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At least 1,189 records · Page 66Linked to original sources
PubMed2002

A passive pumping method for microfluidic devices.

The surface energy present in a small drop of liquid is used to pump the liquid through a microchannel. The flow rate is determined by the volume of the drop present on the pumping port of the microchannel. A flow rate of 1.25 microL s(-1) is demonstrated using 0.5 microL drops of water. Two other fluid manipulations are demonstrated using the passive pumping method: pumping liquid to a higher gravitational potential energy and creating a plug within a microchannel.

Journal Article↗
PubMed2003

Fibre optic coupler as a detector for microfluidic applications.

A new construction of a fibre optic coupler is presented in the paper. Two polymer optical fibres were used to build a coupler in which coupling efficiency of optical power depends on the refractive index of liquid delivered to a microchannel formed by the fibres. The coupler was tested as a detector in saccharose concentration measurements, and was used in absorbance measurements. A red light emitting diode and a spectrometer were used as a light source and a photodetector, respectively. Experiments confirmed that the coupler can be used for the real time monitoring of the changes in the refractive index of a saccharose solution exhibiting repeatable changes in the signal, with no hysteresis. Absorbance tests were performed with a solution of bromothymol blue at different pH.

Journal Article↗
PubMed2003

Sub-second isoelectric focusing in free flow using a microfluidic device.

Using a microfabricated chip with a bed volume of 0.2 microL we demonstrate the validity of the scaling laws for molecular mass transport of isoelectric focusing (IEF) in free flow. Nano- or microlitre sample volumes can be concentrated within 430 ms by a factor of up to 400. These very fast performances make the chip applicable to proteomic analysis and for continuous monitoring of biochemical processes.

Angiotensin I↗
PubMed2004

Application of a microfluidic reaction system for CdSe nanocrystal preparation: their growth kinetics and photoluminescence analysis.

We used a microreactor for CdSe nanocrystal preparation and explored the effects of experimental conditions on the properties of the products. The particle growth kinetics and photoluminescence properties of the nanocrystals showed identical trends to previous reports, indicating the efficiency of the current method for analysis of rapid nanocrystal synthesis as well as industrial production of CdSe nanocrystals.

Journal Article↗
PubMed2004

Aggregation of bead-monolayers in flat microfluidic chambers - simulation by the model of porous media.

In this paper, we for the first time simulate the process of hydrodynamic bead aggregation in a flat micro-fluidic chamber by a porous-media model in an iterative routine. This allows us to optimize the chamber design of our recently developed experimental method to form periodical monolayers from the flow of bead suspension. Periodical monolayers are advantageous for parallel assay formats since they enhance the mechanical rigidity of the aggregated pattern. This is important to avoid a spatial rearrangement along various steps of a read-out procedure which would impair the correlation between measurements. Furthermore, the monolayer formation guarantees the individual optical accessibility of all probe beads. By modelling the monolayers with porous media, we can drastically reduce the degrees of freedom in a two-phase, multi-particle problem. This way, we are able to compute stationary hydrodynamic flow patterns in the chamber. In order to simulate the complete filling process from these stationary solutions, we developed an iterative master routine which takes the transient aggregation pattern as the initial condition, then evaluates the placement of the newly introduced beads, and finally converts the points of aggregation into porous media.

Journal Article↗
PubMed2004

Correlation between the fluorescent response of microfluidity probes and the water content and viscosity of ionic liquid and water mixtures.

Accurate data on transport properties such as viscosity are essential in plant and process design involving ionic liquids. In this study, we determined the absolute viscosity of the ionic liquid + water system at water mole fractions from 0 to 0.25 for three 1-alkyl-3-methylimidazolium ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide and 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide. In each case, the excimer to monomer ratio for 1,m-bis(1-pyrenyl)alkanes (m= 3 or 10) was found to increase linearly with the mole fraction of water. Of the probes studied only PRODAN and rhodamine 6G, both of which have the ability to participate in hydrogen bonding, exhibited Perrin hydrodynamic behavior in the lower viscosity bis(trifluoromethane sulfonyl)imides. As a result, these probes allow for the extrapolation of the absolute viscosity of the ionic liquid mixture from the experimental fluorescence steady-state polarization values.

