Diego F. Acevedo

Functionalised conjugated materials as building blocks of electronic nanostructures

Two different approaches towards conjugated material (carbon nanotubes, conjugated polymers) functionalisation are presented: covalent bonding of functional groups and covalent interaction with soluble polymers. Covalent functionalisation of carbon nanotubes is made by reaction of the aromatic ring with aryl radicals, produced by reduction of diazonium ions. In the case of conducting polymers, covalent functionalisation is brought about by reaction of polyanilines with diazotized aromatic amines (including amino terminated azo dyes). The non covalent functionalisation of carbon nanotubes is made by wrapping the nanotubes with soluble conducting polyanilines. The functionalised materials are characterised by FTIR spectroscopy, X-ray diffraction, dynamic light scattering, ultraviolet-visible absorption and emission spectroscopy, transmission electron microscopy, cyclic voltammetry, differential electrochemical mass spectroscopy and conductivity measurements. The materials are to build ionic self assembled multilayers using a layer-by-layer deposition process. The charge transport and electrocatalytic behaviour of the assemblies, relevant to the application of the assemblies in nanostructured electrochemical biosensors, are evaluated using different redox molecules and/or its intrinsic electroactivity as probes.

Synthesis, properties and aplications of functionalized polyanilines

Novos polimeros condutores funcionalizados foram sintetizados a partir de modificacoes das reacoes de acoplamento polianilina-diazonio, adicao nucleofilica e N-nitrosacao. O acoplamento de diazonio fornece polimeros modificados que sao eletroativos e soluveis em solventes comuns. Adicao nucleofilica tambem pode ser usada para modificacoes da polianilina. Polimeros modificados pela adicao de tiois, carbânions e acidos arilsulfinicos sao apresentados. A adicao nucleofilica de acidos arilsulfinicos a polianilina oxidada mostrou ser controlada pelos estados de oxidacao e/ou protonacao do polimero. A N-nitrosacao de polianilina tambem e possivel, produzindo material soluvel em solventes comuns. Esta reacao pode ser revertida por tratamento acido. A reacao de nitrosacao reversivel foi usada para controlar processos litograficos e fotolitograficos de deposicao de padroes de PANI.

Smart surfaces: reversible switching of a polymeric hydrogel topography

Patterns imprinted on smart surfaces are fabricated by direct laser interference patterning (DLIP) of thick films based on poly(N-isopropylacrylamide) (PNIPAM) doped with suitable dyes. Optical and atomic force (AFM) microscopy images reveal that the pattern imprinted on the dry hydrogel film (line-arrays) becomes flat due to swelling of the hydrogel upon immersion in water. The pattern re-emerges after drying the hydrogel. Heating the hydrogel above the phase transition temperature of PNIPAM (ca. 32 °C) also restores the pattern by hydrogel volume collapse. This behaviour suggests that this patterning technique would allow us to produce surfaces useful for technological application.

Cysteine modified polyaniline films improve biocompatibility for two cell lines

This work focuses on one of the most exciting application areas of conjugated conducting polymers, which is cell culture and tissue engineering. To improve the biocompatibility of conducting polymers we present an easy method that involves the modification of the polymer backbone using l-cysteine. In this publication, we show the synthesis of polyaniline (PANI) films supported onto Polyethylene terephthalate (PET) films, and modified using cysteine (PANI-Cys) in order to generate a biocompatible substrate for cell culture. The PANI-Cys films are characterized by Fourier Transform infrared and UV-visible spectroscopy. The changes in the hydrophilicity of the polymer films after and before the modification were tested using contact angle measurements. After modification the contact angle changes from 86°±1 to 90°±1, suggesting a more hydrophylic surface. The adhesion properties of LM2 and HaCaT cell lines on the surface of PANI-Cys films in comparison with tissue culture plastic (TCP) are studied. The PANI-Cys film shows better biocompatibility than PANI film for both cell lines. The cell morphologies on the TCP and PANI-Cys film were examined by florescence and Atomic Force Microscopy (AFM). Microscopic observations show normal cellular behavior when PANI-Cys is used as a substrate of both cell lines (HaCaT and LM2) as when they are cultured on TCP. The ability of these PANI-Cys films to support cell attachment and growth indicates their potential use as biocompatible surfaces and in tissue engineering.

Organic Chemistry of Polyanilines: Tailoring Properties to Technological Applications~!2008-08-19~!2008-09-11~!2008-11-28~!

The use of organic chemistry reactions to introduce additional functional groups on polyanilines is described. Among the reactions discussed are: electrophilic aromatic substitution, nucleophilic addition to the aromatic rings, nu- cleophilic substitution on the amine groups and reactions on pendant groups. The use of combinatorial chemistry tech- niques, by coupling of combinatorially synthesised diazonium salts with polyaniline, to produce a functionalized polyani- lines library is also reviewed. The modification of polyaniline introduces or alters different properties of the materials: solubility, self-doping and redox coupled ion exchange. The tailoring of those properties to technical applications is there- fore examined.

