Biomedical subjects

Osvaldo N Oliveira

Publications and source records attributed to Osvaldo N Oliveira.

At least 19 recordsLinked to original sources

PubMed2006

Physicochemical properties and sensing ability of metallophthalocyanines/chitosan nanocomposites.

Electroactive nanostructured films of chitosan (Ch) and tetrasulfonated metallophthalocyanines containing nickel (NiTsPc), copper (CuTsPc), and iron (FeTsPc) were produced via the electrostatic layer-by-layer (LbL) technique. The multilayer formation was monitored with UV-vis spectroscopy by measuring the increase of the Q-band absorption from metallophthalocyanines. Results from transmission and reflection infrared spectroscopy suggested specific interactions between SO(3)(-) groups from metallophthalocyanines and NH(3)(+) from chitosan. The electroactive multilayered films assembled onto an ITO electrode were characterized by cyclic voltammetry, with Ch/NiTsPc films showing higher stability and well-defined voltammograms displaying reversible redox peaks at 0.80 and 0.75 V. These films could be used to detect dopamine (DA) in the concentration range from 5.0 x 10(-6) to 1.5 x 10(-4) mol L(-1). Also, ITO-(Ch/NiTsPc)(n)() electrodes showed higher electrocatalytic activity for DA oxidation when compared with a bare ITO electrode. On the other hand, only the Ch/FeTsPc and Ch/CuTsPc modified electrodes could distinguish between DA and ascorbic acid. These results demonstrate that versatile electrodes can be prepared by incorporation of different metallophthalocyanine molecules in LbL films, which may be used in bioanalytical applications.

Journal Article↗

PubMed2006

Interactions of chlorpromazine with phospholipid monolayers: effects of the ionization state of the drug.

Molecular dynamics simulations have been performed to investigate the interactions between chlorpromazine (CPZ) and Langmuir monolayers of the zwitterionic dipalmitoylphosphatidylcholine (DPPC) and the anionic dipalmitoylphosphatidylglycerol (DPPG). Simulations for a fixed surface density and different charge states - neutral and protonated CPZ - were able to capture important features of the CPZ-phospholipid monolayer interaction. Neutral CPZ is predominantly found in the hydrophobic tail region, whereas protonated CPZ is located at the lipid-water interface. Specific interactions (hydrogen bonds) between protonated CPZ and the lipid head groups were found for both zwitterionic and anionic monolayers. We computed lipid tail order parameters and investigated the effects of the drug upon tail ordering. We also computed electrostatic surface potentials and found qualitative good agreement with experimental results.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Fabrication of phytic acid sensor based on mixed phytase-lipid Langmuir-Blodgett films.

This paper reports the surface activity of phytase at the air-water interface, its interaction with lipid monolayers, and the construction of a new phytic acid biosensor on the basis of the Langmuir-Blodgett (LB) technique. Phytase was inserted in the subphase solution of dipalmitoylphosphatidylglycerol (DPPG) Langmuir monolayers, and its incorporation to the air-water interface was monitored with surface pressure measurements. Phytase was able to incorporate into DPPG monolayers even at high surface pressures, ca. 30 mN/m, under controlled ionic strength, pH, and temperature. Mixed Langmuir monolayers of phytase and DPPG were characterized by surface pressure-area and surface potential-area isotherms, and the presence of the enzyme provided an expansion in the monolayers (when compared to the pure lipid at the interface). The enzyme incorporation also led to significant changes in the equilibrium surface compressibility (in-plane elasticity), especially in liquid-expanded and liquid-condensed regions. The dynamic surface elasticity for phytase-containing interfaces was investigated using harmonic oscillation and axisymmetric drop shape analysis. The insertion of the enzyme at DPPG monolayers caused an increase in the dynamic surface elasticity at 30 mN m(-)(1), indicating a strong interaction between the enzyme and lipid molecules at a high-surface packing. Langmuir-Blodgett (LB) films containing 35 layers of mixed phytase-DPPG were characterized by ultraviolet-visible and fluorescence spectroscopy and crystal quartz microbalance nanogravimetry. The ability in detecting phytic acid was studied with voltammetric measurements.

