A microfluidic electroosmotic mixer and the effect of potential and frequency on its mixing efficiency

This paper presents the design and numerical simulation of a T-shape microfluidic electroosmotic micromixer. It is equipped with six microelectrodes that are embedded in the side surfaces of the microchannel. The electrode array consists of two sets of three 20 &Acirc;&iquest;m and 60 &Acirc;&iquest;m microelectrodes arranged in the form of two opposing triangles. Numerical analysis of electric potential and frequency effects on mixing efficiency of the micromixer is carried out by means of two sets of simulations. First, the electric potential is kept at 2 V while the frequency is varied within 10-50 Hz. The highest achieved mixing efficiency is 96% at 22 Hz. Next, the frequency is kept at 30 Hz whilst the electric potential is varied within 1-5 V. The best achieved mixing efficiency is 97% at 3 V.<br /

Fabrication and Flow Dynamics Analysis of Micromixer for Lab-on-a-Chip Devices

The miniaturized systems designed for lab-on-a-chip (LOC) technologies are generally implemented with a micro-scale mixer to provide intimate contact between the reagent molecules for interactions and chemical reactions. The exponential increase of research in microfabrication and microfluidic applications highlights the importance of understanding the theory and mechanism that governs mixing at the microscale level. In this study, the fabrication of an active and passive micromixer was discussed. The optimized state of art soft lithography and 3D printing was used as a microfabrication technique. The challenges at different fabrication steps were presented along with the modifications. Microelectrodes were integrated with the active microfluidic mixer to create an electrokinetic effect. The fluid flow field inside the micromixerwas characterized by the Micro Particulate Image Velocimetry (Micro-PIV) system. Besides, numerical simulations were performed on 2D and 3D micromixers. Finally, results obtained in experiment and numerical simulations were analyzed to get a better understanding of the micromixer design

Microfluidic Mixing: A Review

The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers

Micro/Nano-Chip Electrokinetics

Micro/nanofluidic chips have found increasing applications in the analysis of chemical and biological samples over the past two decades. Electrokinetics has become the method of choice in these micro/nano-chips for transporting, manipulating and sensing ions, (bio)molecules, fluids and (bio)particles, etc., due to the high maneuverability, scalability, sensitivity, and integrability. The involved phenomena, which cover electroosmosis, electrophoresis, dielectrophoresis, electrohydrodynamics, electrothermal flow, diffusioosmosis, diffusiophoresis, streaming potential, current, etc., arise from either the inherent or the induced surface charge on the solid-liquid interface under DC and/or AC electric fields. To review the state-of-the-art of micro/nanochip electrokinetics, we welcome, in this Special Issue of Micromachines, all original research or review articles on the fundamentals and applications of the variety of electrokinetic phenomena in both microfluidic and nanofluidic devices

Analysis, Design and Fabrication of Micromixers, Volume II

Micromixers are an important component in micrototal analysis systems and lab-on-a-chip platforms which are widely used for sample preparation and analysis, drug delivery, and biological and chemical synthesis. The Special Issue "Analysis, Design and Fabrication of Micromixers II" published in Micromachines covers new mechanisms, numerical and/or experimental mixing analysis, design, and fabrication of various micromixers. This reprint includes an editorial, two review papers, and eleven research papers reporting on five active and six passive micromixers. Three of the active micromixers have electrokinetic driving force, but the other two are activated by mechanical mechanism and acoustic streaming. Three studies employs non-Newtonian working fluids, one of which deals with nano-non-Newtonian fluids. Most of the cases investigated micromixer design