IgY against enterotoxigenic Escherichia coli administered by hydrogel-carbon nanotubes composites to prevent neonatal diarrhoea in experimentally challenged piglets

In previous studies, the applicability of polymeric hydrogels for the protection of egg yolk immunoglobulin (IgY) against simulated gastric conditions was established. Thereafter, the performance of the hydrogels was improved with the addition of chitosan wrapped carbon nanotubes and the in vitro toxicity for porcine intestinal cells of these nanocomposites was assessed. The objective of the present study was to evaluate in vivo the protective efficacy of the nanocomoposite matrix for IgY when the immunoglobulin is used against enterotoxigenic Escherichia coli (ETEC) in challenged piglets. Groups of piglets orally challenged with 10(11)CFU/mL of ETEC were treated with non-protected and protected IgY. The clinical response of each group was monitored and evaluated in terms of dehydration, rectal temperature, faecal consistency score and body weight gain. Blood parameters and histological aspects were also studied. The results showed that treatment of infected piglets with protected IgY reduced significantly the severity of diarrhea. Non-protected IgY group show a lower recovery rate. Blood parameters and histological aspects were normal in both groups. Collectively, these results support previous in vitro studies showing that the nanocomposites can be an effective method of IgY protection against gastric inactivation.

Fabrication of highly ordered arrays of platinum nanoparticles using direct laser interference patterning

Highly ordered electrode arrays composed of lines of platinum nanoparticles deposited onto gold substrates have been made by direct laser interference patterning of polyaniline thin films, followed by electrochemical deposition of platinum nanoparticles. Nanostructured arrays of electrocatalytic platinum particles are built in that way.

Biosorption of aluminum through the use of non-viable biomass of Pseudomonas putida

Living and non-living biomass of Pseudomonas putida A (ATCC 12633) was used as biosorbent for the removing of Al(3+) from aqueous solutions. The process was stable with time, efficient at pH 4.3 and between 15°C and 42°C. Two isotherms models were applied to describe the interaction between the biosorbent and Al(3+). Non-living biomass of P. putida A (ATCC 12633) was found to be the most efficient at adsorbing Al(3+) with a maximum sorption capacity of 0.55mg Al(3+)/gr adsorbent and with 36×10(5) binding sites of Al(3+)/microorganisms. Infrared spectroscopy analysis shows that the biosorbent present some vibrational band of functional groups that change in presence of Al(3+): hydroxyl, carboxyl and phosphate. Considering that Al(3+) binds to the phosphate group of phosphatidylcholine, non-viable biomass of P. putida PB01 (mutant lacking phosphatidylcholine) was used. Aluminum adsorption of the parental strain was 30 times higher than values registered in P. putida PB01 (36×10(5) sites/microorganism vs 1.2×10(5) sites/microorganism, respectively). This result evidenced that the absence of phosphatidylcholine significantly affected the availability of the binding sites and consequently the efficiency of the biomass to adsorb Al(3+).

Electroanalysis using modified hierarchical nanoporous carbon materials

The role of the electrode nanoporosity in electroanalytical processes is discussed and specific phenomena (slow double layer charging, local pH effects) which can be present in porous electrode are described. Hierarchical porous carbon (HPC) materials are synthesized using a hard template method. The three dimensional carbon porosity is examined using scanning electron microscopy on flat surfaces cut using a focused ion beam (FIB-SEM). The electrochemical properties of the HPC are measured using cyclic voltammetry, AC impedance, chronoamperometry and Probe Beam Deflection (PBD) techniques. Chronoamperometry measurements of HPC seems to fit a transmission line model. PBD data show evidence of local pH changes inside the pores, during double layer charging. The HPC are modified by in situ (chemical or electrochemical) formation of metal (Pt/Ru) or metal oxide (CoOx, Fe3O4) nanoparticles. Additionally, HPC loaded with Pt decorated magnetite (Fe3O4) nanoparticles is produced by galvanic displacement. The modified HPC materials are used for the electroanalysis of different substances (CO, O2, AsO3(-3)). The role of the nanoporous carbon substrate in the electroanalytical data is evaluated.

Large area fabrication of tuned polystyrene/poly(methylmethacrylate) periodic structures using laser interference patterning.

The fabrication of advanced architectures in poly(methylmethacrylate-co-styrene) (PMMA-S) copolymers (ranging from 12 to 66% mol content of methylmethacrylate) using direct laser interference patterning is reported. For all copolymer compositions, two different regimes were observed. At low laser intensities, the irradiated surfaces swell up due to the formation of microbubbles that result from the degradation of the methylmetacrylate (MMA) component. While laser ablation produces concave holes, the swelling process permits fabrication of convex hemispherical dots. At higher intensities the bubbles release from the surface forming a periodic micropored structure. In addition, the laser fluence necessary to swell the polymeric surface (swelling threshold) does not depend on polymer composition, while the ablation threshold, which determines the transition to the periodic micropored structure, strongly depends on the MMA content. This observation can be explained by the mechanical and chemical properties of the copolymer. The method provides a unique way to produce periodical structures protruding from the polymer surface.