6-Phytase↗

PubMed2006

Enhanced charge transport and incorporation of redox mediators in layer-by-layer films containing PAMAM-encapsulated gold nanoparticles.

In this work, we exploit the molecular engineering capability of the layer-by-layer (LbL) method to immobilize layers of gold nanoparticles on indium tin oxide (ITO) substrates, which exhibit enhanced charge transfer and may incorporate mediating redox substances. Polyamidoamine (PAMAM generation 4) dendrimers were used as template/stabilizers for Au nanoparticle growth, with PAMAM-Au nanoparticles serving as cationic polyelectrolytes to produce LbL films with poly(vinylsulfonic acid) (PVS). The cyclic voltammetry (CV) of ITO-PVS/PAMAM-Au electrodes in sulfuric acid presented a redox pair attributed to Au surface oxide formation. The maximum kinetics adsorption is first-order, 95% of the current being achieved after only 5 min of adsorption. Electron hopping can be considered as the charge transport mechanism between the PVS/PAMAM-Au layers within the LbL films. This charge transport was faster than that for nonmodified electrodes, shown by employing hexacyanoferrate(III) as the surface reaction marker. Because the enhanced charge transport may be exploited in biosensors requiring redox mediators, we demonstrate the formation of Prussian blue (PB) around the Au nanoparticles as a proof of principle. PAMAM-Au@PB could be easily prepared by electrodeposition, following the ITO-PVS/ PAMAM-Au LbL film preparation procedure. Furthermore, the coverage of Au nanoparticles by PB may be controlled by monitoring the oxidation current.

Journal Article↗

PubMed2006

The effect of the layer structure on the activity of immobilized enzymes in ultrathin films.

The molecular engineering capability of the layer-by-layer (LbL) method for fabricating thin films has been exploited in order to immobilize glucose oxidase (GOD) in films with alternating layers of chitosan. Chitosan was proven a good scaffolding material, as GOD molecules preserved their catalytic activity towards glucose oxidation. Using electrochemical measurements, we showed that chitosan/GOD LbL films can be used to detect glucose with a limit of detection of 0.2 mmol l-1 and an activity of 40.5 microA mmol-1 L microg-1, which is highly sensitive when compared to other sensors in previous reports in the literature. The highest sensitivity of the LbL film was achieved when only the top layer contained GOD, thus indicating that GOD in inner layers did not contribute to glucose oxidation, probably because it hampers analyte diffusion and electron transport through the deposited layers. This may be explained by the dense packing of GOD molecules in the LbL films with chitosan, as inferred from estimates of the amount of GOD adsorbed per layer using a quartz crystal microbalance.

Aspergillus niger↗

PubMed2006

The role of Azopolymer/Dendrimer layer-by-layer film architecture in photoinduced birefringence and the formation of surface-relief gratings.

The fabrication of nanostructured layer-by-layer (LbL) films strives for molecular control of the film properties directly connected with modifications in the film architecture. In the present report, the photoinduced birefringence and formation of the surface-relief gratings in LbL films obtained with an azopolymer (PS119) are shown to be strongly affected by the generation of the dendrimer employed in the alternating layers. Stronger adsorption of PS119 occurred when polypropylenimine tetrahexacontaamine dendrimer (DAB) of higher generations is used, due to a larger number of sites available to interact with azochromophores in PS119. In contrast, the photoinduced birefringence for LbL films made with the generation 1 dendrimer (DABG1) was higher, which can be explained by weaker interactions between adjacent layers. Strong interactions in LbL films consisting of PS119 and generation 3 or 5 dendrimers restrict the chromophore mobility, leading to a smaller birefringence. The interpretation is supported by the fact that surface-relief gratings with larger amplitudes were obtained for 35-bilayer films of DABG1/PS119 (31 nm) in comparison with films from DABG5/PS119 (5 nm). These gratings were formed with mass transport arising from a light-driven mechanism, as photoinscription was successful only with p-polarized light and not with s-polarized light.

