Introdução à nanotecnologia.

BREVE HISTÓRICO SOBRE A NANOTECNOLOGIA E NANOCIÊNCIA A possibilidade de se manipular e controlar coisas ?muito pequenas? foi vislumbrada há mais de seis décadas pelo físico norte-americano Richard Feynman (ganhador do prêmio Nobel de Física em 1985), em sua seminal palestra ministrada durante o encontro da Sociedade Americana de Física em Pasadena, Estados Unidos. Nessa palestra, Feynman conjecturou que não haveria limites físicos para, por exemplo, se escrever na cabeça de um alfinete, sugerindo que ?havia muito espaço lá embaixo?.1 Apesar da manipulação da matéria na escala atômica ou nanométrica já existir, sua comprovação experimental esbarrava na necessidade do desenvolvimento de técnicas avançadas de microscopia que permitissem a visualização e a manipulação de átomos e moléculas e seus arranjos. Em 1974 o professor Norio Taniguchi associou o conceito "nano" à tecnologia, época em que já havia se tornado possível a obtenção de materiais na escala nanométrica, devido principalmente à evolução dos microscópios eletrônicos.2 De fato, um dos feitos mais importantes para o desenvolvimento da nanociência foi a invenção, em 1981, do microscópio de tunelamento por varredura (STM, do inglês scanning tunneling microscope) pelos cientistas Gerd Binning e Heinrich Rohrer na IBM de Zurich, Suíça. A descoberta permitiu o imageamento bidimensional de superfícies condutoras com resolução atômica, e ambos os pesquisadores foram agraciados com o prêmio Nobel de Física em 1986 pela importante descoberta.1 Alguns anos depois, Binning e colaboradores desenvolveram o microscópio de força atômica (AFM, do inglês atomic force microscope), que não demandava utilização de corrente elétrica no imageamento e possibilitava varrer qualquer tipo de superfície, fosse ela condutora elétrica ou não.3 Desde então, muito se tem avançado no desenvolvimento de técnicas e tecnologias empregadas na formação e caracterização de diversos tipos de nanoestruturas, bem como em investigações sobre muitas de suas interessantes propriedades e potenciais aplicações, em áreas diversas como eletroeletrônica, medicina, agricultura e pecuária e meio ambiente. Nesse contexto, dois termos são conhecidos e vêm sendo cada vez mais difundidos em nosso cotidiano: a nanociência e a nanotecnologia. Enquanto a nanociência diz respeito ao estudo e conhecimento dos fenômenos que envolvem a manipulação, seja no desenho, controle e modificação dos materiais nas diferentes escalas (atômica, molecular e macromolecular), estando relacionada às diversas áreas do conhecimento (engenharia, física, química, biologia, eletrônica, computação, medicina), a nanotecnologia diz respeito à produção, caracterização e aplicação dos nanomateriais nas mais diferentes áreas.4,5 Sendo assim, nanociência e nanotecnologia objetivam a compreensão, o controle e aplicação da matéria na escala nanométric

Interaction of chitosan and mucin in a biomembrane model environment

AbstractChitosans have been widely exploited in biological applications, including drug delivery and tissue engineering, especially owing to their mucoadhesive properties, but the molecular-level mechanisms for the chitosan action are not known in detail. It is believed that chitosan could affect the mucus by interacting with the proteins mucins, in a process mediated by the cell membrane. In this study we used Langmuir monolayers of dimyristoylphosphatidic acid (DMPA) as simplified membrane models to investigate the interplay between the activity of mucins and chitosan. Surface pressure and surface potential measurements were performed with DMPA monolayers onto which chitosan and/or mucin was adsorbed. We found that the expanding effect from mucin was considerably reduced when chitosan was injected after mucin had been adsorbed on the DMPA monolayer. The results were consistent with the formation of complexes between mucin and chitosan, thus highlighting the importance of electrostatic interactions. Furthermore, chitosan could remove mucin that was co-deposited along with DMPA in Langmuir–Blodgett (LB) films, which could be ascribed to molecular-level interactions between chitosan and mucin inferred from the FTIR spectra of the LB films. In conclusion, the results with Langmuir and LB films suggest that electrostatic interactions are crucial for the mucoadhesive mechanism, which is affected by the complexation between chitosan and mucin

Electronic Tongue Based on Nanostructured Hybrid Films of Gold Nanoparticles and Phthalocyanines for Milk Analysis

The use of gold nanoparticles combined with other organic and inorganic materials for designing nanostructured films has demonstrated their versatility for various applications, including optoelectronic devices and chemical sensors. In this study, we reported the synthesis and characterization of gold nanoparticles stabilized with poly(allylamine hydrochloride) (Au@PAH NPs), as well as the capability of this material to form multilayer Layer-by-Layer (LbL) nanostructured films with metal tetrasulfonated phthalocyanines (MTsPc). Film growth was monitored by UV-Vis absorption spectroscopy, atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). Once LbL films have been applied as active layers in chemical sensors, Au@PAH/MTsPc and PAH/MTsPc LbL films were used in an electronic tongue system for milk analysis regarding fat content. The capacitance data were treated using Principal Component Analysis (PCA), revealing the role played by the gold nanoparticles on the LbL films electrical properties, enabling this kind of system to be used for analyzing complex matrices such as milk without any prior pretreatment

Biomimetic biosensor based on lipidic layers containing tyrosinase and lutetium bisphthalocyanine for the detection of antioxidants

This paper describes the preparation of a biomimetic Langmuir-Blodgett film of tyrosinase incorporated in a lipidic layer and the use of lutetium bisphthalocyanine as an electron mediator for the voltammetric detection of phenol derivatives, which include one monophenol (vanillic acid), two diphenols (catechol and caffeic acid) and two triphenols (gallic acid and pyrogallol). The first redox process of the voltammetric responses is associated with the reduction of the enzymatically formed o-quinone and is favoured by the lutetium bisphthalocyanine because significant signal amplification is observed, while the second is associated with the electrochemical oxidation of the antioxidant and occurs at lower potentials in the presence of an electron mediator. The biosensor shows low detection limit (1.98 × 10-6 - 27.49 × 10-6 M), good reproducibility, and high affinity to antioxidants (KM in the range of 62.31-144.87 μM).\ud The excellent functionality of the enzyme obtained using a biomimetic immobilisation method, the selectivity afforded by enzyme catalysis, the signal enhancement caused by the lutetium bisphthalocyanine mediator and the increased selectivity of the curves due to the occurrence of two redox processes make these sensors exceptionally suitable for the detection of phenolic compounds.MICINN (AGL2009-12660/ALI)FAPESPCNPqCAPE

Enzymes immobilized in Langmuir-Blodgett films: Why determining the surface properties in Langmuir monolayer is important?

ABSTRACT In this review we discuss about the immobilization of enzymes in Langmuir-Blodgett films in order to determine the catalytic properties of these biomacromolecules when adsorbed on solid supports. Usually, the conformation of enzymes depends on the environmental conditions imposed to them, including the chemical composition of the matrix, and the morphology and thickness of the film. In this review, we show an outline of manuscripts that report the immobilization of enzymes as LB films since the 1980’s, and also some examples of how the surface properties of the floating monolayer prepared previously to the transfer to the solid support are important to determine the efficiency of the resulting device