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Novas tecnologias para fabricação de microsistemas analíticos e detecção eletroquímica; New technologies for the fabrication of microluidic devices with electrochemical detection

Piccin, Evandro
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 11/04/2008 PT
Relevância na Pesquisa
172.538%
Este trabalho de doutorado apresenta o desenvolvimento de novas tecnologias para fabricação de microsistemas analíticos e detecção eletroquímica. Primeiramente, a poliuretana elastomérica, derivada de uma fonte renovável, o óleo de mamona, foi utilizada como um novo e alternativo material para fabricação de microdispositivos. Foram avaliadas as características físicas dos microcanais formados por moldagem, a compatibilidade química com solventes e eletrólitos, as características de superfície através dos ângulos de contato, o EOF em diferentes pHs e a performance analítica em experimentos de eletroforese com detecção eletroquímica. A segunda parte do trabalho apresenta o desenvolvimento de um método para a determinação simultânea de azo-corantes comumente usados na indústria alimentícia. Amaranto, amarelo crepúsculo FCF, amarelo sólido AB, ponceu 4R e vermelho 2G, foram separados e quantificados através de eletroforese em microdispositivos com detecção eletroquímica. Foram estudados e otimizados vários parâmetros que influenciaram a separação eletroforética e detecção eletroquímica, em experimentos realizados usando microdispositivos de vidro e eletrodo de trabalho de carbono vítreo. Finalmente...

Derivatização eletroquímica da álcoois num sistema em fluxo para determinação quantitativa por eletroforese capilar com detecção condutométrica sem contato; Electrochemical derivatization of alcohols in a flow system for quantitative determinations by capillary electrophoresis and contactless conductivity detection

Santos, Mauro Sergio Ferreira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/10/2012 PT
Relevância na Pesquisa
172.538%
A eletroforese capilar (CE) é uma técnica poderosa de separação que explora as diferenças na mobilidade de espécies iônicas sob efeito do campo elétrico. Não permite, contudo, separação de misturas de moléculas neutras, possível mediante formação de complexos com carga, derivatização química ou cromatografia eletrocinética micelar (MEKC). A derivatização eletroquímica tem sido usada em combinação com HPLC, entre outras técnicas, mas não ainda com CE e para fins quantitativos, como proposto e demonstrado nesta dissertação, em que se enfoca, como sistemas modelo, álcoois primários de cadeia curta e se recorre a sistema em fluxo designado de EC-CE-C4D, que consiste de uma célula eletroquímica acoplada com equipamento de eletroforese capilar provido de detector de condutividade sem contato direto com os eletrodos. O sistema EC-CE-C4D, inicialmente concebido para efetuar pré-concentração e redissolução eletroquímica de metais seguida de separação eletroforética, possibilitou também o monitoramento de produtos com carga, formados em processos eletrocatalíticos, fato que inspirou a investigação da aplicabilidade, também do sistema à derivatização eletroquímica de analitos neutros em iônicos ou ionizáveis. Inicialmente...

Sensing cooperativity in ATP hydrolysis for single multisubunit enzymes in solution

Jiang, Yan; Douglas, Nicholai R.; Conley, Nicholas R.; Miller, Erik J.; Frydman, Judith; Moerner, W. E.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
179.1334%
In order to operate in a coordinated fashion, multisubunit enzymes use cooperative interactions intrinsic to their enzymatic cycle, but this process remains poorly understood. Accordingly, ATP number distributions in various hydrolyzed states have been obtained for single copies of the mammalian double-ring multisubunit chaperonin TRiC/CCT in free solution using the emission from chaperonin-bound fluorescent nucleotides and closed-loop feedback trapping provided by an Anti-Brownian ELectrokinetic trap. Observations of the 16-subunit complexes as ADP molecules are dissociating shows a peak in the bound ADP number distribution at 8 ADP, whose height falls over time with little shift in the position of the peak, indicating a highly cooperative ADP release process which would be difficult to observe by ensemble-averaged methods. When AlFx is added to produce ATP hydrolysis transition state mimics (ADP·AlFx) locked to the complex, the peak at 8 nucleotides dominates for all but the lowest incubation concentrations. Although ensemble averages of the single-molecule data show agreement with standard cooperativity models, surprisingly, the observed number distributions depart from standard models, illustrating the value of these single-molecule observations in constraining the mechanism of cooperativity. While a complete alternative microscopic model cannot be defined at present...