Journal Article↗
PubMed2004

Separation of lipids from blood utilizing ultrasonic standing waves in microfluidic channels.

A method to continuously separate different particle types in a suspension is reported. Acoustic forces in a standing wave field were utilized to discriminate lipid particles from erythrocytes in whole blood. The presented technology proposes a new method of cleaning, i.e. removing lipid emboli from, shed blood recovered during cardiac surgery. Blood contaminated with lipid particles enter a laminar flow micro channel. Erythrocytes and lipid particles suspended in blood plasma are exposed to a half wavelength standing wave field orthogonal to the direction of flow as they pass through the channel. Because of differences in compressibility and density the two particle types move in different directions, the erythrocytes towards the centre of the channel and the lipid particles towards the side walls. The end of the channel is split into three outlet channels conducting the erythrocytes to the centre outlet and the lipid particles to the side outlets due to the laminar flow profile. The separation channel was evaluated in vitro using polyamide spheres suspended in water, showing separation efficiencies approaching 100%. The system was also evaluated on whole blood using tritium labelled lipid particles added to bovine blood. More than 80% of the lipid particles could be removed while approximately 70% of the erythrocytes were collected in one third of the original fluid volume. The study showed that the further reduced micro channel dimensions provided improved performance with respect to; (i) separation efficiency, (ii) actuation voltage, and (iii) volumetric throughput as compared to earlier work.

Acoustics↗
PubMed2006

Multiphase microfluidics: from flow characteristics to chemical and materials synthesis.

We review transport characteristics of pressure-driven, multiphase flows through microchannel networks tens of nanometres to several hundred of micrometres wide with emphasis on conditions resulting in enhanced mixing and reduced axial dispersion. Dimensionless scaling parameters useful in characterizing multiphase flows are summarized along with experimental flow visualization techniques. Static and dynamic stability considerations are also included along with methods for stabilizing multiphase flows through surface modifications. Observed gas-liquid and immiscible liquid-liquid flows are summarized in terms of flow regime diagrams and the different flows are related to applications in chemistry and materials synthesis. Means to completely separate multiphase flows on the microscale and guidelines for design of scalable multiphase systems are also discussed.

Journal Article↗
PubMed2005

A lattice Boltzmann algorithm for electro-osmotic flows in microfluidic devices.

In this paper, a finite-difference-based lattice Boltzmann (LB) algorithm is proposed to simulate electro-osmotic flows (EOF) with the effect of Joule heating. This new algorithm enables a nonuniform mesh to be adapted, which is desirable for handling the extremely thin electrical double layer in EOF. The LB algorithm has been validated by simulating a problem with an available analytical solution and it is found that the numerical results predicted by the algorithm are in good agreement with the analytical solution. The LB algorithm is also applied to modeling a mixed electro-osmotic/pressure driven flow in a channel. The numerical results show that Joule heating plays an important role in EOF.

Journal Article↗
PubMed2006

Modeling electroosmotic and pressure-driven flows in porous microfluidic devices: zeta potential and porosity changes near the channel walls.

This work presents analytical solutions for both pressure-driven and electroosmotic flows in microchannels incorporating porous media. Solutions are based on a volume-averaged flow model using a scaling of the Navier-Stokes equations for fluid flow. The general model allows analysis of fluid flow in channels with porous regions bordering open regions and includes viscous forces, permitting consideration of porosity and zeta potential variations near channel walls. To obtain analytical solutions problems are constrained to the linearized Poisson-Boltzmann equation and a variation of Brinkman's equation [Appl. Sci. Res., Sect. A 1, 27 (1947); 1, 81 (1947)]. Cases include one continuous porous medium, two adjacent regions of different porosities, or one open channel adjacent to a porous region, and the porous material may have a different zeta potential than that of the channel walls. Solutions are described for two geometries, including flow between two parallel plates or in a cylinder. The model illustrates the relative importance of porosity and zeta potential in different regions of each channel.

