Name: dynamic electrochemical measurement of chloride ions
Uploaded: 2016-02-05T13:00:00.000+00:00
Duration: 7 min 32 s
Description: Watch this Scientific Journal Video about Dynamic Electrochemical Measurement of Chloride Ions at JoVE.com

This work is a part of the STW project "Integral solution for sustainable construction (IS2C, Fleur van Rossem for her support during the chip fabrication, Justyna Wiedemair for the chip design and Allison Bidulock for her support during the manuscript preparation.

1. fabricação de chips Nota: O chip é constituído por um eléctrodo de Ag / AgCl de trabalho (WE), um eléctrodo de pseudo-referência de Ag / AgCl (RE-pseudo) e um contra-eléctrodo de platina sobre um chip de vidro. O metal de prata é depositado sobre um chip de vidro, utilizando os processos de 16 sala limpa padrão. Em seguida, é chloridized em M FeCl3 solução de 0,1 durante 30 segundos para formar uma camada de AgCl sobre a superfície. O Ag / AgCl WE (área = 9,812 milímetros 2) está localizada no centro, rodeado pela pseudo-RE Ag / AgCl, como mostrado na Figura 1. <ol><li> Depositar o metal de prata no vidro para formar um eléctrodo de prata planar. O chip de fabrico passo-a-passo para uma sala limpa é dada como se segue: <ol><li> Litografia <ol><li> Para a limpeza wafer, mergulhe a pastilha de vidro pela primeira vez em conc. HNO 3 banho para remover qualquer contaminação orgânica e, em seguida, em 1 M de KOH para limpar a superfície. </li><li> Aplicar uma foto positiva resistir (200 nm de espessura) aobolacha por revestimento rotativo e o pré-cozimento resistir a 95 ° C durante 15 min. </li><li> Expor a bolacha à luz UV durante 5 segundos através de uma máscara de vidro. </li><li> Desenvolver o fotorresiste em solução desenvolvedor. Isto irá expor a área de eléctrodos de vidro onde será depositado e a área restante será coberto pela resistir não exposta. </li></ol></li><li> glass Etching <ol><li> Imergir a bolacha de vidro desenvolvido no banho de KOH para gravar a área exposta do vidro. </li></ol></li><li> Metal Deposition (Sputtering) <ol><li> metal prateado depósito na área de vidro exposta. <ol><li> Em primeiro lugar de depósito de uma camada de 20 nm de titânio (Ti) (por pulverização), como uma camada de adesão de vidro. </li><li> Em seguida, deposita camada de 70 nm de paládio (Pd) (por pulverização), como uma barreira de difusão entre a prata e Ti. </li><li> Finalmente depositar 500 nm de metal prateado. Esta é a espessura do metal depositado. A área do eléctrodo de trabalho é de 4 mm2. </li><li> Remover o remaining resistir pelo processo de lift-off em um banho de acetona. </li></ol></li><li> Dado o hóstia no tamanho único chip. O chip está agora pronto para ser chloridized para formar um eléctrodo de Ag / AgCl no chip. </li></ol></li></ol></li><li> Colocar o chip num suporte de chip de politetrafluoroetileno concebido em casa, como mostrado na Figura 1. O suporte proporciona ligações eléctricas fácil através de os pinos (ou pinos carregados por mola) e contém uma célula electroquímica. </li><li> Chloridize o eléctrodo de prata para formar um eléctrodo de Ag / AgCl sobre o chip. Para isso, derrame H FeCl solução 0,1 3 na célula durante 30 seg. ou até que a cor de prata do eletrodo torna-se cinzento escuro. imersão já não é crítico enquanto que mais curto tempo de imersão pode conduzir a não deposição de Ag / AgCl. </li><li> Enxaguar o chip com água desionizada para limpar o restante chip de FeCl 3 .O está agora pronto para ser utilizado para a medição cronopotenciometria. </li></ol>2. Preparação de eletrólitos Nota: Os