A presente dissertação trata da implementação, em um equipamento de eletroforese capilar (CE) com detecção condutométrica sem contato (C4D), de um sistema de controle externo do fluxo eletrosmótico (EOF) via tensão radial externa (Vrad). Através do potencial externo, aplicado diretamente ao capilar, é possível ter o controle do fluxo eletrosmótico de CE, pois, de forma simplificada, esta prática acopla vetorialmente um potencial externo aplicado com o potencial através da solução tampão dentro do capilar. O emprego da técnica possibilitou o aumento de resolução de 2 aminoácidos - Leucina e Isoleucina, cujas mobilidades diferem apenas de 0,12 cm2.V-1.s-1 entre si, em ácido acético 500 mmol.L-1 com pH = 2,55. A estratégia empregada aqui foi a que denominamos de \"coluna capilar infinita\", na qual, com as sucessivas inversões na direção do EOF, conseguimos aprisionar, dentro da coluna capilar, espécies com mobilidade eletroforética menor que a mobilidade do EOF. A literatura descreve que a inversão do EOF se torna mais difícil com o aumento do pH. Foram realizados testes em eletrólitos contendo agentes inversores de fluxo como o CTAB, o CaCl2 e o BaCl2. Ambos os aditivos foram usados em concentrações muito baixas, nas quais foi mantida a direção normal do EOF, sendo que a utilizaçãode tais agentes teve a finalidade apenas de reduzir os grupos silanolatos em soluções de pH acima de 6,0. Tal estratégia proporcionou a reversão do EOF no sistema tampão MES/HIS, cujo pH estava em torno de 6,1. Por fim, a pesquisa gerou uma perspectiva interessante que é a possibilidade de se encontrar combinações de eletrólitos de corrida e surfactantes com o intuito de se estender a faixa de alcance do Vrad para valores altos de pH. / This work presents the implementation, in an equipment for capillary electrophoresis (CE) with contactless conductivity detection (C4D), of a system for external control of the electroosmotic flow (EOF) via external radial voltage (Vrad). Through external potential, directly applied to the capillary, the electroosmotic flow can be controlled, because this practice couples the applied external potential to the zeta potential through the buffer solution within the capillary. The use of the technique allowed the baseline resolution of two amino acids (Leucine and Isoleucine), whose mobilities differ only by 0,12 cm2.V-1.s-1, using acetic acid 500 mmol.L-1 at pH = 2,55 as the running electrolyte. The approach, called \"infinite capillary column\", consists in successive reversals in the direction of the EOF, trapping species within the capillary column with electrophoretic mobility smaller than the EOF mobility. Thus, the two amino acids were retained by a period of approximately 120 minutes in the capillary that was enough to promote the baseline resolution. Previous works describe that the reversion of the EOF becoming more difficult as pH increases. In order to achieve a more effective control of EOF at high pH values (limiting the technique to a narrow performance band), tests were carried out in electrolytes containing flow reversing agents such as CTAB, CaCI2 and BaCI2. These additives were used at very low concentrations, which kept the normal direction of EOF, and the use of such agents had only the purpuse of reducing the density of silanolate groups in solutions of pH above 6,0. This approach allowed the reversion of the EOF using MES/HIS buffer, which pH was 6,1. Finally, this research has generated an interesting perspective about the possibility of finding combinations of electrolytes and surfactants aiming the Vrad range´s extension at high pH values.