Magnetic bead-based DNA extraction and purification microfluidic chip

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A magnetic bead-based DNA extraction and purification device has been designed to be used for extraction of the target DNA molecules from whole blood sample. Mixing and separation steps are performed using functionalised superparamagnetic beads suspended in the cell lysis buffer in a circular chamber that is sandwiched between two electromagnets. Non-uniform nature of the magnetic field causes temporal and spatial distribution of the beads within the chamber. This process efficiently mixes the lysis buffer and whole blood in order to extract DNA from target cells. Functionalized surface of the magnetic beads then attract the exposed DNA molecules. Finally, DNA-attached magnetic beads are attracted to the bottom of the chamber by activating the bottom electrode. DNA molecules are extracted from the magnetic beads by washing and re-suspension processes. The numerical simulation approach has been adopted in order to design the magnetic field source. The performance of the magnetic field source has been investigated against different physical and geometrical parameters and optimised dimensions are obtained with two different magnetic field sources; integrated internal source and external source. A new magnetic field pattern has been introduced in order to efficiently control the bulk of magnetic beads inside the mixing chamber by dynamic shifting of magnetic field regions from the centre of the coils to the outer edge of the coils and vice versa. A Matlab code has been developed to simulate beads trajectories inside the designed extraction chip in order to investigate the efficiency of the magnetic mixing. A preliminary target molecule capturing simulation has also been performed using the simulated bead trajectories to evaluate the DNA-capturing efficiency of the designed extraction chip. The performance of the designed extraction chip has been tested by conducting a series of biological experiments. Different magnetic bead-based extraction kits have been used in a series of preliminary experiments in order to extract a more automation friendly extraction protocol. The efficiency of the designed device has been evaluated using the spiked bacterial DNA and non-pathogenic bacterial cell cultures (B. subtilis, Gram positive bacteria and E. coli, Gram negative bacteria) into the blood sample. Excellent DNA yields and recovery rates are obtained with the designed extraction chip through a simple and fast extraction protocol

Theoretical and numerical studies of chaotic mixing

Theoretical and numerical studies of chaotic mixing are performed to circumvent the difficulties of efficient mixing, which come from the lack of turbulence in microfluidic devices. In order to carry out efficient and accurate parametric studies and to identify a fully chaotic state, a spectral element algorithm for solution of the incompressible Navier-Stokes and species transport equations is developed. Using Taylor series expansions in time marching, the new algorithm employs an algebraic factorization scheme on multi-dimensional staggered spectral element grids, and extends classical conforming Galerkin formulations to nonconforming spectral elements. Lagrangian particle tracking methods are utilized to study particle dispersion in the mixing device using spectral element and fourth order Runge-Kutta discretizations in space and time, respectively. Comparative studies of five different techniques commonly employed to identify the chaotic strength and mixing efficiency in microfluidic systems are presented to demonstrate the competitive advantages and shortcomings of each method. These are the stirring index based on the box counting method, Poincare sections, finite time Lyapunov exponents, the probability density function of the stretching field, and mixing index inverse, based on the standard deviation of scalar species distribution. Series of numerical simulations are performed by varying the Peclet number (Pe) at fixed kinematic conditions. The mixing length (lm) is characterized as function of the Pe number, and lm ∝ ln(Pe) scaling is demonstrated for fully chaotic cases. Employing the aforementioned techniques, optimum kinematic conditions and the actuation frequency of the stirrer that result in the highest mixing/stirring efficiency are identified in a zeta potential patterned straight micro channel, where a continuous flow is generated by superposition of a steady pressure driven flow and time periodic electroosmotic flow induced by a stream-wise AC electric field. Finally, it is shown that the invariant manifold of hyperbolic periodic point determines the geometry of fast mixing zones in oscillatory flows in two-dimensional cavity

Generating efficient chaos effect in micro channel using electrohydrodynamic theory

AC electro-osmotic flow is a promising technique in microfluidic manipulation. AC electroosmotic force has been generated inside a novel twisted micro channel in order to overcome the low Reynolds number fluid. The behavior of concentration distribution has been investigated by solving the transient electric field, fluid mechanic and convection-diffusion theory inside the channel. Two particles have been released inside the channel to investigate the efficiency of generated chaotic regime. Velocity streamlines and perturbation of species concentration reveal high performance stirring process which above 95% mixing efficiency achieved for 210 μm channel length. The efficiency increases by increasing the applied voltage amplitude. Geometrical and exciting parameters have been optimized in order to maximize the efficiency of mixing process and avoid electrolysis and sample damage