Journal Article↗

PubMed2006

Molecular dynamics simulations of neutral chlorpromazine in zwitterionic phospholipid monolayers.

Molecular dynamics simulations have been performed to investigate the interactions between chlorpromazine (CPZ), a neuroleptic drug used in the treatment of psychiatric disorders, and dipalmitoylphosphatidylcholine (DPPC), a zwitterionic phospholipid, in Langmuir monolayers. The results from simulations carried out at different monolayer surface densities were able to capture important features of the CPZ-lipid interaction. We find that neutral (unprotonated) CPZ is preferentially located in the lipid tail region of the phospholipids, in little contact with the aqueous phase, and that the orientation of its rigid ring structure and tail conformation vary with lipid surface density. CPZ is found to promote ordering of the lipid tails for all surface densities because of a reduction in the effective surface area per lipid upon addition of the drug. Similar effects have been observed in previous studies of cholesterol in DPPC monolayers, in which lipid tails were seen to order around the solute. This feature, however, is quite distinct from what we observe for the most dense monolayer considered here (area per lipid of 50 A(2)), for which we find that CPZ promotes a local distortion of the lipid tails in its immediate vicinity and a concomitant ordering of lipid tails located further away from the solute. This view is further supported by the results obtained for an approximated nonlinear vibrational sum frequency generation susceptibility, which showed greater tail disorder close to CPZ.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2006

Thermal stability of poly(o-methoxyaniline) layer-by-layer films investigated by neutron reflectivity and UV-VIS spectroscopy.

Neutron reflectivity measurements were used to investigate the thermal stability of layer-by-layer (LBL) films of poly(o-methoxyaniline) (POMA), which was probed by increasing the temperature up to 80 degrees C of a D2O solution in contact with the LBL films. The study was made possible by adsorbing POMA layers on a PEI/(PSS/PAH)5/PSS LBL film template, leading to less rough POMA layers in comparison with the POMA/poly(vinylsulfonic acid sodium salt) (PVS) LBL films adsorbed directly on glass and silicon substrates. While the latter yielded almost fringeless neutron reflectivity curves due to the large roughness, the fitting of the data for POMA films adsorbed onto the template film and UV-vis measurements indicated that the topmost layer is affected for films heated in solution up to 80 degrees C. This is essentially the same thermal stability of LBL films from the template films made with conventional polyelectrolytes. A decrease in thickness of approximately 10 A was inferred when the solution temperature increased from 25 degrees C to 80 degrees C, which was maintained when the sample was cooled back to 25 degrees C. This decrease, observed for solutions of pH 3 and pH 8, is consistent with thermally-stimulated desorption and was corroborated by UV-VIS absorption experiments. The unexpected stability of the POMA layer at pH 8 is attributed to the layer-by-layer structure of the films that allows POMA to remain doped, in its salt emeraldine form, even at high pH.

Aniline Compounds↗

PubMed2005

Interaction of small amounts of bovine serum albumin with phospholipid monolayers investigated by surface pressure and atomic force microscopy.