A presente dissertação trata da implementação, em um equipamento de eletroforese capilar (CE) com detecção condutométrica sem contato (C4D), de um sistema de controle externo do fluxo eletrosmótico (EOF) via tensão radial externa (Vrad). Através do potencial externo, aplicado diretamente ao capilar, é possível ter o controle do fluxo eletrosmótico de CE, pois, de forma simplificada, esta prática acopla vetorialmente um potencial externo aplicado com o potencial através da solução tampão dentro do capilar. O emprego da técnica possibilitou o aumento de resolução de 2 aminoácidos - Leucina e Isoleucina, cujas mobilidades diferem apenas de 0,12 cm2.V-1.s-1 entre si, em ácido acético 500 mmol.L-1 com pH = 2,55. A estratégia empregada aqui foi a que denominamos de \"coluna capilar infinita\", na qual, com as sucessivas inversões na direção do EOF, conseguimos aprisionar, dentro da coluna capilar, espécies com mobilidade eletroforética menor que a mobilidade do EOF. A literatura descreve que a inversão do EOF se torna mais difícil com o aumento do pH. Foram realizados testes em eletrólitos contendo agentes inversores de fluxo como o CTAB, o CaCl2 e o BaCl2. Ambos os aditivos foram usados em concentrações muito baixas, nas quais foi mantida a direção normal do EOF, sendo que a utilizaçãode tais agentes teve a finalidade apenas de reduzir os grupos silanolatos em soluções de pH acima de 6,0. Tal estratégia proporcionou a reversão do EOF no sistema tampão MES/HIS, cujo pH estava em torno de 6,1. Por fim, a pesquisa gerou uma perspectiva interessante que é a possibilidade de se encontrar combinações de eletrólitos de corrida e surfactantes com o intuito de se estender a faixa de alcance do Vrad para valores altos de pH. / This work presents the implementation, in an equipment for capillary electrophoresis (CE) with contactless conductivity detection (C4D), of a system for external control of the electroosmotic flow (EOF) via external radial voltage (Vrad). Through external potential, directly applied to the capillary, the electroosmotic flow can be controlled, because this practice couples the applied external potential to the zeta potential through the buffer solution within the capillary. The use of the technique allowed the baseline resolution of two amino acids (Leucine and Isoleucine), whose mobilities differ only by 0,12 cm2.V-1.s-1, using acetic acid 500 mmol.L-1 at pH = 2,55 as the running electrolyte. The approach, called \"infinite capillary column\", consists in successive reversals in the direction of the EOF, trapping species within the capillary column with electrophoretic mobility smaller than the EOF mobility. Thus, the two amino acids were retained by a period of approximately 120 minutes in the capillary that was enough to promote the baseline resolution. Previous works describe that the reversion of the EOF becoming more difficult as pH increases. In order to achieve a more effective control of EOF at high pH values (limiting the technique to a narrow performance band), tests were carried out in electrolytes containing flow reversing agents such as CTAB, CaCI2 and BaCI2. These additives were used at very low concentrations, which kept the normal direction of EOF, and the use of such agents had only the purpuse of reducing the density of silanolate groups in solutions of pH above 6,0. This approach allowed the reversion of the EOF using MES/HIS buffer, which pH was 6,1. Finally, this research has generated an interesting perspective about the possibility of finding combinations of electrolytes and surfactants aiming the Vrad range´s extension at high pH values.

No description available.

In this thesis the possibilities of using capillary electrophoresis as a separation technique for analysis of proteins and microbubbles is presented. A complete analytical process consists of five necessary steps of which one is the actual analysis step. For this step a suitable analytical technique is needed. Capillary electrophoresis (CE) is one of the common analytical separation techniques used for analysis of a diversity of analytes, and can be both used in routine analysis and for research purposes. The reason for using CE, compared to other liquid-based separation techniques, is mainly short analysis time, high resolution, and negligible sample volumes and solvent waste. Depending on the characteristics of the analytes, and the sample matrix, different modes of CE can be used, where capillary zone electrophoresis (CZE) is the most employed one. The basic principle of CZE is separation of the analytes due to differences in total mobility, which is dependent on the charge and size of the analytes, and the electroosmotic flow (EOF). The EOF can be controlled by several parameters e.g. choice of background electrolyte (BGE), and the optimization of the parameters has been discussed throughout the thesis. To improve the properties of the BGE, an ethylammonium nitrate (EAN) water solution was used as BGE for CE analysis in Paper I. The precision of the EOF with this method was determined by adjusting the pH of the BGE, the concentration of EAN in the BGE, and the electric field. Model proteins were thereafter analysed using the optimal parameters yielding a precision sufficient for routine control. One example of the applications of CE is separation of novel contrast agents, which consist of polyvinyl alcohol microbubbles (PVA-MBs). In Paper II, a method for analysis of PVA-MBs in biological samples using CE with UV-detection was developed. It was also established that intact PVA-MBs could be distinguished from ultrasound degraded PVA-MBs in the same set-up. / <p>QC 20171012</p>

