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At least 649 records · Page 36Linked to original sources
PubMed2003

Numerical calculation of the electroosmotic flow at the cross region in microfluidic chips.

A numerical study is presented for the electroosmotic flow (EOF) at the cross region in microfluidic chips. The distributions of the electric potential due to the electric double layer (EDL) and the external electric field are discussed and the calculation of the latter can give rough speculations on the flow tendencies in the channels during various operation modes. Simplification of the two-dimensional Navier-Stokes (N-S) equations is obtained by focusing on the solution of interior flows, and the numerical calculation results show good agreement with the experimental images. The sample leakage to the separation channel during the "float" sampling proved to be caused not only by the sample diffusion, but also by the weak extension of the sampling electric field. It is also verified that with suitable voltage configuration, the "pinch" sampling mode is better than the "float" mode in sample plug control.

Electrophoresis, Capillary↗
PubMed2004

Microfluidic devices obtained by thermal toner transferring on glass substrate.

A new process for the manufacture of microfluidic devices based on deposition of laser-printing toner on glass substrates is described. It is an alternative method to the toner on polyester film (toner-polyester) one, previously introduced. Commercial laser printers cannot print directly on glass, thus the toner must first be printed on a special paper and then transferred by heating under pressure to the glass surface. Although this procedure is more complex than the toner-polyester one, it can be repeated several times, yielding multiple toner layers. Even without special alignment equipment, up to four layers could be satisfactorily piled up. Characterization tests revealed that the toner-glass devices have similar behavior as toner-polyester ones regarding the toner layer porosity. The main advantages of the toner-glass technology are improved mechanical stability, possibility of multiple toner layers, augmented electroosmotic flow (EOF), and improved heat transfer. On the other hand, toner adhesion to glass is weaker than to polyester, which limits the device lifetime and usable liquid media. The measured EOF mobility (3.5 x 10(-4) cm2.V(-1).s(-1) for pH 7) suggests that it is mainly determined by the glass surface, being little influenced by the toner walls. Microchip electrophoresis with contactless conductivity detection and photometric detection were implemented using toner-glass devices.

Electrophoresis, Microchip↗
PubMed2005

Experimental study and numerical estimation of current changes in electroosmotically pumped microfluidic devices.

Electroosmotic flow (EOF) was investigated in microfabricated fluidic devices using the current monitoring technique. Current changes ranging from 50 to 130 pA/s were detected. These observations indicate that in microfluidic devices with small reservoir volumes, electrolysis of water influences the fluid transport, giving rise to changes in pH and increase in concentration of ionic species in the fluidic system. As a result of the electrolysis and associated increment in ion concentration, the thickness of the Debye layer and surface potential vary, affecting the overall migration behavior of the solution. The magnitude of EOF and the electrophoretic properties of molecules can no longer be treated as constant/invariant. These temporal anomalies are undesirable during analytical separations and in fluid control applications. A numerical analysis of the impact of the continuous ionic strength increase on the EOF dynamics is presented using well-established conduction and EOF theories. The numerical results are found to be in good agreement with the observed current changes. These results indicate that to improve assay reproducibility, monitoring the electric current is an effective tool to determine whether electrolytic reactions are taking place. Our work also serves to test the numerical accuracy of EOF theories and models.

Electric Conductivity↗
PubMed2005

A rejuvenation method for poly(N,N-dimethylacrylamide)-coated glass microfluidic chips.

As microfluidic chips come to integrate the higher levels of functionality required for the implementation of advanced bioanalytical protocols, a crucial factor is that of cost. Although glass chips provide advantages in multilayer integrations, their cost is far higher than that of polymer chips. However, a simple and effective rejuvenation protocol for glass microchips may enable higher levels of integration and functionality on glass microchips. Here we present a method to rejuvenate glass microchips that had been used for capillary electrophoresis to the extent that their performance was degraded. This degradation was due to one of the two mechanisms: (i) a deterioration of the polymer coating on the inner surface of the microchannel or (ii) an aging of the glass substrate. Using the method presented here, we have rejuvenated more than 50 such "aged" microchips. The performance of these microchips was fully restored after the rejuvenation and lasted for hundreds of DNA separation runs. Our experiments indicate that the loss of resolution in microchip separations was not associated with glass aging, but was due to the degradation of the polymer coating on the inner surface of microchannels. This suggests that it is possible to extend the microchip lifetime "forever" using the rejuvenation protocol and that the exploration of higher levels of integration and functionality on glass microchips (or of hybrid structures involving materials capable of withstanding the reagents and elevated temperatures used) is feasible.