electrólitos foram preparadas com diferentes concentrações de cloreto de potássio em 0,5 M de KNO 3. <ol><li> Preparar 50 ml de 50 mM de KCl solução de electrólito (0,186 g de KCl em 50 ml de solução). </li><li> Na mesma solução adicionar 2,52 g de KNO 3 para formar um KNO 3 0,5 M fundo electrólito. </li><li> Manter a concentração inicial de cloreto de zero e KNO 3-0,5 M. Em outras palavras adicionar 2,52 g de KNO 3 em 50 ml de água desionizada. </li><li> Adicionar 50 mM de KCl para aumentar a concentração de ião cloreto (de 1 mm a 6 mm) de electrólito, sistematicamente, como mostrado nos passos seguintes. <ol><li> Adicionar 100 ul de cloreto de potássio 50 mM em 4,9 ml de uma 0,5 M KNO 3 para obter 1 mM [Cl]. </li><li> Adicionar 104 ul da solução de 50 mM de KCl para a solução do passo 2.4.1 para obter 2 mM [Cl]. </li><li> Adicionar 108.41 ul de uma solução a 50 mM de KCl para a solução da etapa 2.4.2 para obter 3 mM [CL]. </li><li> Adicionar 113.19 ul de uma solução a 50 mM de KCl para a solução do passo 2.4.3 para obter 4 mM [Cl]. </li><li> Adicionar 118,2 mL de uma solução a 50 mM de KCl para a solução do passo 2.4.4 para obter 5 mM [Cl]. </li><li> Adicionar 123,3 mL de uma solução a 50 mM de KCl para a solução do passo 2.4.5 para obter 6 mM [Cl]. </li></ol></li></ol> 3. Configuração Experimental Nota: As medições foram realizadas usando um potenciostato (Biologic Ciência Instruments, França). <ol><li> Coloque o chip no suporte de chip e ligar o terminal correspondente do potenciostato. </li><li> Ligar o terminal de eléctrodo de trabalho do potenciostato para o eléctrodo de Ag / AgCl. </li><li> Ligar o terminal de eléctrodo de referência do potenciostato para outro eléctrodo de Ag / AgCl. </li><li> Ligar o terminal de eléctrodo contador do potenciostato para o eléctrodo de platina. </li><li> Coloque o compconfiguração da experiência lete em uma gaiola de Faraday para evitar o ruído ambiente. </li></ol> 4. Configurações operacionais Instrumento Nota: Os parâmetros de funcionamento da célula electroquímica é controlado através da interface do utilizador do potenciostato. A resposta do potencial de Ag / AgCl NÓS durante um impulso de corrente aplicada é medido para diferentes concentrações de ião cloreto. <ol><li> No programa potenciostato, abra o cronopotenciometria técnica e definir os parâmetros operacionais. <ol><li> Defina o seguinte parâmetro de acordo com os requisitos: <ol><li> Corrente (I s) </li><li> Tempo de corrente aplicada (s t) </li></ol></li><li> Comece esta técnica, clicando no botão play no programa potenciostato. Nota: O programa potenciostato mostra a resposta potencial como uma função do tempo, sob o impulso de corrente aplicada. </li></ol></li></ol> 5. Medições e Dados Analysis <ol><li> Desenhe a curva de calibração do tempo de transição vs. concentração de iões de Cl no eletrólito. <ol><li> Alterar a concentração de Cl no eletrólito KCl, sistematicamente. <ol><li> Inicie a medição com 5 mL de KCl 1 mM com KNO 3 0,5 M fundo electrólito na célula electroquímica. </li><li> Iniciar a experiência cronopotenciometria usando o potenciostato e aplicar uma corrente de 10 mA / cm2 durante 10 seg e armazenar os dados. </li><li> Sistematicamente alterar a concentração a 6 mm, com incrementos de 1 mm e repetir as medições. </li></ol></li><li> Armazenar os dados medidos como a.mpt arquivo e analisar o arquivo de dados no programa de processamento de dados. <ol><li> Analisar os dados utilizando um programa de processamento de dados desenvolvido internamente para calcular o primeiro derivativo da resposta de potencial e