Em eletroforese capilar, a reprodutibilidade depende essencialmente da manutenção do sinal e no tempo de migração das espécies. A alteração do fluxo eletrosmótico (EOF) entre corridas é um dos principais fatores que afetam esses parâmetros. Nesse trabalho, é proposto um sistema de monitoramento do EOF baseado em marcas térmicas (TMs), que consistem em sinais presentes em um eletroferograma devido a uma perturbação do eletrólito de corrida ocasionada por um breve aquecimento (da ordem de 100 ms) de uma pequena porção do capilar (aproximadamente 1 mm), sob ação do campo elétrico. O dispositivo responsável pelo aquecimento que se mostrou mais eficiente consistiu em um resistor SMD de 15 &#937; sobre o qual 5 V eram aplicados para gerar aquecimento. Estudos sobre a origem das TMs sugerem que o fenômeno está relacionado às mudanças do número de transporte das espécies devido à variação de temperatura. Essas conclusões foram baseadas na comparação do perfil dos sinais de TM com valores de número de transporte, além de estudos envolvendo simulação computacional. Diversas aplicações para as marcas térmicas foram propostas: correção de variação de tempo de migração devido a alterações do EOF, medida direta do EOF e para otimização de parâmetros do detector condutométrico sem contato. As TMs revelaram-se, então, um sistema prático e de fácil implementação, que pode ser utilizado como uma espécie de padrão interno. Adicionalmente, o emprego das TMs em um novo sistema de injeção de amostra, chamado de injeção térmica, foi também proposto. A vantagem desse tipo de injeção consiste na minimização de problemas de contínua introdução de amostra no canal de separação em microchip-CE. Para realizar essa injeção, o capilar é preenchido com a amostra diluída em um eletrólito de corrida e a injeção ocorre quando uma TM é gerada. Estudos com soluções de NaCl apresentaram faixa de resposta linear entre 10 &#181;mol L-1 e 1 mmol L-1 para sódio. Entretanto, problemas de interferência sobre a sensibilidade e a mobilidade dos analitos foram obstáculos enfrentados. Também foi alvo de estudo o emprego da injeção térmica em uma técnica de multiplexação para aumento de relação sinal/ruído, baseado em um novo algoritmo. Embora o modelamento matemático tenha sido eficiente para decodificação de sinais, não foi possível obter o aumento na relação sinal/ruído almejado, pois o tempo de análise seria excessivamente longo. No entanto, a utilização da injeção térmica nesse tipo de estratégia mostrou-se bastante adequada, pois ela requer que diversas injeções sejam realizadas sequencialmente sem a interrupção do potencial de corrida, característica que esse sistema de injeção permite. Posteriormente, a implementação de estratégias que gerassem TMs em tempos mais curtos poderiam viabilizar a técnica. Finalmente, a utilização de TMs como ferramenta para obtenção de constantes físico-químicas, como pKa e mobilidade por exemplo, utilizando a eletroforese capilar mostra-se como uma grande perspectiva para a técnica / In capillary electrophoresis, reproducibility depends essentially on the maintenance of the signal and the migration time when the analysis of the same sample is repeated. Variations in the electroosmotic flow (EOF) between runs are one of the major factors affecting these parameters. In this work, a new approach to monitor the EOF based on thermal marks (TMs) is proposed. TM consists in a signal present in the electropherogram caused by heating (typically 100 ms) a small portion of the capillary (approximately 1 mm), while the electric field is applied. The most effective device to promote the heating was a 15-&#937; SMD resistor, powered at 5 V. Studies about the origin of TMs suggest that the phenomenon is related to variations in the transport number of the species due to alterations in the temperature. This conclusion was based on comparison between the TM profile and the transport numbers values, as well as results from computer simulation. The proposed applications for TM include: correction in variations of migration times with alterations on EOF, EOF measurement and optimization of the parameters of contactless conductivity detection. Additionally, a new sample injection procedure, called thermal injection, was also proposed. The advantage of this injection consists in minimization of leakage problems related to the continuous introduction of the sample in the separation channel in microchip-CE. To perform the thermal injection, the capillary is completely filled with the sample diluted in a BGE and the injection occurs with the generation of a TM. Studies with NaCl solutions presented extensive linear response range from 10 &#181;mol L-1 to 1 mmol L-1. However, interference problems on sensibility and analytes mobilities appeared. The use of low-concentration solutions diminishes these problems. However, the analytical signal is also diminished, needing a strategy to raise the sensitivity. Thus, a multiplexing technique based on a new algorithm was also introduced in order to improve signal-to-noise ratio. Although the efficiency of the mathematic modeling on the signals decoding, the desired improvement of signal/noise ratio was not obtained, because the analysis time would be excessively high. However, the employment of the thermal injection seems to be very suitable for multiplexing, due to the possibility of performing several sequential injections with no interruption of the electric field. Afterwards, the implementation of fast velocity devices to generate TMs would enable the technique. Finally, the great perspective to applications of TM concerns in the use of TMs to obtain physical chemical constants, such as pKa and ionic mobilities. The present work describes values of ionic mobilities calculated to monopropyl carbonate, monoisopropyl carbonate, and hydronium.

