Search

A peculiar method used for particle separation device in microfluidics is hydrodynamic filtration. To achieve the filtration of sample fluid with particle, this is the technique which concedes two-input (with buffer inlet) sheath fluid to conflow at distinct velocity rates in a sifter-shaped microchannel network demonstrated. The objective is to assure the separation of particles based on size and mass in microflow network with grooves or rectangular cross section by hydrodynamic filtration. However, simulation is done to examine the particle tracing with mass by sifter-shaped microchannel network using COMSOL Multiphysics software. The size, mass and density of the particle are related to the properties of K. pneumoniae and blood particles samples. During the experiments, different networks were designed and simulated to acquire a better filtration effect and particle separation based on size and mass. After the simulation done for the networks, it resulted that sifter-shaped microchannel network shows a precise separation of K. pneumoniae particle. Analysis of a microchannel having distinct angles (90°, 15°, 25° and 35°) with individual inflow velocity for sample with particle and buffer inflow velocity without particle at 3000 µl/s and with various other flow rates for blood and 50 µl/s and with various other flow rates for water was performed, where sifter-shaped microchannel device consisting of 90° and 25° sifter structure provides a preferable separation through the targeted outlet 4 and outlet 1 of microchannel for a larger bioparticles and smaller particles (blood cells) through the other outlets of device.

Fourier-transformed large amplitude alternating current voltammetry (FTACV) provides a sensitive analytical tool for the discrimination of electrode reactions that are complicated by surface heterogeneity. In this paper, it is shown how the FTACV response at a dual-electrode system comprised of different electrode materials having different heterogeneous charge transfer (k01 and k02) can be resolved into its individual electrode kinetics components without prior knowledge of the electrode size ratio (θ1:θ2). This is possible when one process is reversible and the other is quasi-reversible; achievable by careful selection of the FTACV frequency. The applicability of the FTACV method over a wide range of electrode kinetic values and size ratios is considered for conditions under which numerical simulations based on a 1D diffusion model are adequate to describe the mass transport problem.

A conducting polymer-modified electrode was proposed in this article, which was fabricated by electropolymerization of 5-amino-1H-tetrazole (ATet) on a glassy carbon electrode. Electrochemical studies such as differential pulse voltammetry and chronoamperometry were performed for the evaluation of the rate constant of the catalytic reaction, the diffusion coefficient of the analyte dopamine, and the linear dynamic range of the analyte determination. The film modified electrode has superior resolving power in quantitative determination from the mixture of analytes and it was found to be an efficient functionalized electrode for its sensitivity and selectivity toward the analyte of interest.

Theory for cyclic square wave voltammetry of electrode reactions with coupled chemical reactions following the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics.

Separation micro-particles based on physical characteristics is important in numerous applications such as diagnostics, biological analyses, food industries and chemical processing. Microfluidic devices have emerged as a multifunctional and powerful platform for separation ranging from nano-micro sized particles to biological cells. This paper presents a simulation study for microparticle separation in a microfluidic channel based on hydrodynamic technique. By exploiting the hydrodynamic properties of the fluid flow and physical characteristics of microparticles, effective size-based separation is demonstrated. The objectives of the simulations are to obtain the appropriate channels’ angle to separate micro-particle. The analysis of effects of taper angle for microparticle separation was carried out using numerical solutions from the finite element ABAQUS-FEA software. The taper angles 20° and 25° are successfully separate the mixture of 1000 kgm−3 and 10000 kgm−3 density microparticle.

Cyclic voltammetry curves of two kinds of electrode reactions based on a simple E mechanism with unequal diffusion coefficients and the ECirre mechanism under convergent, linear and 'mixed' (convergent/linear) diffusion conditions are developed by numerical simulation. We show that these two types of distinct electrode reactions can respond almost identically under cyclic voltammetry and with similar variation with scan rate under mixed and linear diffusion conditions.