Acrylamides↗
PubMed2005

Fast immobilization of probe beads by dielectrophoresis-controlled adhesion in a versatile microfluidic platform for affinity assay.

The use of probe beads for lab-on-chip affinity assays is very interesting from a practical point of view. It is easier to handle and trap beads than molecules in microfluidic systems. We present a method for the immobilization of probe beads at defined areas on a chip using dielectrophoresis (DEP)-controlled adhesion. The method is fast, i.e., it takes between 10 and 120 s--depending on the protocol--to functionalize a chip surface at defined areas. The method is versatile, i.e., it works for beads with different types of probe molecule coatings. The immobilization is irreversible, i.e., the retained beads are able to withstand high flow velocities in a flow-through device even after the DEP voltage is turned off, thus allowing the use of conventional high-conductivity analyte buffers in the following assay procedure. We demonstrate the on-chip immobilization of fluorescent beads coated with biotin, protein A, and goat-antimouse immunoglobulin G (IgG). The number of immobilized beads at an electrode array can be determined from their fluorescence signal. Further, we use this method to demonstrate the detection of streptavidin and mouse IgG. Finally, we demonstrate the feasibility of the parallel detection of different analyte molecules on the same chip.

Animals↗
PubMed2006

Effects of separation length and voltage on isoelectric focusing in a plastic microfluidic device.

This paper describes the investigation on the effects of separation length and voltage on IEF in a plastic microfluidic device. A LIF, whole-channel imaging detection (WCID) system was developed to monitor proteins while they were moving under an electric field. IEF was carried out in a separation medium consisting of carrier ampholytes and a mixture of linear polymers (hydroxyethylcellulose and hydroxypropylcellulose). We found that the IEF separation resolution is essentially independent of separation length when the same voltage is applied, which agrees with the theory. This result supports the notion that IEF in a microfabricated device leads to more rapid analysis without sacrificing the resolving power. A higher separation voltage also brought about more rapid analysis and superior separation resolution. IEF of two proteins (green fluorescence protein and R-phycoerythrin) was achieved in 1.5 min when 500 V was applied across a 1.9-cm channel. We found that a linear relationship exists between the focusing time and the inverse of the electrical field strength. In addition, we confirmed the phenomenon in which the pH gradient was compressed to the middle of a channel, and we found that the relative amount of the gradient compression decreased with the channel length.

Electricity↗
PubMed2006

Automated screening using microfluidic chip-based PCR and product detection to assess risk of BK virus-associated nephropathy in renal transplant recipients.

The cost-effective detection of viral particles in bodily fluids could enable more effective responses to viral outbreaks, whether isolated clinical cases, or influenza epidemics. In renal transplant recipients, complications arising from high levels of BK virus can lead to graft dysfunction, graft loss, and/or reduced patient survival. We describe a microfluidic system for the sensitive analysis of BK virus (viral load) in unprocessed urine samples that are applied directly onto the chip, thus avoiding labor-intensive processing and sources of inter-assay variability. Integration of small volume genetic amplification (PCR) and electrophoretic analysis detects as few as 1-2 viral copies, distinguishes between high, medium and low levels of virus and reliably identifies viral loads requiring clinical intervention. As a first step to wider application in the clinic and in the field, the present work presents an entirely microchip-based system, validated against conventional clinical methods using clinical samples.

BK Virus↗
PubMed2006

A microfluidic-based system for analysis of single cells based on Ca2+ flux.

A microfluidic format-based system has been developed for in situ monitoring of the calcium flux response to agonists using Chinese hamster ovary (CHO) cells. The assay is based on measuring the fluorescent intensity of the calcium-sensitive indicator, Fluo-4 AM, and was performed in a modified glass chip channel, whose surface was functionalised using a silanisation method with 3-aminopropyltriethoxysilane (APTS) (enabling the cells to be immobilised on the channel surface). CHO cells calcium flux response was measured for different agonists over a range of concentrations. Cells and reagents were introduced into the chip in a continuous flow as a series of plugs in a given sequence.

Aniline Compounds↗
PubMedDate not supplied

Optimisation of polymeric surface pre-treatment to prevent bacterial biofilm formation for use in microfluidics.