calcular o pico da primeira derivada. O pico da primeira derivada é o momento de transição. Nota: O bacalhau completaing do programa de processamento de dados é dada na informação suplementar de Abbas et al., 2014. </li></ol></li><li> Repetir a medição três vezes com intervalos de 1 hora cada. </li><li> Abrir todos os ficheiros de dados no programa de processamento de dados e calcular o tempo de transição para cada medição. etapas detalhe de cálculo do tempo de transição é dada abaixo: <ol><li> Traça-se a diferença de potencial em função do tempo obtida a partir dos arquivos de dados de medição cronopotenciometria. </li><li> Calcula-se a primeira derivada da resposta de potencial. </li><li> Indicar o máximo da primeira derivada e a hora do evento. O tempo do máximo da derivada de primeira é o tempo de transição. </li></ol></li><li> Para a curva de calibração, traçar a raiz quadrada do tempo de transição em relação à concentração de iões Cl. </li><li> Junto os dados medidos traçar a curva teórica com base na equação de areia 25. Calcule volta o coeffic difusãotário da trama de dados. <ol><li> Na trama de dados medidos entre o tempo de transição e do [CL] tomar qualquer ponto na linha e registrar o valor de tempo de transição e do [CL]. A equação da areia é dada como: τ = (FC * / 2J (1-t Cl -)) 2 Dπ Aqui, C * é a concentração de grandes quantidades de iões Cl, F é a constante de Faraday, j é a densidade de corrente, t Cl - é o número de transportes e D é o coeficiente de difusão. Negligenciar o t Cl -, uma vez que se aproxima de zero para uma maior concentração de eletrólitos fundo. </li><li> A variável único remanescente na equação de areia no coeficiente de difusão; colocar o valor de tempo de transição, a concentração de iões de cloreto e a corrente aplicada na equação Areia obter o valor do coeficiente de difusão. </li></ol></li></ol></li><li> Medição de deriva <ol><li> Pour 5 mL de 1 mM de cloreto de potássio nacélula electroquímica. </li><li> No potenciostato, defina a aplicada atual para ser 10:00 -2 e tempo para ser 10 seg. </li><li> Medir a resposta potencial para 2 semanas com três medição de cada dia com um intervalo de 3 horas entre as medições. </li><li> Recarregar o electrólito, isto é, KCl 1 mM, todos os dias antes da realização das medições. </li><li> Traçar o tempo de transição ao longo de duas semanas de medições. A mudança no tempo de transição, por dia é o desvio da resposta de tempo de transição. </li></ol></li><li> Efeito do eléctrodo de pseudo-referência sobre as medições do tempo de transição Nota: Várias referências pseudo tal como um fio de Ag / AgCl, um fio de platina e um fio de aço são testadas para medir o tempo de transição. <ol><li> Pour 4 mM de KCl electrólito na célula electroquímica. </li><li> Use Ag / AgCl como um eléctrodo de pseudo-referência e conecte-o ao terminal do eletrodo de referência do potenciostato. Devido ao impulso de corrente anódica a Cl &amp; #713; iões estão esgotados perto do eléctrodo de trabalho de Ag / AgCl. </li><li> Realizar a medição cronopotenciometria, aplicando uma densidade de corrente de 15 Am -2 durante 10 seg. </li><li> Repita as medições com platina como eletrodo de pseudo-referência e registrar os dados. </li><li> Repita as medições com barra de aço como um eléctrodo de pseudo-referência e registrar os dados. </li><li> Traçar o tempo de transição medida para vários eletrodos pseudo-referência utilizados. </li><li> Repita o conjunto completo de medição com 5 mM de KCl e traçar o tempo de transição usando vários eletrodos pseudo-referência. </li></ol></li></ol>