The influence of small amounts of bovine serum albumin (BSA) (nM concentration) on the lateral organization of phospholipid monolayers at the air-water interface and transferred onto solid substrates as one-layer Langmuir-Blodgett (LB) films was investigated. The kinetics of adsorption of BSA onto the phospholipid monolayers was monitored with surface pressure isotherms in a Langmuir trough, for the zwitterionic dipalmitoylphosphatidyl ethanolamine (N,N-dimethyl-PE) and the anionic dimyristoylphosphatidic acid (DMPA). A monolayer of N,N-dimethyl-PE or DMPA incorporating BSA was transferred onto a solid substrate using the Langmuir-Blodgett technique. Atomic force microscopy (AFM) images of one-layer LB films displayed protein-phospholipid domains, whose morphology was characterized using dynamic scaling theories to calculate roughness exponents. For DMPA-BSA films the surface is characteristic of self-affine fractals, which may be described with the Kardar-Parisi-Zhang (KPZ) equation. On the other hand, for N,N-dimethyl-PE-BSA films, the results indicate a relatively flat surface within the globule. The height profile and the number and size of globules varied with the type of phospholipid. The overall results, from kinetics of adsorption on Langmuir monolayers and surface morphology in LB films, could be interpreted in terms of the higher affinity of BSA to the anionic DMPA than to the zwitterionic N,N-dimethyl-PE. Furthermore, the effects from such small amounts of BSA in the monolayer point to a cooperative response of DMPA and N,N-dimethyl-PE monolayers to the protein.

Adsorption↗

PubMed2005

Optical storage and surface-relief gratings in azobenzene-containing nanostructured films.

This paper brings an overview of photoisomerization-derived properties in azobenzene-containing nanostructured films produced with the Langmuir-Blodgett (LB) and layer-by-layer (LbL) methods. Emphasis was placed on the optical storage and formation of surface-relief gratings (SRGs), where the distinctive properties of the nanostructured films were highlighted. For optical storage, in particular, a discussion was made of the higher birefringence induced in LB films from azopolymers due to their organized nature, and of the strong effects from ionic interactions on the photoisomerization of azochromophores in LbL films. The molecular-level control of film properties in the LbL films is described as being responsible for the varied behavior observed in the photoinscription of SRGs, which may involve considerable level of photodegradation depending on the film fabrication conditions and materials used.

Azo Compounds↗

PubMed2005

Catechol biosensing using a nanostructured layer-by-layer film containing Cl-catechol 1,2-dioxygenase.

The detection of aromatic compounds from pesticides and industrial wastewater has become of great interest, since these compounds withstand chemical oxidation and biological degradation, accumulating in the environment. In this work, a highly sensitive biosensor for detecting catechol was obtained with the immobilization of Cl-catechol 1,2-dioxygenase (CCD) in nanostructured films. CCD layers were alternated with poly(amidoamine) generation 4 (PAMAM G4) dendrimer using the electrostatic layer-by-layer (LbL) technique. Circular dichroism (CD) measurements indicated that the immobilized CCD preserved the same conformation as in solution. The thickness of the very first CCD layers in the LbL films was estimated at ca. 3.6 nm, as revealed by surface plasmon resonance (SPR). PAMAM/CCD 10-bilayer films were employed in detecting diluted catechol solutions using either an optical or electrical approach. Due to the mild immobilization conditions employed, especially regarding the pH and ionic strength of the dipping solutions, CCD remained active in the films for periods longer than 3 weeks. The optical detection comprised absorption experiments in which the formation of cis-cis muconic acid, resulting from the reaction between CCD and catechol, was monitored by measuring the absorbance at 260 nm after film immersion in catechol solutions. The electrical detection was carried out using LbL films deposited onto gold-interdigitated electrodes immersed in aqueous solutions at different catechol concentrations. Using impedance spectroscopy in a broad frequency range (1Hz-1kHz), we could detect catechol in solutions at concentrations as low as 10(-10) M.

Adsorption↗

PubMed2005

Immobilization of humic acid in nanostructured layer-by-layer films for sensing applications.

Humic acids (HAs), naturally occurring biomacromolecules, were incorporated into nanostructured polymeric films using the layer-by-layer (LbL) technique, in which HA layers were alternated with layers of poly(allylamine hydrochloride) (PAH). Atomic force microscopy (AFM) revealed very smooth films, with mean roughness varying from 0.89 to 1.19 nm for films containing 5 and 15 PAH/HA bilayers, respectively. The films displayed electroactivity, with the presence of only one reduction peak at ca. 0.675 V (vs Ag/AgCl). Such a well-defined electroactivity allowed the films to be used as highly sensitive pesticide sensors, with detection of pentachlorophenol (PCP) in solutions at concentrations as low as 10(-9) mol L(-1).