The production of a microfluidic device for microbial culture has necessitated the development of techniques for the prevention of bacterial adhesion to a range of polymeric substrates including fluoropolymers such as fluorinated ethylene polypropylene, and polyolefins such as low-density polyethylene. Treatment of such materials to increase hydrophilicity reduces the incidence of attachment of Escherichia coli during the first 4 h of cultivation, although no decrease in the number of biofilm initiation sites was detected after 16 h. The incorporation of a mannose analogue to block binding proteins on the F1 binding fimbriae was also investigated. The possibility of ensuring suspension culture of bacterial cells in high surface area to volume ratio nano-vessels is thus facilitated by the correct choice and pre-treatment of materials used in their construction.

Bacterial Adhesion↗
PubMed2006

Surface engineering of microchannel walls for protein separation and directed microfluidic flow.

The preparation of surfaces in microfluidic devices that selectively retain proteins may be difficult to implement due to the incompatibility of derivatization methods with microdevice fabrication techniques. This review describes recently reported developments in simple and rapid methods for engineering the surface chemistries of microchannels based on construction of press-fit microdevices. These devices are fabricated by placing a glass fiber on a PDMS film and pressing the film on a silicon wafer or a microscope slide that has been derivatized with octadecyltrichlorosilane (ODS). The film adheres to the slide and forms an elliptically shaped channel around the fiber. The combination of surface wettability of a hydrophilic glass microfiber and the surrounding hydrophobic microchannel surfaces directs a narrow boundary layer of liquid next to the fiber in order to bring the sample in contact with the separation media and results in selective retention of proteins. This phenomenon may be exploited to enable microscale separation applications since there are a wide variety of fibers available with different chemistries. These may be used to rapidly fabricate microchannels that serve as stationary phases for separation at a microscale. The fundamental properties of such devices are discussed.

Electrophoresis, Microchip↗
PubMed2006

Fungi use efficient algorithms for the exploration of microfluidic networks.

Fungi, in particular, basidiomycetous fungi, are very successful in colonizing microconfined mazelike networks (for example, soil, wood, leaf litter, plant and animal tissues), a fact suggesting that they may be efficient solving agents of geometrical problems. We therefore evaluated the growth behavior and optimality of fungal space-searching algorithms in microfluidic mazes and networks. First, we found that fungal growth behavior was indeed strongly modulated by the geometry of microconfinement. Second, the fungus used a complex growth and space-searching strategy comprising two algorithmic subsets: 1) long-range directional memory of individual hyphae and 2) inducement of branching by physical obstruction. Third, stochastic simulations using experimentally measured parameters showed that this strategy maximizes both survival and biomass homogeneity in microconfined networks and produces optimal results only when both algorithms are synergistically used. This study suggests that even simple microorganisms have developed adequate strategies to solve nontrivial geometrical problems.

Algorithms↗
PubMed2003

A microfluidic biosensor based on nucleic acid sequence recognition.

The development of a generic semi-disposable microfluidic biosensor for the highly sensitive detection of pathogens via their nucleic acid sequences is presented in this paper. Disposable microchannels with defined areas for capture and detection of target pathogen RNA sequence were created in polydimethylsiloxane (PDMS) and mounted onto a reusable polymethylmethacrylate (PMMA) stand. Two different DNA probes complementary to unique sequences on the target pathogen RNA serve as the biorecognition elements. For signal generation and amplification, one probe is coupled to dye encapsulated liposomes while the second probe is coupled to superparamagnetic beads for target immobilization. The probes hybridize to target RNA and the liposome-target-bead complex is subsequently captured on a magnet. The amount of liposomes captured correlates directly to the concentration of target sequence and is quantified using a fluorescence microscope. Dengue fever virus serotype 3 sequences and probes were used as a model analyte system to test the sensor. Probe binding and target capture conditions were optimized for sensitivity resulting in a detection limit of as little as 10 amol microL(-1) (10 pmol L(-1)). Future biosensors will be designed to incorporate a mixer and substitute the fluorescence detection with an electrochemical detection technique to provide a truly portable microbiosensor system.

Base Sequence↗
PubMed2005

High benzene selectivity of mesoporous silicate for BTX gas sensing microfluidic devices.

The gas selectivities of highly ordered mesoporous silicates and commercially-obtained porous silicates with respect to benzene, toluene and xylene were studied. After studying the porosities, pore uniformities, and surface silanol structures of the silicates and their relationships to gas selectivity in detail, we found that we could achieve high benzene selectivity by controlling the micropore size (less than 1 nm). Concluding that mesoporous silicate has a suitable micropore size and structure for benzene selectivity, we also observed that mesoporous silicate SBA-16 exhibited a high (>6) benzene selectivity from toluene and xylene even in a pseudo-atmospheric environment. A benzene detection limit of about 100 ppb was achieved by introducing SBA-16 into a microfluidic device originally developed for the separate detection of benzene, toluene, and xylene gases.

