Leonardo G. Paterno

Thermal and electrical properties of starch–graphene oxide nanocomposites improved by photochemical treatment

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.

Highly efficient photodynamic therapy colloidal system based on chloroaluminum phthalocyanine/pluronic micelles

Phthalocyanine derivatives comprise the second generation of photosensitizer molecules employed in photodynamic therapy (PDT) and have attracted much attention due to their outstanding photosensitizing performance. Most phthalocyanines are hydrophobic compounds that require association to drug delivery systems for clinical use. In this study, formulations of Pluronic F127 micelles incorporated with chloroaluminum phthalocyanine, or else F127/AlClPc, were produced at optimized conditions aiming at efficient and biocompatible PDT colloidal systems. Absorption/emission spectroscopies, as well as dynamic light scattering were performed to evaluate the optimum conditions for the F127 micelle formation and AlClPc incorporation. The micelles formation was attained with F127 concentrations ranging from 50 to 150mgmL(-1). At these conditions, AlClPc photosensitizer molecules were encapsulated into the hydrophobic micelle core and, therefore, readily solubilized in physiological medium (PBS pH 7.2). Encapsulation efficiency of about 90% resulted from different AlClPc concentrations. Identification of singlet oxygen production by irradiated F127/AlClPc formulations indicated good applicability for PDT. In vitro tests conducted with A549 human lung carcinoma cell line incubated with the F127/AlClPc formulations, at different AlClPc loadings, followed by only 18min of light irradiation (660nm LED, fluence of 25.3J/cm(2)), showed a cellular damage as high as 90% for rather low dosages of AlClPc (0.1-5.0μgmL(-1)). Further, no cytotoxicity occurred on non-irradiated cells. These findings suggest those F127/AlClPc formulations are highly promising for PDT applications, since they are easily prepared and the incubation and irradiation times are significantly shortened.

Photochemically-assisted synthesis of non-toxic and biocompatible gold nanoparticles.

This contribution describes the photochemically-assisted synthesis of aqueous colloidal suspensions of non-toxic and biocompatible spherical gold nanoparticles stabilized by branched polyethylenimine, or else Au-np-PEI. The method consists on 30min of photoexcitation (254nm, 16W) at room temperature of an aqueous diluted solution of chloroauric acid (HAuCl4) containing PEI. While the UV irradiation forms the [Au(3+)Cl4-]* excited species that succesively transforms into zero valent Au, PEI controls the nucleation step of nanoparticles formation. Varying the PEI to Au molar ratio permits one to tune the size of nanoparticles between 100nm to 8nm. The obtained colloidal suspensions display an intense plasmonic absorption band at 520-530nm and positive zeta potentials greater than +20mV. The cells viability for in vitro tests performed with human connective tissues and human breast adenocarcinoma (MCF-7) cell lines is over 80% and 90%, respectively, when they are incubated with Au-np-PEI formulations (25μgmL-1). The present photochemically-assisted synthesis is advantageous because it is fast and does not require for either hazardous or cytotoxic reductant agents and additional purification procedures.

A Hybrid Electronic Nose and Tongue for the Detection of Ketones: Improved Sensor Orthogonality Using Graphene Oxide-Based Detectors

In this contribution, the selectivity toward a diabetes biomarker was demonstrated by a non-specific impedance-metric chemical sensor array from blends of graphene oxide (GO)-based materials as a multivariate system for simultaneous aqueous and gaseous analyte investigation. The electrical impedance of bare graphene either oxidized or after reduction (RGO) displayed high specificity toward ammonia. The sensitivity of GO thin-film capacitance was 10.4 %/ppm of ammonia dissolved in ultrapure water, whereas RGO resistance featured 1.8 %/ppm to gaseous ammonia. However, composites with metal oxides, despite even providing a superior sensitivity to ammonia, completely alter the sign of sensor response to enable distinction of alcohols. Ceria and cyclodextrin allowed GO to operate in air at room temperature with improved stability and a faster response of approximately 60 s. These materials made for an increase in sensitivity to acetone of 11 and 3.2 times, respectively, compared to RGO. Therefore, GO-based composites, as well as the junction of electronic nose and tongue arrays were fundamental to enable the separation of acetone from alcohols and ammonia after principal component analysis.

A Combined Gas and Liquid Chemical Sensor Array for Fuel Adulteration Detection

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.

