of maghemite to magnetite, and finally oxidation of magnetite to maghemite. The effect of np-Fe3O4/PSS bilayers on the ION electrode performance was to increase the anodic and cathodic currents produced during electrochemical oxidation-reduction of the Fe(CN)3−/4− redox couple. With more bilayers, the ION electrode provided higher anodic/cathodic currents. Moreover, the redox couple exhibited a quasi-reversible behavior at the ION electrode as already observed with other working electrode systems. Fitting of voltammetry data provided the apparent electron transfer constants, which were found to be higher in ION electrodes for both redox couples (Fe(CN)3−/4− and Cu2+/0). By means of differential pulsed anodic stripping voltammetry, the ION electrodes were found to respond linearly to the presence of Cu2+ in aqueous samples in the range between 1.0 and 8.0×10−6 mol·L−1 and displayed a limit of detection of 0.3×10−8 mol·L−1. The sensitivity was ∼0.6 μA/μmol·L−1. In standard addition and recovery experiments performed with tap water the recovery was about 102%–119%. In similar experiments conducted with ground and instant coffee samples the recovery was 92.5% and 103%, respectively. Furthermore, the ION electrodes were almost insensitive to the presence of common interfering ions, such as Zn2+, Mn2+, Ni2+, and Fe3+, even at concentrations ten times higher than that of Cu2+.
    Journal of Nanoscience and Nanotechnology 01/2014; 14(9). · 1.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Multilayered nanocomposite films (thickness 50-90 nm) of cobalt ferrite nanoparticles (np-CoFe2O4, 18 nm) were deposited on top of interdigitated microelectrodes by the layer-by-layer technique in order to study their dielectric properties. For that purpose, two different types of nanocomposite films were prepared by assembling np-CoFe2O4 either with poly(3,4-ethylenedioxy thiophene):poly(styrene sulfonic acid) or with polyaniline and sulfonated lignin. Despite the different film architectures, the morphology of both was dominated by densely-packed layers of nanoparticles surrounded by polyelectrolytes. The dominant effect of np-CoFe2O4 was also observed after impedance spectroscopy measurements, which revealed that dielectric behavior of the nanocomposites was largely influenced by the charge transport across nanoparticle-polyelectrolyte interfaces. For example, nanocomposites containing np-CoFe2O4 exhibited a single low-frequency relaxation process, with time constants exceeding 15 ms. At 1 kHz, the dielectric constant and the dissipation factor (tan δ) of these nanocomposites were 15 and 0.15, respectively. These values are substantially inferior to those reported for pressed pellets made exclusively of similar nanoparticles. Impedance data were further fitted with equivalent circuit models from which individual contributions of particle's bulk and interfaces to the charge transport within the nanocomposites could be evaluated. The present study evidences that such nanocomposites display a dielectric behavior dissimilar from that exhibited by their individual counterparts much likely due to enlarged nanoparticle-polyelectrolyte interfaces.
    Physical Chemistry Chemical Physics 10/2013; · 3.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-thin (thicknesses of 50–90 nm) nanocomposite films of cobalt ferrite nanoparticles (np-CoFe 2 O 4 , 18 nm in diameter) and polyelectrolytes (doped polyaniline-PANI, poly-3,4-ethylenedioxy thiophene: polystyrene sul-fonic acid–PEDOT:PSS, and sulfonated lignin-SL) are assembled layer-by-layer onto interdigitated microelec-trodes aiming at to create novel nanostructured sensoactive materials for liquid media chemical sensors. The nanocomposites display a distinctive globular morphology with nanoparticles densely-packed while surrounded by polyelectrolytes. Due to the presence of np-CoFe 2 O 4 the nanocomposites display low electrical conductivity according to impedance data. On the other hand, this apparent shortcoming turns such nanocomposites much more sensitive to the presence of ions in solution than films made exclusively of conducting polyelectrolytes. For example, the electrical resistance of np-CoFe 2 O 4 /PEDOT:PSS and PANI/SL/np-CoFe 2 O 4 /SL architectures has a 10-fold decrease when they are immersed in 20 mmol. L −1 NaCl solution. Impedance spectra fitted with the response of an equivalent circuit model suggest that the interface created between nanoparticles and poly-electrolytes plays a major role on the nanocomposites electrical/dielectrical behavior. Since charge transport is sensitive to nanoparticle-polyelectrolyte interfaces as well as to the physicochemical conditions of the environ-ment, the np-CoFe 2 O 4 -based nanocomposites can be used as sensing elements in chemical sensors operated under ac regime and room temperature.