Journal Article↗
PubMed2007

A trap-and-release integrated microfluidic system for dynamic microarray applications.

Dynamic microarrays hold great promise for advancing research in proteomics, diagnostics and drug discovery. However, this potential has yet to be fully realized due to the lack of reliable multifunctional platforms to transport and immobilize particles, infuse reagents, observe the reaction, and retrieve selected particles. We achieved all these functions in a single integrated device through the combination of hydrodynamic and optical approaches. Hydrodynamic forces allow simultaneous transportation and immobilization of large number of particles, whereas optical-based microbubble technique for bead retrieval gives dexterity in handling individual particles without complicated circuitry. Based on the criterion derived in this paper, the device was designed, and fabricated using standard photolithography and soft lithography methods. We examined the dynamics of bubble formation and dissipation in the device, and parametric studies revealed that higher power settings at short intervals were more efficient than low power settings at longer intervals for bead retrieval. We also demonstrated the capabilities of our device and its potential as a tool for screening methods such as the "one-bead-one-compound" (OBOC) combinatorial library method. Although both approaches, hydrodynamic confinement and optical-based microbubbles, are presented in one device, they can also be separately used for other applications in microchip devices.

Journal Article↗
PubMed2003

A microfluidic model for single-cell capillary obstruction by Plasmodium falciparum-infected erythrocytes.

Severe malaria by Plasmodium falciparum is a potentially fatal disease, frequently unresponsive to even the most aggressive treatments. Host organ failure is associated with acquired rigidity of infected red blood cells and capillary blockage. In vitro techniques have played an important role in modeling cell deformability. Although, historically they have either been applied to bulk cell populations or to measure single physical parameters of individual cells. In this article, we demonstrate the unique abilities and benefits of elastomeric microchannels to characterize complex behaviors of single cells, under flow, in multicellular capillary blockages. Channels of 8-, 6-, 4-, and 2-microm widths were readily traversed by the 8 microm-wide, highly elastic, uninfected red blood cells, as well as by infected cells in the early ring stages. Trophozoite stages failed to freely traverse 2- to 4-microm channels; some that passed through the 4-microm channels emerged from constricted space with deformations whose shape-recovery could be observed in real time. In 2-microm channels, trophozoites mimicked "pitting," a normal process in the body where spleen beds remove parasites without destroying the red cell. Schizont forms failed to traverse even 6-microm channels and rapidly formed a capillary blockage. Interestingly, individual uninfected red blood cells readily squeezed through the blockages formed by immobile schizonts in a 6-microm capillary. The last observation can explain the high parasitemia in a growing capillary blockage and the well known benefits of early blood transfusion in severe malaria.

Animals↗
PubMed2006

Laser manipulation in liquid crystals: an approach to microfluidics and micromachines.

Laser trapping of particles in three dimensions can occur as a result of the refraction of strongly focused light through micrometre-sized particles. The use of this effect to produce laser tweezers is extremely common in fields such as biology, but it is only relatively recently that the technique has been applied to liquid crystals (LCs). The possibilities are exciting: droplets of LCs can be trapped, moved and rotated in an isotropic fluid medium, or both particles and defects can be trapped and manipulated within a liquid crystalline medium. This paper considers both the possibilities. The mechanism of transfer of optical angular momentum from circularly polarized light to small droplets of nematic LCs is described. Further, it is shown that droplets of chiral LCs can be made to rotate when illuminated with linearly polarized light and possible mechanisms are discussed. The trapping and manipulation of micrometre-sized particles in an aligned LC medium is used to provide a measure of local shear viscosity coefficients and a unique test of theory at low Ericksen number in LCs.

Journal Article↗