Molecular dynamics studies of amylose plasticized with Brazilian Cerrado oils: part I

1Laboratório de Estudos Estruturais Moleculares – LEEM, Instituto de Química – IQ, Universidade de Brasília – UnB, Campus Darcy Ribeiro, Brasília, DF, Brasil 2Laboratório de Pesquisa em Polímeros e Nanomateriais – LabPolN, Instituto de Química – IQ, Universidade de Brasília – UnB, Campus Darcy Ribeiro, Brasília, DF, Brasil 3Laboratoire d’Ingénierie des Biomolécules – LIBio, Ecole Nationale Supérieure d’Agronomie et des Industries Alimentaires – ENSAIA, Institut National Polytechnique de Lorraine – INPL, Université de Lorraine – UL, Vandœuvre-lès-Nancy, France

Quenching Effects of Graphene Oxides on the Fluorescence Emission and Reactive Oxygen Species Generation of Chloroaluminum Phthalocyanine

The photophysical behavior and reactive oxygen species (ROS) generation by chloroaluminum phthalocyanine (AlClPc) are evaluated by steady state absorption/emission, transient emission, and electron paramagnetic resonance spectroscopies in the presence of graphene oxide (GO), reduced graphene oxide (RGO), and carboxylated nanographene oxide (NGO). AlClPc and graphene oxides form a supramolecular structure stabilized by π-π interactions, which quantitatively quenches fluorescence emission and suppresses ROS generation. These effects occur even when graphenes are previously functionalized with Pluronic F-127. A small part of quenching is due to an inner filter effect, in which graphene oxides compete with AlClPc for light absorption. Nonetheless, most of the (static) quenching arises on the formation of a nonemissive ground state complex between AlClPc and graphene oxides. The efficiency of graphene oxides on the fluorescence quenching and ROS generation suppression follows the order: GO < NGO < RGO.

NANOMATERIAIS: CONVERSÃO DE ENERGIA SOLAR

A conversao de energia solar em eletricidade e uma das formas mais promissoras de producao de energia limpa a partir de fonte renovavel e uma solucao alternativa para atender a crescente demanda global por energia. Esse processo e realizado por dispositivos conhecidos como celulas solares. As celulas solares de terceira geracao, desenvolvidas a partir da decada de 1990, hoje atingem eficiencias muito proximas de celulas solares convencionais e chamam a atencao pelo custo baixo de producao e o carater inovador de empregar nanomateriais e conceitos de nanotecnologia para seu funcionamento. Nesse grupo se enquadram as celulas solares orgânicas (CSO) e as celulas sensibilizadas por corantes (CSSC). Neste capitulo serao apresentados os principios de funcionamento de uma celula solar, com enfase as CSO e CSSC. Uma descricao breve sobre o funcionamento de celulas fotoeletroquimicas para producao de combustiveis solares e feita ao termino do capitulo.

Nanostructured Polymer Films Doped with Cobalt‐ferrite Nanoparticles: a Raman Study

Nanocomposites of superparamagnetic iron oxide (SPIO) nanoparticles doped in polymeric matrices have been focus of intensive investigations due to potential applications in EMI shielding, spintronics and sensors. Apart of several methods, the layer-by-layer (LbL) technique for deposition of ultra-thin films is a simple but yet very powerful approach to produce such nanocomposites once it is capable of providing high control over film thickness and end properties. The LbL technique is based on the sequential adsorption driven by electrostatic attraction of different electrolyte materials, from a liquid phase onto solid substrates. SPIO nanoparticles prepared as either positively or negatively charged species can be sequentially adsorbed with common polyelectrolytes under this methodology. Among different characterization techniques, Raman spectroscopy is very suitable to provide information of the chemical structure of ultra-thin films own to its high sensitivity. SPIO nanoparticles exhibit characteristic Raman scattering modes which are associated to the typical crystalline structure of iron oxide materials. However, in some instances the polymeric matrix can screen the nanoparticle’s presence due to its fluorescence background. In the present study, we employ Raman spectroscopy to investigate the chemical structure of positively-charged cobalt ferrite nanoparticles doped in LbL films of poly(4-sodium styrene sulfonate) (PSS). In addition, transmission electron microscopy (TEM) is employed to evaluate the nanocomposite’s morphology. PSS was purchased from Sigma-Aldrich Co., USA and an aqueous solution (1.8 g L, pH 2) was prepared by dissolution in diluted HCl. CoFe2O4 nanoparticles were synthesized by co-precipitation of Co(II) and Fe(III) ions in aqueous alkaline medium according to the method reported previously. TEM image of the magnetic fluid (data not show) shows typical spherical nanoparticles with mean diameter of 2.98 ± 0.02 nm. The multilayered nanocomposite films were produced by the electrostatic LbL approach employing CoFe2O4 nanoparticles as cations and PSS as a polyanion. A gold coated glass slide used as substrate was modified with a monolayer of 3-MPA (3-mercaptopropionic acid) prior to film depositions. Substrates were first immersed into the cation’s dispersion for 3 min, then rinsed in a magnetic stirred HCl solution (pH 2) and dried with nitrogen flow. The substrate containing a layer of nanoparticles was subsequently immersed for 3 min into the PSS solution