    Journal of Nanofluids. 09/2013; 2(3):175-183.
  • [Show abstract] [Hide abstract]
    ABSTRACT: ______________________________________________________________________________________________________ Resumo: Os polímeros condutores são polímeros contendo ligações conjugadas em suas cadeias que se tornam condutores através de processos de dopagem. A grande gama de polímeros e a possibilidade do controle de suas propriedades em escala molecular têm tornado tais materiais extremamente atrativos em inúmeras aplicações. Aqui revisaremos os princípios básicos do funcionamento dos sensores e como os polímeros condutores podem ser usados para aumentar e melhorar a sua detecção e/ou seletividade. Na terceira e última etapa cobriremos o uso de polímeros condutores em biossensores. Palavras-chave: Sensores; polímeros condutores; nanotecnologia; aplicações. ___________________________________________________________________________________________________ Abstract: Conducting polymers are polymers containing conjugated bonds in their backbones that can become conductive through several doping processes. A wide range of polymers and the possibility of controlling their properties at the molecular scale have made such materials extremely attractive in numerous applications. Here we review the basic principles of sensors and how conductive polymers can be used to enhance sensor detection limit and/or selectivity. In the third and final part, we will review the use of conducting polymers in biosensors.
    remap. 01/2013;
  • Leonardo G. Paterno, Maria A. G. Soler
    [Show abstract] [Hide abstract]
    ABSTRACT: The layer-by-layer (LbL) technique is a wet chemical method for the assembly of ultrathin films, with thicknesses up to 100 nm. This method is based on the successive transfer of molecular layers to a solid substrate that is dipped into cationic and anionic solutions in an alternating fashion. The adsorption is mainly driven by electrostatic interactions so that many molecular and nanomaterial systems can be engineered under this method. Moreover, it is inexpensive, can be easily performed, and does not demand sophisticated equipment or clean rooms. The most explored use of the LbL technique is to build up molecular devices for chemical sensing and energy conversion. Both applications require ultrathin films where specific elements must be organized with high control of thickness and spatial distribution, preferably in the nanolength and mesolength scales. In chemical sensors, the LbL technique is employed to assemble specific sensoactive materials such as conjugated polymers, enzymes, and immunological elements onto appropriated electrodes. Molecular recognition events are thus transduced by the assembled sensoactive layer. In energy-conversion devices, the LbL technique can be employed to fabricate different device’s parts including electrodes, active layers, and auxiliary layers. In both applications, the devices’ performance can be fully modulated and improved by simply varying film thickness and molecular architecture. The present review article highlights the main features of the LbL technique and provides a brief description of different (bio)chemical sensors, solar cells, and organic light-emitting diodes enabled by the LbL approach.
    JOM: the journal of the Minerals, Metals & Materials Society 01/2013; 65(6). · 0.99 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study we report an experimental approach capable of tuning dipolar interactions in hybrid magnetic nanofilms produced via layer-by-layer assembly of positively-charged maghemite nanoparticles and sodium sulfonated polystyrene onto glass and silicon substrates. Morphological and magnetic properties of the as prepared nanofilms were determined by Raman spectroscopy, atomic force microscopy, conventional and SQUID magnetometry. Maghemite nanoparticles form densely packed layers with voids between particles being filled by polymeric material as observed in atomic force microscopy images. Magnetic hysteresis loops and zero-field-cooled/field-cooled magnetization curves reveal a superparamagnetic behavior at room temperature. The energy barrier for the magnetic moment reversal of the nanofilms has been determined from the frequency dependent ac susceptibility and is related to the gamma-Fe2O3 nanoparticles concentration used in the colloidal dispersion throughout film fabrication. Variations on the interparticle distances have a direct effect on the interparticle dipolar interactions. A less concentrated colloid gives rise to large separated nanoparticles inside the nanofilm with a consequent reduction on the energy barrier for the magnetic moment reversal. The fabrication process exploring the control of the nanoparticle concentration can thus be used to tune the magnetic dipolar interactions in the nanofilms.