International audience; Electrochemical analysis of species known to passivate electrode surfaces remains challenging. We previously proposed a new method dealing with sampled-current voltammetry performed on an electrode array to mimic polarography at a dropping mercury electrode for the detection of copper. In this work, we study the effectiveness of this method to circumvent electrode fouling with the analysis of phenol solutions at high concentrations (10-2 mol L-1), known to polymerize on electrode surface during its oxidation. Electrode arrays well-adapted to the analysis with such system are prepared by photolithography and characterized by X-Ray photoelectron spectroscopy, X-ray diffraction and voltammetry. While analyses performed in conventional linear voltammetry or sampled-current voltammetry on a single electrode are considerably affected by electrode fouling, a linear calibration plot was achievable using our method. Modelling of the electrochemical signal showed that the current depends only on the applied potential and a parameter characteristic of the passivation phenomenon. It also underlined that sampled-current voltammetry on electrode array can circumvent the problem of passivation by a judicious choice of the sampling time.

Single cell analysis has emerged as a paradigm shift in cell biology to understand the heterogeneity of individual cells in a clone for pathological interrogation. Microfluidic droplet technology is a compelling platform to perform single cell analysis by encapsulating single cells inside picoliter-nanoliter (pL-nL) volume droplets. However, one of the primary challenges for droplet based single cell assays is single cell encapsulation in droplets, currently achieved either randomly, dictated by Poisson statistics, or by hydrodynamic techniques. In this paper, we present an interfacial hydrodynamic technique which initially traps the cells in micro-vortices, and later releases them one-to-one into the droplets, controlled by the width of the outer streamline that separates the vortex from the flow through the streaming passage adjacent to the aqueous-oil interface (dgap). One-to-one encapsulation is achieved at a dgap equal to the radius of the cell, whereas complete trapping of the cells is realized at a dgap smaller than the radius of the cell. The unique feature of this technique is that it can perform 1. high efficiency single cell encapsulations and 2. size-selective capturing of cells, at low cell loading densities. Here we demonstrate these two capabilities with a 50% single cell encapsulation efficiency and size selective separation of platelets, RBCs and WBCs from a 10× diluted blood sample (WBC capture efficiency at 70%). The results suggest a passive, hydrodynamic micro-vortex based technique capable of performing high-efficiency single cell encapsulation for cell based assays.

There are several protecting techniques managing with contamination on optical surfaces of in-vessel diagnostic components in ITER. Analysis of impurity transport in narrow and curved gaps gave us the idea that it can’t be explained by convection flows. The proposed protecting construction, situated between plasma and irradiating laser mirror launcher, was analysed for effectiveness. The protecting ability of this construction is based on the principles of hydrodynamic, in particular on bevelled entrance, which provides redirection of polluting gas flow away from the optical components due to angling optical and geometrical channel axes. Several different numerical simulations were studied. The design, setting objectives as well as equations and parameters are under discussion. Results of 2D and 3D numerical simulations are provided.

Size exclusion chromatography (SEC) or gel filtration is a hydrodynamic technique that separates molecules in solution as a function of their size and shape. In the case of proteins, the hydrodynamic value that can be experimentally derived is the Stokes radius (R(s)), which is the radius of a sphere with the same hydrodynamic properties (i.e., frictional coefficient) as the biomolecule. Determination of R(s) by SEC has been widely used to monitor conformational changes induced by the binding of calcium (Ca(2+)) to many Ca(2+)-sensor proteins. For this class of proteins, SEC separation is based not just on the variation in protein size following Ca(2+) binding, but likely arises from changes in the hydration shell structure. This protocol aims to describe a gel filtration experiment on a prepacked column using a Fast Protein Liquid Chromatography (FPLC) system to determine the R(s) of proteins with some indications that are specific for Ca(2+) sensor proteins.

The theory of three step electrode reaction is developed for square wave voltammetry on stationary spherical electrodes. It was assumed that all electroactive species are solution soluble. The dependence of the response on the thermodynamic stability of intermediates, on the electrode radius and the scan direction is investigated for the fast and reversible electrode reactions. The criterion of reversibility is postulated. Furthermore, the influence of electrode kinetics on the response was calculated for the cathodic and anodic scan directions. The difference in responses caused by the variation of scan direction is an indication of multiple electron transfers. The method for the estimation of transfer coefficient is demonstrated. This work is licensed under a Creative Commons Attribution 4.0 International License.

