Concentrating molecules in a simple microchannel (original) (raw)
Related papers
Numerical studies of electrokinetic control of DNA concentration in a closed-end microchannel
ELECTROPHORESIS, 2010
A major challenge in lab-on-a-chip devices is how to concentrate sample molecules from a dilute solution, which is critical to the effectiveness and the detection limit of on-chip bio-chemical reactions. A numerical study of sample concentration control by electrokinetic microfluidic means in a closed-end microchannel is presented in this paper. The present method provides a simple and efficient way of concentration control by using electrokinetic trapping of a charged species of interest, controlling liquid flow and separating different sample molecules in the microchannel. The electrokinetic-concentration process and the controlled transport of the sample molecules are numerically studied. In this system, in addition to the electroosmotic flow and the electrophoresis, the closed-end of the chamber causes velocity variation at both ends of the channel and induces a pressure gradient and the associated fluid movement in the channel. The combined effects determine the final concentration field of the sample molecules. The influences of a number of parameters such as the channel dimensions, electrode size and the applied electric field are investigated.
This paper presents a numerical study of controlling the flow rate and the concentration in a microchannel network by utilizing induced-charge electrokinetic flow (ICEKF). ICEKF over an electrically conducting surface in a microchannel will generate vortices, which can be used to adjust the flow rates and the concentrations in different microchannel branches. The flow field and concentration field were studied under different applied electric fields and with different sizes of the conducting surfaces. The results show that, by using appropriate size of the conducting surfaces in appropriate locations, the microfluidic system can generate not only streams of the same flow rate or linearly decreased flow rates in different channels, but also different, uniform concentrations within a short mixing length quickly.
Bioanalysis, 2014
Sample preparation is the first part of every analytical method, but is often considered only after optimization of the method. It is traditionally performed using a range of highly manual techniques, with solid-phase extraction, liquid-liquid extraction, protein precipitation, ultracentrfiguation, etc, being used depending on the targets and the application. Here, we will focus on alternatives based on electrokinetics for applications including sample clean up, concentration and derivatisation of large biological molecules (DNA, peptides, and proteins) of diagnostic importance, as well as small molecules as a tool for therapeutic drug monitoring. The review describes these approaches in terms of mechanism, applicability and potential to be integrated into a lab on a chip device for directly processing biological samples.
ELECTROPHORESIS, 2010
Here we present a scheme to separate particles according to their characteristic physical properties, including size, charge, polarizability, deformability, surface charge mobility, dielectric features, and local capacitance. Separation is accomplished using a microdevice based on direct current insulator gradient dielectrophoresis that can isolate and concentrate multiple analytes simultaneously at different positions. The device is dependent upon dielectrophoretic and electrokinetic forces incorporating a global longitudinal direct current field as well as using shaped insulating features within the channel to induce local gradients. This design allows for the production of strong local field gradients along a global field causing particles to enter, initially transported through the channel by electrophoresis and electroosmosis (electrokinetics), and to be isolated via repulsive dielectrophoretic forces that are proportional to an exponent of the field gradient. Sulfate-capped polystyrene nano and microparticles (20, 200 nm, and 1 mm) were used as probes to demonstrate the influence of channel geometry and applied longitudinal field on separation behavior. These results are consistent with models using similar channel geometry and indicate that specific particulate species can be isolated within a distinct portion of the device, whereas concentrating particles by factors from 10 3 to 10 6 .
Manipulating particles in microfluidics by floating electrodes
ELECTROPHORESIS, 2010
Various particle manipulations including enrichment, movement, trapping, separation, and focusing by floating electrodes attached to the bottom wall of a straight microchannel under an imposed DC electric field have been experimentally demonstrated. In contrast to a dielectric microchannel possessing a nearly uniform surface charge (or z potential), the metal strip (floating electrode) is polarized under the imposed electric field, resulting in a nonuniform distribution of the induced surface charge with a zero net surface charge along the floating electrode's surface, and accordingly induced-charge electroosmotic flow near the metal strip. The induced induced-charge electroosmotic flow can be regulated by controlling the strength of the imposed electric field and affects both the hydrodynamic field and the particle's motion. By using a single floating electrode, charged particles could be locally concentrated in a section of the channel or in an endreservoir and move toward either the anode or the cathode by controlling the strength of the imposed electric field. By using double floating electrodes, negatively charged particles could be concentrated between the floating electrodes, subsequently squeezed to a stream flowing in the center region of the microchannel toward the cathodic reservoir, which can be used to focus particles.
A new focusing model and switching approach for electrokinetic flow inside microchannels
Journal of Micromechanics and Microengineering, 2005
This paper presents an investigation into two crucial aspects of microfluidic applications, namely electrokinetic focusing and switching. This study commences by modeling the electrokinetic focusing phenomenon theoretically using the potential flow theory. A new theoretical model is derived and applied to predict the width of the focused stream. The results predicted by the theoretical model are shown to be in good agreement with the experimental data. The paper then proceeds to study the electrokinetic switching functions systematically using both experimental and theoretical approaches. A new control model for 'one-to-multiple' electrokinetically pre-focused micro flow switches is proposed. Using this new model, the sample flow can be pre-focused electrokinetically into a narrow stream and then injected directly into the desired outlet port. The results of this study provide a useful methodology for the analysis of flow control in microfluidic devices. Finally, an electrokinetically driven micro flow cytometer utilizing electrokinetic focusing and switching effects is demonstrated. Experimental data show that the developed methods could successfully focus microparticles and direct them into any desired outlet port.
Passive electrophoresis in microchannels using liquid junction potentials
ELECTROPHORESIS, 2002
The formation of the liquid junction potential (LJP) is a well-studied phenomenon that occurs in the presence of ionic concentration gradients. Although the LJP has been well characterized, its impact has generally been overlooked in microfluidic applications. The characteristics of flow in microfluidic channels cause this phenomenon to be particularly important, both as a source of deviation from anticipated results and as a tool capable of being harnessed to perform useful tasks. It is demonstrated that LJPs formed in microchannels can induce appreciable electrophoretic transport of charged species without the use of electrodes or an external power supply. This process is demonstrated in an H-filter (an H-shaped microfluidic channel used to bring two fluids into contact allowing extraction of diffusing species from one stream to another) by generating junction potentials between two flowing streams containing different concentrations of strong electrolytes and observing the mass transport of the charged dye fluorescein between those streams. It is shown that the LJP can be controlled to either accelerate or decelerate mass transport across a fluid interface in the absence of an interposed membrane. A preliminary mathematical description of the phenomena is offered to support the hypothesis that the observed mass transport is a result of the LJP. Possible practical microfluidic applications of electrophoretic transport without electrodes are discussed.
Electric Control of Droplets in Microfluidic Devices
Angewandte Chemie International Edition, 2006
The precision manipulation of streams of fluids with microfluidic devices is revolutionizing many fluid-based technolo-gies and enabling the development of high-throughput reactors that use minute quantities of reagents. However, as the scale of these reactors shrinks, contamination effects due to surface adsorption and diffusion limit the smallest quantities that can be used. The confinement of reagents in droplets in an immiscible carrier fluid overcomes these limitations, but demands new fluid-handling technology. We present a platform technology based on charged droplets and electric fields that enables electrically addressable droplet generation, highly efficient droplet coalescence, precision droplet breaking and recharging, and controllable droplet sorting. This is an essential enabling technology for a high-throughput droplet microfluidic reactor.