Biosensing Techniques↗

PubMed2005

Electrochemical and electrochromic properties of layer-by-layer films from WO(3) and chitosan.

The design of improved materials for electrochromic applications now involves extensive use of novel composites, thus requiring an investigation of the mechanisms responsible for electrochromism in these structures. Using films of WO(3) and chitosan produced with the layer-by-layer (LBL) technique, we demonstrate that characteristics such as the number of electrochemical active sites (K), the molar absorption coefficient (epsilon), and the electrochromic efficiency (eta) can be obtained using the quadratic logistic equation (QLE). The complexation ability between chitosan and WO(3) allowed the growth of visually uniform multilayers of the composite, with the same amount of material adsorbed in each deposition cycle. By fitting the absorbance changes (DeltaA) resulting from the electronic intervalence transfer from W(V) to W(VI) sites in four-bilayer LBL films of WO(3)/chitosan and WO(3)/chitosan with ethanol in the precursor dispersion, K was estimated to be ca. 5.5 x 10(-8) mol cm(-2) and 3.6 x 10(-8) mol cm(-2), respectively. The molar absorption coefficient and electrochromic efficiency vary with the charge injected because of the saturation of W(V) sites and the dissipation and feedback effects implicit in the QLE associated with ion-network interactions, such as the proton trapping effect. The LBL film of WO(3)/chitosan showed a smaller molar absorption coefficient and electrochromic efficiency than that containing ethanol because of a greater proton trapping effect for the LBL film with no ethanol. This enhanced trapping effect was seen as a decrease in the electronic flux involved in intervalence transfer in electrochemical impedance spectroscopy experiments.

Journal Article↗

PubMed2005

Spectroscopic studies of the intermolecular interactions of Congo red and tinopal CBS with modified cellulose fibers.

The adsorption of Congo red and tinopal CBS dyes on cellulose fibers was investigated using electronic absorption and fluorescence spectroscopies. Hydrogen bonds appear to be relevant for the dye-fiber interactions as indicated by the solvatochromism of Congo red in water, methanol, and dimethyl sulfoxide solutions, and when adsorbed on cellulose fibers. We also demonstrate that electrostatic interactions play an important role in the dye-medium interaction, through the analysis of absorption spectra of Congo red and fluorescence spectra of tinopal in aqueous solutions containing salt and in layer-by-layer nanostructured films with poly(allylamine hydrochloride). For instance, dye adsorption was enhanced when salt was added to the dipping solution, which was explained by the synergistic effect between the conformational changes of the cellulose and changes in the solvation layer around the cellulose chains and around dye molecules. On the basis of the fluorescence results for tinopal CBS, we inferred that dye aggregation is not relevant for adsorption on the fibers. In addition, fluorescence spectroscopy is proven very sensitive for studying the organization of dye molecules in layer-by-layer films, particularly those undergoing irreversible structural changes.

Benzenesulfonates↗

PubMed2005

Surface-enhanced raman scattering on dendrimer/metallic nanoparticle layer-by-layer film substrates.

In this paper, the fabrication, characterization, and application of unique layer-by-layer (LBL) films of dendrimers and metallic nanoparticles is reported. Silver nanoparticles (d = approximately 20 nm) are produced in solution by sodium citrate reduction and incorporated into thin films with generation 1 and 5 DAB-Am dendrimers (polypropylenimine dendrimers with amino surface groups) by the LBL technique. The resulting nanocomposite films are characterized by UV-visible surface plasmon absorption and atomic force microscopy (AFM) measurements, and employed as substrates for surface-enhanced Raman scattering (SERS) of 2-naphthalenethiol. Through variation of the molecular size (dendrimer generation) and concentration of the cross-linker used, as well as the number of layers produced, the optical properties of several different possible architectures are studied. In the films, Ag nanoparticles are shown to be effectively immobilized and stabilized with increased control over their spacing and aggregation. Moreover, the films are shown to be excellent substrates for SERS measurements, demonstrating significant enhancement capability. As expected, large electromagnetic enhancement of Raman scattering signals is found to be strongly dependent on interparticle coupling between neighboring metallic nanoparticles. Finally, the possibility of detecting SERS signals from architectures with intervening layers between the metal nanoparticles and analyte molecules is explored. It is shown that although there are decreases in intensity with increasing number of intervening layers (as is expected from the distance dependence of SERS), electromagnetic enhancement is still able to function at these distances, thus offering the possibility of developing sensors with external layers that are chemically selective for specific analytes.