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The authors have nothing to disclose.

O tempo de transição é o momento de inflexão; é teoricamente independente da isto é, potencial de referência, o eléctrodo de referência. Por conseguinte, qualquer fio metálico pode ser utilizado como um eléctrodo de pseudo-referência para medições de tempo de transição. Em contraste com a medição potenciométrica existente de iões cloreto no betão este método permite que a longo prazo e calibração da medição livre. Além disso, a sensibilidade e a gama de detecção de concentr...

Um sensor de iões cloreto com base na medição do tempo de transição de um eléctrodo de Ag / AgCl é apresentada. O objectivo é evitar os desvios inerentes durante a monitorização em contínuo a longo prazo dos iões de cloreto no electrólito. medição cronopotenciometria, que é uma abordagem dinâmica de medição, de um eléctrodo de Ag / AgCl é utilizado para esta finalidade. Aqui, uma taxa de variação do potencial de um eléctrodo de Ag / AgCl é medida durante um estímulo (pulso galvanostático). A vantagem desta abordagem é demonstrada por evitar o eléctrodo de referência líquida de junção e, em vez de usar qualquer fio de metal como um eléctrodo de pseudo-referência, portanto, permitindo a detecção de Cl concentração de iões para a longo prazo (anos) e em aplicações in situ, tal como medição dentro de estruturas de concreto. Os iões cloreto em estruturas de betão é uma das principais causas de degradação 1,2. Ele inicia corrosão localizada no reforço de aço and resultados na falha final da estrutura 3. Portanto, medir iões Cl no concreto é inevitável para prever o ciclo de vida de serviço e manutenção de um 4,5 estrutura. Princípios de Detecção diferentes foram relatados para a medição de iões de cloreto no concreto, como eletroquímica 6,7, 8,9 e óptica eletromagnética 10,11. No entanto, métodos ópticos e eletromagnéticos têm configurações volumosos, são difíceis de integrar como um sistema stand-alone e têm problemas com seletividade 12. Na técnica electroquímica, medição potenciométrica de um eléctrodo de Ag / AgCl é o estado da arte 6,7,13 abordagem. Apesar dos resultados promissores, esta abordagem é limitada a medição em escala de laboratório uma vez que os desvios no potencial de referência e de difusão de resultados potenciais de queda em dados falhos 14,15. Uma abordagem tempo de transição com base na medição electroquímica dinâmico (DEM) pode aliviar o problema devido ao potencialderiva 16. No DEM, a resposta do sistema a um estímulo aplicado é medido 17-19. O exemplo de um tal sistema é cronopotenciometria. Aqui, um impulso de corrente aplicada é utilizada como um estímulo esgotar iões perto da superfície do eléctrodo e o potencial de resposta correspondente é medida. Uma corrente anódica a um eléctrodo de Ag / AgCl inicia uma reacção faradaica (Ag + Cl <img alt="figura 1" src="/files/ftp_upload/53312/arrow.jpg" /> AgCl + E), resultando em uma depleção de íons Cl perto da superfície do eletrodo. O potencial alteração é uma função da corrente aplicada e a concentração dos iões (selectivos) do electrólito 12,20. No momento em que estes íons esgotar completamente perto do eletrodo de superfície a taxa de mudança de potenciais aumenta rapidamente, dando um ponto de inflexão 21. O ponto de inflexão sobre a curva de resposta em tempo potencial (chronopotentiogram) mostra o tempo de transição e pode ser determinada a partir damáximo da primeira derivação do potencial de resposta 22. O tempo de transição é uma característica da concentração iónica. Esta abordagem tem sido usada para determinar a concentração diferentes iões 17 e o pH de electrólitos 23,24. No caso de um eléctrodo de Ag / AgCl como um eléctrodo de trabalho (em que a corrente é aplicada) os iões esgotam será iões cloreto 17. Portanto medir o seu tempo de transição irá determinar a sua concentração.

<table><tbody><tr><td>Platinum wire (&amp;ge;99.99% trace metals)</td><td>Sigma Aldrich, the Netherlands</td><td>EP1330-1EA</td><td></td></tr><tr><td>Potassium chloride (BioXtra, &amp;ge;99.0%)</td><td>Sigma Aldrich, the Netherlands</td><td>P9333-500G</td><td></td></tr><tr><td>Potassium hydroxide (90% pure reagent grade)</td><td>Sigma Aldrich, the Netherlands</td><td>484016-1KG</td><td></td></tr><tr><td>Ferric chloride&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td>451649-1G</td><td></td></tr><tr><td>potassium nitrate (&gt;99% reagent grade)&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td>P6083-500G</td><td></td></tr><tr><td>Ag/AgCl liquid junction reference electrode&amp;nbsp;</td><td>BASi, USA</td><td>model MF-2079</td><td></td></tr><tr><td>VSP potentiostat</td><td>Biologic Science Instruments, France</td><td>VSP 300</td><td></td></tr><tr><td>Steel wire</td><td>Microlab TU Delft</td><td></td><td></td></tr><tr><td>Silver wire&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td></td><td></td></tr></tbody></table>

dynamic electrochemical measurement of chloride ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