There are several strategies for enhancing the sensitivity of electroanalytical methods. Usually, those strategies are based on the selection of the voltammetric technique, the inclusion of an accumulation step, and the eventual addition of a catalytic chemical reaction that regenerates the electroactive species. Square-wave voltammetry (SWV) is one of the most sensitive techniques. In the case of electroanalytical applications, it is typically preceded by an electrochemical or adsorptive pre-concentration step. In this manuscript, the theory of SWV for a quasi-reversible electrode process coupled to a catalytic chemical reaction between an adsorbed reagent and a soluble product is presented. The dependences of the dimensionless net peak current and its peak potential on the value of the standard charge transfer rate constant are described. The variation of the SWV parameters such as frequency and potential pulse amplitude are discussed. The effect of the chemical and electrochemical kinetics on the voltammetric profile is analyzed. Fil: Vettorelo, Sabrina Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina Fil: Garay, Fernando Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentina

An apparatus for the measurement of steady-state microelectrode voltammetry at elevated temperatures is described. The scope of this experimental approach as a method for the determination of diffusion coefficients at variable temperatures in the case of simple one-electron processes is demonstrated. Diffusion coefficients over a range of temperatures are derived for N,N,N′N′-tetramethylphenylenediamine in both acetonitrile and water solvents, tris-4-bromophenylamine in acetonitrile, and ferrocene in acetonitrile and dimethylformamide from which activation energies for diffusion are obtained. Diffusion coefficient values are used to derive Stokes-Einstein radii for each species in solution. The electroreductions of o-bromonitrobenzene in dimethylformamide and 9-chloroanthracene in acetonitrile are studied as a function of temperature and activation energies estimated for carbon-halide bond cleavage in the corresponding radical anions.

A simple equation is presented which relates the diffusion layer thickness at a rotating disk electrode to the average diffusion layer thickness at a channel (or tubular) electrode, under the assumption that the hydrodynamic flow in both cases is laminar. It is demonstrated that, through the equation, the parameters characterising various possible electrode reaction mechanisms (ECE, DISP1, EC', CE,⋯) under transport-limited conditions at one of the two electrodes, are readily deduced once the corresponding mass transport problem has been rigorously solved at the other electrode. In addition, the relationship is shown to be equally successful when considering the chronoamperometric response at the two electrodes to a potential step, from a region in which no current flows to one corresponding, under steady-state conditions, to the passage of the transport-limited current, and also for the description of the general form of the current-potential curves for the two electrode geometries. The circumstances under which the transformation may be applied are critically assessed.

The theory of cyclic voltammetry at disc electrodes and microelectrodes is developed for a system where the electroactive reactant is regenerated in solution using a catalyst. This catalytic process is of wide importance, not least in chemical sensing, and it can be characterized by the resulting peak current which is always larger than that of a simple electrochemical reaction; in contrast the reverse peak is always relatively diminished in size. From the theoretical point of view, the problem involves a complex physical situation with two-dimensional mass transport and non-uniform surface gradients. Because of this complexity, hitherto the treatment of this problem has been tackled mainly by means of numerical methods and so no analytical expression was available for the transient response of the catalytic mechanism in cyclic voltammetry when disc electrodes, the most popular practical geometry, are used. In this work, this gap is filled by presenting an analytical solution for the application of any sequence of potential pulses and, in particular, for cyclic voltammetry. The induction principle is applied to demonstrate mathematically that the superposition principle applies whatever the geometry of the electrode, which enabled us to obtain an analytical equation valid whatever the electrode size and the kinetics of the catalytic reaction. The theoretical results obtained are applied to the experimental study of the electrocatalytic Fenton reaction, determining the rate constant of the reduction of hydrogen peroxide by iron(II).

Both the strongly implicit procedure and the alternating direction implicit finite difference (ADI) technique are used to simulate mass transport to a microdisc electrode located in a channel flow, taking account of diffusion in three dimensions and the parabolic laminar convective flow over the electrode surface. The effect of the latter on the shape of the disc diffusion layer is qualitatively identified. The flow rate dependence of the transport-limited disc current is predicted and shown to be in quantitative agreement with experiments conducted on the oxidation of ferrocene in acetonitrile solution. © 1995 American Chemical Society.