Permeability studies in biomimetic glycosaminoglycan-hydrogel membranes

Mattern, Kristin J. (Kristin Julie)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 280 p.
ENG
Relevância na Pesquisa
198.43379%
The rates of water and solute transport tend to be lower in fibrous materials than in bulk solution. This phenomenon of "hindered transport" is caused by steric, hydrodynamic, and electrostatic interactions between the solvent, the solute, and the fibers. In this research the effect of these interactions were studied using charged, fibrous agarose-glycosaminoglycan (GAG) membranes. The work was motivated by current research into the role of the glomerular capillary wall (GCW) in ultrafiltering blood plasma, which is the first step in the processing of blood by the kidney. The GCW is composed of three layers in series: an endothelium, a basement membrane, and an epithelium. Intreasing evidence from experimental results and theoretical models of the GCW indicate that the endothelial layer and its associated glycocalyx may significantly limit the transport of macromolecules across the glomerular barrier. The glycocalyx is primarily composed of proteoglycans, a fibrous mixtures of proteins and anionic GAG. GAG fibers are present in many other biological materials, such as basement membranes and cartilage, making the current studies in agarose-GAG relevant to a variety of biological systems. Agarose-GAG membranes were synthesized by using 1-cyano-4-(dimethylamino)pyridinium tetrafluoroborate (CDAP) to create reactive sites in thin agarose hydrogels. Chondroitin sulfate GAG was then covalently bound to the reactive sites via their terminal amine group. By manipulating the temperature and duration of key reaction steps...

Induced-charge electrokinetics at large voltages

Kilic, Mustafa Sabri
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 173 p.
ENG
Relevância na Pesquisa
179.1334%
The classical transport theory cannot explain the experimental behavior of electrochemical systems in the extreme operating conditions required by modern microfluidics devices. Some experimental puzzles include strange behavior of colloidal particles, high-frequency flow reversal in microfluidic ACEO pumps, and concentration dependence of electrokinetic slip. Theoretical developments would help not only in exploiting poorly understood effects favorably, but also in building more efficient microfluidics devices. The goal of this thesis is to explore possible mechanisms and modifications of the current theory that would enable us to interpret the experimental data. The following is a brief summary of the contributions of this thesis to the subject: Colloidal Particles. A new invention in colloidal science is the Janus particle, which is a two-faced spherical particle where one face is polarizable, and the other non-polarizable. These particles have potential applications in drug delivery, building of nanowires and solar energy. Experiments show that Janus particles strongly interact with boundaries: they approach walls, swim along walls, or sometimes jump away from walls. We show, by conducting numerical simulations of this truly 3D problem...

Impact of electroviscosity on the hydraulic conductance of the bordered pit membrane: a theoretical investigation

Santiago, M.; Pagay, V.; Stroock, A.D.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
297.34361%
In perfusion experiments, the hydraulic conductance of stem segments ( ) responds to changes in the properties of the perfusate, such as the ionic strength ( ), pH, and cationic identity. We review the experimental and theoretical work on this phenomenon. We then proceed to explore the hypothesis that electrokinetic effects in the bordered pit membrane (BPM) contribute to this response. In particular, we develop a model based on electroviscosity in which hydraulic conductance of an electrically charged porous membrane varies with the properties of the electrolyte. We use standard electrokinetic theory, coupled with measurements of electrokinetic properties of plant materials from the literature, to determine how the conductance of BPMs, and therefore , may change due to electroviscosity. We predict a nonmonotonic variation of with with a maximum reduction of 18%. We explore how this reduction depends on the characteristics of the sap and features of the BPM, such as pore size, density of chargeable sites, and their dissociation constant. Our predictions are consistent with changes in observed for physiological values of sap and pH. We conclude that electroviscosity is likely responsible, at least partially, for the electrolyte dependence of conductance through pits and that electroviscosity may be strong enough to play an important role in other transport processes in xylem. We conclude by proposing experiments to differentiate the impact of electroviscosity on from that of other proposed mechanisms.; Michael Santiago...