O eléctrodo de Ag / AgCl é fabricado num chip de vidro (Figura 1) usando um processo padrão de salas limpas. A configuração de medição cronopotenciometria (Figura 2) foi usada e a resposta foi medida usando um potenciostato. Para observar o efeito da concentração de iões Cl no tempo de transição, soluções contendo 4, 5 e 6 mM de Cl íons em uma KNO 0,5 M 3 fundo são medidos (Figura 3). A curva de calibração da...

Watch this Scientific Journal Video about Dynamic Electrochemical Measurement of Chloride Ions at JoVE.com

Dynamic Electrochemical Measurement of Chloride Ions

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

Dinâmica eletroquímico Medição de íons cloreto

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

dynamic-electrochemical-measurement-of-chloride-ions

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Electrochemical Analyses and Redox Titration

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11.4K visualizações.  University of Twente. Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

Vídeo: Dynamic Electrochemical Measurement of Chloride Ions

Measurement of Ion Concentration in the Unstirred Boundary Layer with Open Patch-Clamp Pipette: Implications in Control of Ion Channels by Fluid Flow

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. Although the molecular mechanisms for the biological responses to fluid flow/shear force are not fully understood, fluid flow-mediated regulation of ion channel gating may contribute critically. Therefore, fluid flow/shear force sensitivity of ion channels has been studied using the patch-clamp technique. However, depending on the experimental protocol, the outcomes and interpretation of data can be erroneous. Here, we present experimental and theoretical evidence for fluid flow-related errors and provide methods for estimating, preventing, and correcting these errors. Changes in junction potential between the Ag/AgCl reference electrode and bathing fluid were measured with an open pipette filled with 3 M KCl. Fluid flow could then shift the liquid/metal junction potential to approximately 7 mV. Conversely, by measuring the voltage shift induced by fluid flow, we estimated the ion concentration in the unstirred boundary layer. In the static condition, the real ion concentrations adjacent to the Ag/AgCl reference electrode or ion channel inlet at the cell-membrane surface can reach as low as approximately 30% of that in the flow condition. Placing an agarose 3 M KCl bridge between the bathing fluid and reference electrode may have prevented this problem of junction potential shifting. However, the unstirred layer effect adjacent to the cell membrane surface could not be fixed in this way. Here, we provide a method for measuring real ion concentrations in the unstirred boundary layer with an open patch-clamp pipette, emphasizing the importance of using an agarose salt-bridge while studying fluid flow-induced regulation of ion currents. Therefore, this novel approach, which takes into consideration the real concentrations of ions in the unstirred boundary layer, may provide useful insight on the experimental design and data interpretation related to fluid shear stress regulation of ion channels.

Mechanosensitive ion channels are often studied in terms of fluid flow/shear force sensitivity with patch-clamp recording. However, depending on the experimental protocol, the outcome on fluid flow-regulations of ion channels can be erroneous. Here, we provide methods for preventing and correcting such errors with a theoretical basis.

Medição da concentração de íons na camada limite Unstirred com pipeta aberto Patch-Clamp: implicações no controle de canais iônicos por fluido fluem

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. ...