Journal Article↗

PubMed2005

Morphology characterization of layer-by-layer films from PAH/MA-co-DR13: the role of film thickness.

We report on the use of dynamic scale theory and fractal analyses in the study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed on glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The granular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains. The growth outside the grains was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of ca. 2.6. One could expect that inside the grains the morphology would be close to a Euclidian surface with fractal dimension of ca. 2 for any growth stage. The latter, however, was observed only for thicker films containing more than 10 bilayers. For thinner films the morphology was well described by a self-affine fractal. Such dependence of the growth behavior with the film thickness is associated with a more complete coverage of adsorption sites in thicker films due to diffusion of polymer molecules.

Azo Compounds↗

PubMed2005

Molecular-level control of the photoluminescence from PPV nanostructured films.

The fabrication of varied molecular architectures in layer-by-layer (LbL) films is exploited to control the photoluminescence (PL) of poly(p-phenylene vinylene) (PPV) in an unprecedented way. This was achieved by controlling the Förster energy transfer between PPV layers (donors) and layers of a commercial azodye, Brilliant Yellow (BY) (acceptors). Energy transfer was controlled by inserting spacer layers of inert polymers between PPV and BY layers and by photoaligning the BY molecules via trans-cis-trans isomerization. The PPV/BY LbL films displayed polarized PL whose intensity could be varied almost continuously by changing the time of photoalignment, which was carried out by impinging a linearly polarized laser light simultaneously to the PL experiments. For PPV/BY films with no spacer layers, PL was completely quenched, but its intensity increased with the number of spacing layers. Further increase in PL was obtained by photoaligning the BY molecules perpendicularly to the PPV molecules. This minimizes energy transfer, since Förster processes are directional, dipole-dependent resonant transfers. Energy transfer is also controlled by imparting a preferential orientation of the PPV chains on PPV/BY LbL films deposited onto flexible Teflon substrates that may be stretched.

Journal Article↗

PubMed2005

Morphological and structural characteristics of diazo dyes at the air-water interface: in situ Brewster angle microscopy and polarized UV/vis analysis.

A morphological analysis is presented for Langmuir films of the diazo dyes Sudan 4 (S4), Sudan 3 (S3), and Sudan red (SR), using Brewster angle microscopy. Stable nonmonomolecular structures are formed at the air-water interface denoted as a plateau in the pressure-area isotherms. Monolayer domains are evident by the contrastless image even before the pressure onset, which grow in size until it reached a condensed monolayer. This behavior resembles that of Langmuir films from simple aromatic fatty acids. Films from all the azo dyes display similar features, according to the surface potential isotherms and in situ polarized UV/vis spectroscopy except for the larger area per molecule occupied by S4 and SR. This is attributed to the presence of CH(3) groups that cause steric hindrance modifying the organization of diazo dye molecules at the air-water interface. UV/vis polarized absorption spectroscopy showed preferential orientation of S4 and S3 on the water surface, while SR molecules lie isotropically. For these three diazo dyes, film absorption was negligible at very large areas per molecule, becoming nonzero only at a critical area coinciding with the onset of surface potential. The critical area is ascribed to the formation of a H-bonded network between water molecules and diazo dye headgroups.

Journal Article↗