General electrokinetic model for concentrated suspensions in aqueous electrolyte solutions: electrophoretic mobility and electrical conductivity in static electric fields

Carrique Fern??ndez, F??lix; Ruiz-Reina, Emilio; Roa, Rafael; Arroyo Rold??n, Francisco J.; Delgado, ??ngel V.
Fonte: Elsevier Publicador: Elsevier
Tipo: Pré-impressão
ENG
Relevância na Pesquisa
935.9225%
In recent years different electrokinetic cell models for concentrated colloidal suspensions in aqueous electrolyte solutions have been developed. They share some of its premises with the standard electrokinetic model for dilute colloidal suspensions, in particular, neglecting both the specific role of the so-called added counterions (i.e., those released by the particles to the solution as they get charged), and the realistic chemistry of the aqueous solution on such electrokinetic phenomena as electrophoresis and electrical conductivity. These assumptions, while having been accepted for dilute conditions (volume fractions of solids well below 1 %, say), are now questioned when dealing with concentrated suspensions. In this work, we present a general electrokinetic cell model for such kind of systems, including the mentioned effects, and we also carry out a comparative study with the standard treatment (the standard solution only contains the ions that one purposely adds, without ionic contributions from particle charging or water chemistry). We also consider an intermediate model that neglects the realistic aqueous chemistry of the solution but accounts for the correct contribution of the added counterions. The results show the limits of applicability of the classical assumptions and allow one to better understand the relative role of the added counterions and ions stemming from the electrolyte in a realistic aqueous solution...

Transport in polymer-gel composites: Theoretical methodology and response to an electric field

Hill, Reghan J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
379.13258%
A theoretical model of electromigrative, diffusive and convectivetransport polymer-gel composites is presented. Bulk properties are derived from the standard electrokinetic model with an impenetrable charged sphere embedded in an electrolyte-saturated Brinkman medium. Because the microstructure can be carefully controlled, these materials are promising candidates for enhanced gel-electrophoresis, chemical sensing, drug delivery, and microfluidic pumping technologies. The methodology provides `exact' solutions for situations where perturbations from equilibrium are induced by gradients of electrostatic potential, concentration and pressure. While the volume fraction of the inclusions should be small, Maxwell's well-known theory of conduction suggests that the theory may also be accurate at moderate volume fractions. In this work, the model is used to compute ion fluxes, electrical current density, and convective flow induced by an applied electric field. The electric-field-induced (electro-osmotic) flow is a sensitive indicator of the inclusion zeta-potential and size, electrolyte concentration, and Darcy permeability of the gel, while the electrical conductivity increment is most often independent of the polymer gel, and is much less sensitive to particle and electrolyte characteristics.

`Exact' solutions of the full electrokinetic model for soft spherical colloids: Electrophoretic mobility

Hill, Reghan J.; Saville, D. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/05/2005
Relevância na Pesquisa
612.20805%
Numerical solutions of the standard electrokinetic model provide a basis for interpreting a variety of electrokinetic phenomena involving `bare' colloids. However, the model rests on the classical notion of a shear or slipping plane, whose location is unknown when surfaces are coated with permeable polymer. Consequently, an electrokinetic model for `soft', `hairy' or `fuzzy' colloids has been developed, but until recently solutions were available only for several restricted cases, most notably for particles with thin, uniform layers, and without polarization and relaxation. Here we present numerically exact solutions of the full model for a variety of soft colloids, including PEG-coated liposomes, PEO-coated latices, human erythrocytes, and polyelectrolyte micelles. Particular attention is given to linking the thickness, density and permeability of the coatings, which are key parameters in the model, to ``physical'' quantities, such as the polymer molecular weight, adsorbed amount, and hydrodynamic layer thickness. This paper also identifies limits--on the ionic strength, particle size, layer thickness and permeability--beyond which earlier theories breakdown. In short, polarization and relaxation are as influential on the mobility of soft colloids as they are for `bare' particles.