Bioquímica

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

Protocolo experimental para determinar o valor de limiar de cloreto para corrosão em amostras colhidas de estruturas de concreto armado

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Engenharia

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

Desbaste eletroquímico de macro e microeletrodos de platina de película fina

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Química

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

The ion concentration polarization (ICP) phenomenon is one of the most prevailing methods to preconcentrate low-abundance biological samples. The ICP induces a noninvasive region for charged biomolecules (i.e., the ion depletion zone), and targets can be preconcentrated on this region boundary. Despite the high preconcentration performances with ICP, it is difficult to find the operating conditions of non-propagating ion depletion zones. To overcome this narrow operating window, we recently developed a new platform for spatiotemporally fixed preconcentration. Unlike preceding methods that only use ion depletion, this platform also uses the opposite polarity of the ICP (i.e., ion enrichment) to stop the propagation of the ion depletion zone. By confronting the enrichment zone with the depletion zone, the two zones merge together and stop. In this paper, we describe a detailed experimental protocol to build this spatiotemporally defined ICP platform and characterize the preconcentration dynamics of the new platform by comparing them with those of the conventional device. Qualitative ion concentration profiles and current-time responses successfully capture the different dynamics between the merged ICP and the stand-alone ICP. In contrast to the conventional one that can fix the preconcentration location at only ~5 V, the new platform can produce a target-condensed plug at a specific location in the broad ranges of operating conditions: voltage (0.5-100 V), ionic strength (1-100 mM), and pH (3.7-10.3).

The protocol for a novel ion concentration polarization (ICP) platform that can stop the propagation of the ICP zone, regardless of the operating conditions is described. This unique ability of the platform lies in the use of merging ion depletion and enrichment, which are two polarities of the ICP phenomenon.

Mesclando Ion polarização de concentração entre justapostos Troca Iônica Membranas para bloquear a propagação da Zona Polarização

The ion concentration polarization (ICP) phenomenon is one of the most prevailing methods to preconcentrate low-abundance biological samples. The ICP ...

Bioengenharia

Precise Electrochemical Sizing of Individual Electro-Inactive Particles

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a means of elucidating heterogeneities that would be masked in ensemble studies. To implement this technique with redox inactive particles, a solution-phase redox reaction is used to produce a steady-state background current on a disk ultramicroelectrode. When a particle adsorbs onto the electrode, it produces a stepwise reduction in the exposed electrode area, which produces, in turn, a stepwise decrease in the current commensurate with the size of the adsorbing species. Historically, however, nanoimpact electrochemistry has suffered from &#34;edge effects,&#34; in which the radial diffusion layer formed at the circumference of the ultramicroelectrodes renders the step size dependent not only on the size of the particle but also on where it lands on the electrode. The introduction of electrocatalytic current generation, however, mitigates the heterogeneity caused by edge effects, thus improving the measurement precision. In this approach, termed &#34;electrocatalytic interruption,&#34; a substrate that regenerates the redox probe at the diffusion layer is introduced. This shifts the rate-limiting step of the current generation from diffusion to the homogeneous reaction rate constant, thus reducing flux heterogeneity and increasing the precision of particle sizing by an order of magnitude. The protocol described here explains the set-up and data collection employed in nanoimpact experiments implementing this effect for improved precision in the sizing of redox in-active materials.

As an analytical technique, nanoimpact electrochemistry, an increasingly important approach to counting and characterizing nanometer-scale, electro-inactive particles, suffers from poor precision due to the heterogeneous current distributions that arise from its use of ultramicroelectrodes. Outlined here is a generalized approach, termed "electrocatalytic interruption," that enhances precision in such measurements.

Dimensionamento eletroquímico preciso de partículas eletro-inativas individuais

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a ...

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called &#8220;concentric&#8221; ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K+]o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na+]o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.

We demonstrate the fabrication, calibration and properties of two types of ion-selective microelectrodes (double-barreled and concentric) for measurement of ion concentrations in brain tissue. These are then used in the mouse hippocampal slice preparation to show that excitatory activity changes both extracellular potassium and sodium concentrations.

Microeletrodos de cano duplo e concêntricos para a medição de Extracelular Ion Signals no tecido cerebral

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular ...