Air Pollutants, Occupational↗
PubMed2005

Single-molecule fluorescence detection in microfluidic channels--the Holy Grail in muTAS?

Both single-molecule detection (SMD) methods and miniaturization technologies have developed very rapidly over the last ten years. By merging these two techniques, it may be possible to achieve the optimal requirements for the analysis and manipulation of samples on a single molecule scale. While miniaturized structures and channels provide the interface required to handle small particles and molecules, SMD permits the discovery, localization, counting and identification of compounds. Widespread applications, across various bioscience/analytical science fields, such as DNA-analysis, cytometry and drug screening, are envisaged. In this review, the unique benefits of single fluorescent molecule detection in microfluidic channels are presented. Recent and possible future applications are discussed.

Biosensing Techniques↗
PubMed2005

Determination of reactive oxygen species in single human erythrocytes using microfluidic chip electrophoresis.

Reactive oxygen species (ROS) are known to not only mediate the damage of cellular constituents but also to regulate cellular signaling. Analysis of ROS is essential if we wish to understand the mechanisms of cellular alterations. In this paper, a microfluidic chip-based approach to the determination of ROS in single erythrocyte was developed by using a simple crossed-channel glass chip with integrated operational functions, including cell sampling, single cell loading, docking, lysing, and capillary electrophoretic (CE) separation with laser-induced fluorescence (LIF) detection. Non-fluorescent dihydrorhodamine 123 (DHR 123), which can be oxidized intracellularly by ROS to the fluorescent rhodamine 123 (Rh 123), was used as the fluorogenic reagent. The effect of pH on the migration time of Rh 123 and detection sensitivity was discussed. The present method minimized dilution of intracellular ROS during reaction with DHR 123 and determination. As a result, an extremely low detection limit of 0.8 amol has been achieved. The time required for complete analysis of one human erythrocyte was less than 3 min. A migration time precision of 4.1% RSD was obtained for six consecutively-injected cells. Upon stimulation with 4 mmol/l H2O2 for 10 min, the intracellular ROS concentration was found to increase on average by about a factor of 8.4.

Calibration↗
PubMed2005

Neutrophil migration in opposing chemoattractant gradients using microfluidic chemotaxis devices.

Neutrophils migrating in tissue respond to complex overlapping signals generated by a variety of chemotactic factors (CFs). Previous studies suggested a hierarchy between bacteria-derived CFs and host-derived CFs but could not differentiate neutrophil response to potentially equal host-derived CFs (IL-8 and LTB4). This paper reports neutrophil migration in conflicting gradients of IL-8 and LTB4 using a microfluidic chemotaxis device that can generate stable and well-defined gradients. We quantitatively characterized the movement of cells from time-lapse images. Neutrophils migrate more efficiently toward single IL-8 gradients than single LTB4 gradients as measured by the effective chemotactic index (ECI). In opposing gradients of IL-8 and LTB4, neutrophils show obvious chemotaxis toward a distant gradient, consistent with previous reports. When an opposing gradient of LTB4 is present, neutrophils show less effective chemotaxis toward IL-8 than when they are in a gradient of IL-8 alone. In contrast, the chemotactic response of neutrophils to LTB4 is not reduced in opposing gradients as compared to that in a single LTB4 gradient. These results indicate that the presence of one host-derived CF modifies the response of neutrophils to a second CF suggesting a subtle hierarchy between them.

Cell Culture Techniques↗
PubMed2005

Microreactor microfluidic systems with human microsomes and hepatocytes for use in metabolite studies.

In the area of drug discovery, high-speed synthesis has increased the number of drug candidates produced. These potential drugs need to be evaluated for their adsorption, distribution, metabolism, elimination, and toxicology (ADMET) properties as early in the drug development stage as possible. Previously, a potential drug's ADMET properties have been found out by using monolayer cell cultures and live animals. These methods can be costly, time-intensive, and impractical for screening the large amount of potential drugs created by combinatorial chemistry. A quick, small, inexpensive, and highly parallel device would be desirable to determine a drug candidate's properties (i.e., metabolism of the drug). Here we fabricate a microfluidic device entrapping human microsomes within poly(ethylene) glycol hydrogels thereby generating an in situ microreactor to assess a drug candidate's metabolic properties that can be coupled to analysis equipment. We show that microsomes can be entrapped without the loss of enzymatic activity during photopolymerization. Additionally, a microreactor utilizing hepatocytes was also created for comparison with the microsome microreactor.

Biological Assay↗