Epigenetic modifications have been associated by many studies with several types of diseases and metabolic dysfunctions. Specifically, N7-methyl modification of guanine (7-mG) is well established to be used as a biomarker for the detection and determination of DNA methylation. The use of an electrochemical sensor has the potential to provide a simpler and more economic sensing methodology for the determination of 7-mG compared to traditionally utilised laboratory based approaches. In this paper we demonstrate the feasibility of an electrochemical sensor which could potentially be easily applied towards the determination of 7-mG within biological samples, such as human urine. A practical electrochemical configuration was employed consisting of a boron-doped diamond electrode (BDD) as the working electrode and a screen-printed graphite electrode (SPE) providing the counter electrode and the reference electrode. With this new protocol, the electrochemical behaviour of 7-mG has been investigated via cyclic voltammetry (CV) and square wave voltammetry (SWV) using a BDD electrode with a simplified electrochemical set-up. The electrochemical behaviour of 7-mG within acetate buffer solutions at a BDD electrode has been compared and contrasted to a glassy carbon electrode with the following parameters studied: voltammetric scan rate, solution pH, 7-mG concentration and electrode surface pretreatment. The oxidative mechanism elucidation has been performed at controlled potential and such results have provided the dimer formation as the major product. The simultaneous electroanalytical identification of 7-mG together with the presence of guanine, adenine and 8-oxoguanine has been investigated under the optimum experimental conditions. Furthermore, the feasibility of using a BDD electrode for the detection of 7-mG is explored in a human urine sample. Authors would like to acknowledge funding throughout the University of Alicante. J. Iniesta thanks the programme Salvador de Madariaga from the Ministerio de Economía y Competitividad, grant number PRX14/00363.

As a complement to a previous contribution from us, the mass transport mechanisms of the electroactive species to and from the electrode in an uncomplicated electrode mechanism are considered. The electrode process as a whole is discussed, with emphasis to its reversibility degree, as results from the relevant responses in controlled potential techniques, such as chronoamperometry and current sampling voltammetry, linear sweep and cyclic voltammetry, and in rotating disk voltammetry. The electrode process as a whole, composed by charge transfer and mass transport steps that concur to condition the current flowing, is analysed on the basis of the relative rates of the two steps, as well of the time window within which the process is observed. The so-called ‘boundary value problem’ for uncomplicated charge transfers with different reversibility degrees is outlined. Supplementary Material is available, in which the simulated concentration profiles for reduced and oxidised species reacting at an electrode, at which a triangular potential waveform is applied, are linked to the corresponding current densities.

This work presents a low-cost microfluidic device with sensitive, in-channel electrochemical detection capabilities in microfluidic device. This is accomplished using in-channel gold microelectrodes. The detection unit is composed of (i) the working electrodes (WE) with (ii) a common pseudo-reference electrode (RE) in gold and (iii) a counter electrode (CE) made with indium tin oxide (ITO) on a glass substrate. A redox solution ferrocyanide/ferricyanide was flowed through the microfluidic channel in order to test sensing capabilities using cyclic voltammetry (CV). This solution was confined by an electrochemically inactive solution (ultra-pure water) in the same channel. The position of the interface between the redox solution and the confinement solution could be changed via the ratio between their volumetric flow rates. Cyclic voltammetry allowed the detection of electro active species with reduction current of 150 nA.

Theory for cyclic square wave voltammetry of electrode reactions with chemical reactions preceding the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics.

In this study, a one-dimensional stochastic model based on the random walk approach is used to simulate cyclic voltammetry. The model takes into account mass transport, kinetics of the redox reactions, adsorption effects and changes in the morphology of the electrode. The model is shown to display the expected behavior. Furthermore, the model shows consistent qualitative agreement with a finite difference solution. This approach allows for an understanding of phenomena on a microscopic level and may be useful for analyzing qualitative features observed in experimentally recorded signals.

To perform specific analysis for the single cell, individual cells have to be captured and separated from each other before further treatments and analysis can be carried out. This paper presents the design, simulation, fabrication, and testing of a microfluidic device for trapping a single cell/particle based on a hydrodynamic technique. A T-channel trapping chip has been proposed to provide single-cell trapping and consequently could be a platform for cell treatments and manipulations. A finite element T-channel trapping model was developed using Abaqus FEA™ software to observe it’s trapping ability by optimizing the channel’s geometry and RhMain/RhTrap ratio. A proof of concept demonstration for cell trapping in the T-channel model was presented in the simulation analysis and experimental work using HUVEC cell aggregate. The T-channel was found to be able to trap a single cell via the hydrodynamic trapping concept using an appropriate channel geometry and RhMain/RhTrap ratio. The proposed T-channel single-cell trapping has potential application for single cell characterization and single 3D cell aggregates treatments and analysis.

(J. Phys. Chem. C (2012) 116:20 (10913-10916) DOI: 10.1021/jp2118696)