Neurociência

A Micro-agar Salt Bridge Electrode for Analyzing the Proton Turnover Rate of Recombinant Membrane Proteins

To date, more than 50% of all pharmacological drugs target the transport kinetics of membrane proteins. The electrophysiological characterization of membrane carrier proteins reconstituted in lipid bilayer membranes is a powerful but delicate method for the assessment of their physicochemical and pharmacological properties. The substrate turnover number is a unique parameter that allows the comparison of the activity of different membrane proteins. In an electrogenic transport, the gradient of the translocated substrate creates a membrane potential that directly correlates to the substrate turnover rate of the protein. By using silver chloride electrodes, a diffusion potential, also called liquid junction potential, is induced, which alters electrode potential and significantly disturbs precise membrane potential measurements. Diffusion potential can be minimized by a salt bridge, which balances electrode potential. In this article, a micro-agar salt bridge is designed to improve the electrophysiological set-up, which uses micropipettes for the membrane formation. The salt solution is filled into a microcapillary pipette tip, stabilized by the addition of agarose, and can be easily mounted to a standard electrode. The electrode potential of a micro-salt bridge electrode is more stable compared to a standard electrode. The implementation of this system stabilizes electrode potential and allows more precise measurements of membrane potential generated by a pH gradient. Using this system, the proton turnover rates of the mitochondrial carriers UCP1 and UCP3 are reinvestigated and compared to earlier measurements.

In electrophysiological measurements, the presence of a diffusion potential disturbs the precise measurement of the reverse potential by altering the electrode potential. Using a micro-agar salt bridge, the impact of the diffusion potential is minimized, which allows a more precise measurement of substrate turnover numbers of reconstituted recombinant membrane proteins.

Um eletrodo de Micro-agar sal ponte para analisar a taxa de rotatividade de próton de proteínas recombinantes de membrana

To date, more than 50% of all pharmacological drugs target the transport kinetics of membrane proteins. The electrophysiological characterization of ...

A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters

The last 15 years have been characterized by an explosion in the ability to overexpress and purify membrane proteins from prokaryotic organisms as well as from eukaryotes. This increase has been largely driven by the successful push to obtain structural information on membrane proteins. However, the ability to functionally interrogate these proteins has not advanced at the same rate and is often limited to qualitative assays of limited quantitative value, thereby limiting the mechanistic insights that they can provide. An assay to quantitatively investigate the transport activity of reconstituted Cl- channels or transporters is described. The assay is based on the measure of the efflux rate of Cl- from proteoliposomes following the addition of the K+ ionophore valinomycin to shunt the membrane potential. An ion sensitive electrode is used to follow the time-course of ion efflux from proteoliposomes reconstituted with the desired protein. The method is highly suited for mechanistic studies, as it allows for the quantitative determination of key properties of the reconstituted protein, such as its unitary transport rate, the fraction of active protein and the molecular mass of the functional unit. The assay can also be utilized to determine the effect of small molecule compounds that directly inhibit/activate the reconstituted protein, as well as to test the modulatory effects of the membrane composition or lipid-modifying reagents. Where possible, direct comparison between results obtained using this method were found to be in good agreement with those obtained using electrophysiological approaches. The technique is illustrated using CLC-ec1, a CLC-type H+/Cl- exchanger, as a model system. The efflux assay can be utilized to study any Cl- conducting channel/transporter and, with minimal changes, can be adapted to study any ion-transporting protein.

A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters

Proteoliposomes are used to study purified channels and transporters reconstituted in a well-defined biochemical environment. An experimental procedure to measure efflux mediated by these proteins is illustrated. The steps to prepare proteoliposomes, perform the recordings, and analyze data to quantitatively determine the functional properties of the reconstituted protein are described.

A proteolipossoma-Based Efluxo Ensaio para determinar as propriedades de uma única molécula de Cl<sup&gt; -</sup&gt; Canais e Transportadores

The last 15 years have been characterized by an explosion in the ability to overexpress and purify membrane proteins from prokaryotic organisms as well as ...