Em eletroforese capilar, a reprodutibilidade depende essencialmente da manutenção do sinal e no tempo de migração das espécies. A alteração do fluxo eletrosmótico (EOF) entre corridas é um dos principais fatores que afetam esses parâmetros. Nesse trabalho, é proposto um sistema de monitoramento do EOF baseado em marcas térmicas (TMs), que consistem em sinais presentes em um eletroferograma devido a uma perturbação do eletrólito de corrida ocasionada por um breve aquecimento (da ordem de 100 ms) de uma pequena porção do capilar (aproximadamente 1 mm), sob ação do campo elétrico. O dispositivo responsável pelo aquecimento que se mostrou mais eficiente consistiu em um resistor SMD de 15 &#937; sobre o qual 5 V eram aplicados para gerar aquecimento. Estudos sobre a origem das TMs sugerem que o fenômeno está relacionado às mudanças do número de transporte das espécies devido à variação de temperatura. Essas conclusões foram baseadas na comparação do perfil dos sinais de TM com valores de número de transporte, além de estudos envolvendo simulação computacional. Diversas aplicações para as marcas térmicas foram propostas: correção de variação de tempo de migração devido a alterações do EOF, medida direta do EOF e para otimização de parâmetros do detector condutométrico sem contato. As TMs revelaram-se, então, um sistema prático e de fácil implementação, que pode ser utilizado como uma espécie de padrão interno. Adicionalmente, o emprego das TMs em um novo sistema de injeção de amostra, chamado de injeção térmica, foi também proposto. A vantagem desse tipo de injeção consiste na minimização de problemas de contínua introdução de amostra no canal de separação em microchip-CE. Para realizar essa injeção, o capilar é preenchido com a amostra diluída em um eletrólito de corrida e a injeção ocorre quando uma TM é gerada. Estudos com soluções de NaCl apresentaram faixa de resposta linear entre 10 &#181;mol L-1 e 1 mmol L-1 para sódio. Entretanto, problemas de interferência sobre a sensibilidade e a mobilidade dos analitos foram obstáculos enfrentados. Também foi alvo de estudo o emprego da injeção térmica em uma técnica de multiplexação para aumento de relação sinal/ruído, baseado em um novo algoritmo. Embora o modelamento matemático tenha sido eficiente para decodificação de sinais, não foi possível obter o aumento na relação sinal/ruído almejado, pois o tempo de análise seria excessivamente longo. No entanto, a utilização da injeção térmica nesse tipo de estratégia mostrou-se bastante adequada, pois ela requer que diversas injeções sejam realizadas sequencialmente sem a interrupção do potencial de corrida, característica que esse sistema de injeção permite. Posteriormente, a implementação de estratégias que gerassem TMs em tempos mais curtos poderiam viabilizar a técnica. Finalmente, a utilização de TMs como ferramenta para obtenção de constantes físico-químicas, como pKa e mobilidade por exemplo, utilizando a eletroforese capilar mostra-se como uma grande perspectiva para a técnica / In capillary electrophoresis, reproducibility depends essentially on the maintenance of the signal and the migration time when the analysis of the same sample is repeated. Variations in the electroosmotic flow (EOF) between runs are one of the major factors affecting these parameters. In this work, a new approach to monitor the EOF based on thermal marks (TMs) is proposed. TM consists in a signal present in the electropherogram caused by heating (typically 100 ms) a small portion of the capillary (approximately 1 mm), while the electric field is applied. The most effective device to promote the heating was a 15-&#937; SMD resistor, powered at 5 V. Studies about the origin of TMs suggest that the phenomenon is related to variations in the transport number of the species due to alterations in the temperature. This conclusion was based on comparison between the TM profile and the transport numbers values, as well as results from computer simulation. The proposed applications for TM include: correction in variations of migration times with alterations on EOF, EOF measurement and optimization of the parameters of contactless conductivity detection. Additionally, a new sample injection procedure, called thermal injection, was also proposed. The advantage of this injection consists in minimization of leakage problems related to the continuous introduction of the sample in the separation channel in microchip-CE. To perform the thermal injection, the capillary is completely filled with the sample diluted in a BGE and the injection occurs with the generation of a TM. Studies with NaCl solutions presented extensive linear response range from 10 &#181;mol L-1 to 1 mmol L-1. However, interference problems on sensibility and analytes mobilities appeared. The use of low-concentration solutions diminishes these problems. However, the analytical signal is also diminished, needing a strategy to raise the sensitivity. Thus, a multiplexing technique based on a new algorithm was also introduced in order to improve signal-to-noise ratio. Although the efficiency of the mathematic modeling on the signals decoding, the desired improvement of signal/noise ratio was not obtained, because the analysis time would be excessively high. However, the employment of the thermal injection seems to be very suitable for multiplexing, due to the possibility of performing several sequential injections with no interruption of the electric field. Afterwards, the implementation of fast velocity devices to generate TMs would enable the technique. Finally, the great perspective to applications of TM concerns in the use of TMs to obtain physical chemical constants, such as pKa and ionic mobilities. The present work describes values of ionic mobilities calculated to monopropyl carbonate, monoisopropyl carbonate, and hydronium.

No description available.

Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signalto-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently iv proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the v planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.