    Journal of Nanoscience and Nanotechnology 08/2012; 12(8):6672-8. · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The internal morphology and magnetic properties of layer-by-layer assembled nanofilms of polyaniline (PANI) and maghemite (gamma-Fe2O3-7.5-nm diameter) were probed with cross-sectional transmission electron microscopy (TEM) and magnetization measurements (magnetic hysteresis loops, magnetization using zero-field cooled/field-cooled protocols, and ac magnetic susceptibility). Additionally, simulations of the as-produced samples were performed to assess both the nanofilm's morphology and the corresponding magnetic signatures using the cell dynamic system (CDS) approach and Monte Carlo (MC) through the standard Metropolis algorithm, respectively. Fine control of the film thickness and average maghemite particle-particle within this magnetic structure was accomplished by varying the number of bilayers (PANI/gamma-Fe2O3) deposited onto silicon substrates or through changing the concentration of the maghemite particles suspended within the colloidal dispersion sample used for film fabrication. PANI/gamma-Fe2O3 nanofilms comprising 5, 10, 25 and 50 deposited bilayers displayed, respectively, blocking temperatures (T-B) of 30, 35, 39 and 40 K and effective energy barriers (Delta E/k(B)) of 1.0 x 10(3), 2.3 x 10(3), 2.8 x 10(3) and 2.9 x 10(3) K. Simulation of magnetic nanofilms using the CDS model provided the internal morphology to carry on MC simulation of the magnetic properties of the system taking into account the particle-particle dipolar interaction. The simulated (using CDS) surface-surface particle distance of 0.5, 2.5 and 4.5 nm was obtained for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. The simulated (using MC) T-B values were 33.0, 30.2 and 29.5 K for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. We found the experimental (TEM and magnetic measurements) and the simulated data (CDS and MC) in very good agreement, falling within the same range and displaying the same systematic trend. Our findings open up new perspectives for fabrication of magnetic nanofilms with pre-established (simulated) morphology and magnetic properties.
    Journal of Nanoparticle Research 03/2012; 14(3). · 2.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The paper reports on the successful use of the quartz crystal microbalance technique to assess accurate kinetics and equilibrium parameters regarding the investigation of in situ adsorption of nanosized cobalt ferrite particles (CoFe(2)O(4)--10.5 nm-diameter) onto two different surfaces. Firstly, a single layer of nanoparticles was deposited onto the surface provided by the gold-coated quartz resonator functionalized with sodium 3-mercapto propanesulfonate (3-MPS). Secondly, the layer-by-layer (LbL) technique was used to build multilayers in which the CoFe(2)O(4) nanoparticle-based layer alternates with the sodium sulfonated polystyrene (PSS) layer. The adsorption experiments were conducted by modulating the number of adsorbed CoFe(2)O(4)/PSS bilayers (n) and/or by changing the CoFe(2)O(4) nanoparticle concentration while suspended as a stable colloidal dispersion. Adsorption of CoFe(2)O(4) nanoparticles onto the 3-MPS-functionalized surface follows perfectly a first order kinetic process in a wide range (two orders of magnitude) of nanoparticle concentrations. These data were used to assess the equilibrium constant and the adsorption free energy. Alternatively, the Langmuir adsorption constant was obtained while analyzing the isotherm data at the equilibrium. Adsorption of CoFe(2)O(4) nanoparticles while growing multilayers of CoFe(2)O(4)/PSS was conducted using colloidal suspensions with CoFe(2)O(4) concentration in the range of 10(-8) to 10(-6) (moles of cobalt ferrite per litre) and for different numbers of cycles n = 1, 3, 5, and 10. We found the adsorption of CoFe(2)O(4) nanoparticles within the CoFe(2)O(4)/PSS bilayers perfectly following a first order kinetic process, with the characteristic rate constant growing with the increase of CoFe(2)O(4) nanoparticle concentration and decreasing with the rise of the number of LbL cycles (n). Additionally, atomic force microscopy was employed for assessing the LbL film roughness and thickness. We found the film thickness increasing from about 20 to 120 nm while shifting from 3 to 10 CoFe(2)O(4)/PSS bilayers, using the 8.9 × 10(-6) (moles of cobalt ferrite per litre) suspension.