Biologia

Measurement of Extracellular Ion Fluxes Using the Ion-selective Self-referencing Microelectrode Technique

Cells from animals, plants and single cells are enclosed by a barrier called the cell membrane that separates the cytoplasm from the outside. Cell layers such as epithelia also form a barrier that separates the inside from the outside or different compartments of multicellular organisms. A key feature of these barriers is the differential distribution of ions across cell membranes or cell layers. Two properties allow this distribution: 1) membranes and epithelia display selective permeability to specific ions; 2) ions are transported through pumps across cell membranes and cell layers. These properties play crucial roles in maintaining tissue physiology and act as signaling cues after damage, during repair, or under pathological condition. The ion-selective self-referencing microelectrode allows measurements of specific fluxes of ions such as calcium, potassium or sodium at single cell and tissue levels. The microelectrode contains an ionophore cocktail which is selectively permeable to a specific ion. The internal filling solution contains a set concentration of the ion of interest. The electric potential of the microelectrode is determined by the outside concentration of the ion. As the ion concentration varies, the potential of the microelectrode changes as a function of the log of the ion activity. When moved back and forth near a source or sink of the ion (i.e. in a concentration gradient due to ion flux) the microelectrode potential fluctuates at an amplitude proportional to the ion flux/gradient. The amplifier amplifies the microelectrode signal and the output is recorded on computer. The ion flux can then be calculated by Fick&#8217;s law of diffusion using the electrode potential fluctuation, the excursion of microelectrode, and other parameters such as the specific ion mobility. In this paper, we describe in detail the methodology to measure extracellular ion fluxes using the ion-selective self-referencing microelectrode and present some representative results.

Transporters in cell membranes allow differential segregation of ions across cell membranes or cell layers and play crucial roles during tissue physiology, repair and pathology. We describe the ion-selective self-referencing microelectrode that allows the measurement of specific ion fluxes at single cells and tissues in vivo.

Medição de Extracelular Ion Fluxos Usando a técnica microeletrodos de auto-referência íon-seletivo

Cells from animals, plants and single cells are enclosed by a barrier called the cell membrane that separates the cytoplasm from the outside. Cell layers ...

Electrochemical Measurements of Supported Catalysts Using a Potentiostat/Galvanostat

Source: Laboratory of Dr. Yuriy Rom&#225;n &#8212; Massachusetts Institute of Technology
A potentiostat/galvanostat (often referred to as simply a potentiostat) is an instrument that measures current at an applied potential (potentiostatic operation) or measures potential at an applied current (galvanostatic operation) (Figure 1). It is the most commonly used instrument in the electrochemical characterization of anode and cathode materials for fuel cells, electrolyzers, batteries, and supercapacitors.
Conventionally, these anode and cathode materials are interfaced with a potentiostat via a three-electrode electrochemical cell. The electrode leads from the potentiostat are connected to the reference electrode, the counter electrode (often called the auxiliary electrode), and the working electrode (which contains the test material of interest). The electrochemical cell is then filled with a high ionic strength electrolyte solution, such as an acidic, alkaline, or salt solution. The media for this high ionic strength solution is typically aqueous; however, for applications necessitating higher operating cell potential windows, such as batteries and supercapacitors, non-aqueous media is often used. The cell media is degassed with an inert gas (to prevent unwanted side reactions) or with a test gas (if the test reaction involves a gas at one of the electrodes).
Alternatively, a salt bridge or membrane is employed to maintain ionic contact if the two half cells are to be measured in different electrolytes. In heterogeneous electrocatalysis, this type of &#34;two compartment&#34; cell is often used if the test molecule at the working electrode is also reactive at the counterelectrode. This happens frequently as the counterelectrode typically employed is platinum, which is a highly active catalyst for many reactions. Here, single compartment cells will be used, where all three electrodes are in the same media.
This video will explain the process of polishing a working electrode, preparing a catalyst ink, mounting the catalyst ink onto the working electrode, preparing the electrochemical cell, and then performing electrochemical measurements. The measurements that are performed include: cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronopotentiometry (CP), and chronoamperometry (CA).
<img alt="Figure 1" src="/files/ftp_upload/5698/5698fig1.jpg" /> 
Figure 1. An example of a single compartment electrochemical cell. a.) Teflon cap, b.) glass cell, c.) Pt wire counter electrode, d.) working electrode, e.) Ag/AgCl reference electrode, f.) 0.5 M aqueous sulfuric acid electrolyte solution.

Dinâmica eletroquímico Medição de íons cloreto

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