    Physical Chemistry Chemical Physics 12/2011; 13(48):21233-42. · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A multisensor system combining electronic tongue (ET) and nose (EN) was here developed to improve fuel quality control. Several impedance microelectrode sensors, with different geometries and sensoactive materials, were used separately and simultaneously in both liquid and vapor samples. The combined system significantly improved the substance discrimination compared to isolated ET and EN.
    09/2011;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper introduces a new approach for simulating magnetic properties of nanocomposites comprising magnetic particles embedded in a non-magnetic matrix, taking into account the 3D structure of the system in which particles' positions correctly mimic real samples. The proposed approach develops a multistage simulation procedure in which the size and distribution of particles within the hosting matrix is firstly attained by means of the Cell Dynamic System (CDS) model. The 3D structure provided by the CDS step is further employed in a Monte Carlo (MC) simulation of zero-field-cooled/field-cooled (ZFC/FC) and magnetic hysteresis loops ($M \times H$ curves) for the system. Simulations are aimed to draw a realistic picture of the as-produced ultra-thin films comprising maghemite nanoparticles dispersed in polyaniline. Comparison (ZFC/FC and $M \times H$ curves) between experiments and simulations regarding the maximum of the ZFC curve ($T_{\scriptsize MAX}$), remanence ($M_R/M_s$) and coercivity ($H_C$) revealed the great accuracy of the multistage approach proposed here while providing information about the system's morphology and magnetic properties. For a typical sample the value we found experimentally for $T_{\scriptsize MAX}$ (54 K) was very close to the value provided by the simulation (53 K). For the parameters depending on the nanoparticle clustering the experimental values were consistently lower ($M_R/M_s$ = 0.32 and $H_C$ = 210 Oe) than the values we found in the simulation ($M_R/M_s$ = 0.53 and $H_C$ = 274 Oe). Indeed, the approach introduced here is very promising for the design of real magnetic nanocomposite samples with optimized features.
    Journal of Magnetism and Magnetic Materials 08/2011; · 1.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Novel magnetic nanocomposite films with controlled morphology were produced via the electrostatic layer-by-layer assembly of cationic CoFe2O4 nanoparticles and anionic poly(3,4-ethylenedioxy thiophene)/poly(styrene sulfonic acid) (PEDOT:PSS) complex. The electrostatic interaction between nanoparticle and the polyelectrolyte complex ensured a stepwise growth of the nanocomposite film with virtually identical amounts of materials being adsorbed at each deposition cycle as observed by UV-vis spectroscopy. AFM images acquired under the tapping mode revealed a globular morphology with dense and continuous layers of nanoparticles with voids being filled with polymeric material.
    Journal of Magnetism and Magnetic Materials 01/2011; 323:1372-1377. · 1.83 Impact Factor
  • Guilherme S. Braga, Leonardo G. Paterno, Fernando J. Fonseca
    [Show abstract] [Hide abstract]
    ABSTRACT: An electronic tongue (ET) system consisting of conducting polymer sensors was employed to detect geosmin (GSM) in distilled water. GSM is a tainting compound and known to cause undesirable tastes and odors in water and aquaculture farming. Diluted solutions of GSM were prepared in distilled water at different concentrations. The electrical response (capacitance) of the sensors was analyzed using principal analysis component (PCA). The data obtained were separated into different clusters indicating a good sensibility of the ET system to this compound in distilled water. The ET showed signal saturation for concentrations higher than 300ng.L -1 . So far, the detection limit of our system is 25ng.L -1 . Nevertheless, close grouping
    01/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: A molecularly imprinted polymer (MIP) impedance-based sensor was employed to detect theophylline in distilled water. To evaluate its sensibility, impedance measurements were carried out in a diluted solution of theophylline (1mM) and distilled water using MIP and NIP (reference non-imprinted polymer) sensors. MIP showed higher sensitivity to theophylline than the NIP. This feature shows their suitability for developing an electronic tongue system for determination of methylxanthines.
    01/2011;
  • ECS Transactions. 01/2011; 39(1):307.
  • Source
    08/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study we describe the fabrication and characterization of nanocomposites consisting of layer-by-layer assembled polyaniline, sulfonated polystyrene, and maghemite nanoparticle layers. In order to assemble the starting components via electrostatic interaction, stable magnetic fluid containing maghemite nanoparticles (d approximately = 7 nm) with either positive or negative surface charges was used as source of nanoparticles for the layer-by-layer assembly. The structure, morphology, electrical and magnetic properties of such nanocomposite films were investigated by UV-Vis spectroscopy, atomic force microscopy, electrical, and magnetic measurements. The amount of PANI, PSS and maghemite nanoparticles within the nanocomposite films increased almost linearly with the number of deposited layers. Atomic force microscopy image of typical polyaniline/maghemite nanocomposites reveal nanoparticles adsorbed all over the film surface. The as-produced nanocomposite exhibits electrical conductivity and superparamagnetism behavior at room temperature, the latter confirmed by the absence of magnetic hysteresis.
    Journal of Nanoscience and Nanotechnology 04/2010; 10(4):2679-85. · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Efficient compact TiO2 films using different polyeleetrolytes are prepared by the layer-by-layer technique (LbL) and applied as an effective contact and blocking film in dye-sensitized solar cells (DSCs). The polyanion thermal stability plays a major role on the compact layers, which decreases back electron transfer processes and current losses at the FTO/TiO2 interface. FESEM images show that polyelectrolytes such is sodium sullonated polystyrene (PSS) and sulfonated lignin (SE), in comparison to poly(acrylic acid) (FAA), ensure an adequate morphology for the LbL TiO2 layer deposited before the mesoporous film, even triter the sintering step at 450 degrees C. The so treated photoanode in DSCs leads to a 30% improvement On the overall conversion efficiency. Electrochemical impedance spectroscopy (EIS) is employed to ascertain the role of die compact films with such polyelectrolytes. The significant increase in V-oc of the solar cells with adequate polyelectrolytes in the LbL TiO2 films shows their pivotal role in decreasing the electron recombination at the FTO surface and enhancing the electrical contact of FTO with the mesoporous TiO2 layer.
    Journal of Physical Chemistry C. 01/2010; 114(41):17954-17959.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Soybean is a product of great importance in the global economy and recognized by its great nourishing value with high protein content. In this work, a conducting polymer-based electronic tongue (ET) is employed to identify and discriminate five different soybeans cultivars with genetically distinct characteristics. Combination of electrical measurements and data analysis (PCA and PLS), permitted the ET system to discriminate the five different types of soybeans in accordance with a previous analysis performed by a human sensory panel.
    05/2009;

Publication Stats

88 Citations
34.81 Total Impact Points

Institutions

  • 2010–2013
    • University of Brasília
      • Institute of Physics
      Brasília, Federal District, Brazil
  • 2009
    • University of São Paulo
      • Instituto de Química (IQ) (São Paulo)
      São Paulo, Estado de Sao Paulo, Brazil
  • 2001–2002
    • Universidade Federal de São Carlos
      • Departamento de Engenharia de Materiais (DEMa)
      São Carlos, Estado de Sao Paulo, Brazil