Microfluidic Chip (microfluidic + chip)

Distribution by Scientific Domains

Kinds of Microfluidic Chip

  • glass hybrid microfluidic chip
  • hybrid microfluidic chip


  • Selected Abstracts


    Sol-gel-derived Poly(dimethylsiloxane) Enzymatic Reactor for Microfluidic Peptide Mapping

    CHINESE JOURNAL OF CHEMISTRY, Issue 7 2006
    Hui-Ling Wu
    Abstract The silica-based poly(dimethylsiloxane) (PDMS) microfluidic enzymatic reactor was reported along with its analytical features in coupling with MALDI TOF and ESI MS. Microfluidic chip was fabricated using PDMS casting and O2 -plasma techniques, and used for the preparation of enzymatic reactor. Plasma oxidation for PDMS enabled the channel wall of microfluidics to present a layer of silanol (SiOH) groups. These SiOH groups as anchors onto the microchannel wall were linked covalently with the hydroxy groups of trypsin-encapsulated sol matrix. As a result, the leakage of sol-gel matrix from the microchannel was effectively prevented. On-line protein analysis was performed with the microfluidic enzymatic reactor by attachment of stainless steel tubing electrode and replaceable tip. The success of trypsin encapsulation was investigated by capillary electrophoresis (CE) detection, and MALDI TOF and ESI MS analysis. The lab-made device provided excellent extent of digestion even at the fast flow rate of 7.0 (L/min with very short residence time of ca. 2 s. In addition, the encapsulated trypsin exhibits increased stability even after continuous use. These features are the most requisite for high-throughput protein identification. [source]


    Dynamic coating of SU-8 microfluidic chips with phospholipid disks

    ELECTROPHORESIS, Issue 15 2010
    Tiina Sikanen
    Abstract In this work, PEG-stabilized phosphatidylcholine lipid aggregates (disks), mimicking mammalian cell membranes, were introduced as a new biofouling resistant coating for SU-8 polymer microchannels. A rapid and simple method was developed for immobilization of PEGylated phosphatidylcholine disks in microchannels. Microfluidic chips made from SU-8, PDMS, or glass were dynamically coated with the PEGylated disks followed by characterization of their surface chemistry before and after coating. On the basis of the observed changes in EOF and nonspecific protein adsorption, the affinity of the PEGylated disks was shown to be particularly strong toward SU-8. The PEG-lipid coating enabled permanent change in EOF in SU-8 microchannels with an initial value of 4.5×10,8,m2,V,1,s,1, decreasing to 2.1×10,8,m2,V,1,s,1 (immediately after modification), and, eventually, to 1.5×10,8,m2,V,1,s,1 (7 days after modification) for 9,mM sodium borate (pH 10.5) as BGE. As determined by the Wilhelmy plate measurements and microchip-CE analysis of BSA, the PEG-lipid coating also enabled efficient biofouling shield against protein adsorption, similar to that of low amounts of SDS (3.5,mM) or Tween-20 (80,,M) as buffer additives. These results suggest that dynamically attached PEG-lipid aggregates provide stable, biomimicking surface modification that efficiently reduces biofouling on SU-8. [source]


    Microfluidic chips for mass spectrometry-based proteomics

    JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2009
    Jeonghoon Lee
    Abstract Microfluidic devices coupled to mass spectrometers have emerged as excellent tools for solving the complex analytical challenges associated with the field of proteomics. Current proteome identification procedures are accomplished through a series of steps that require many hours of labor-intensive work. Microfluidics can play an important role in proteomic sample preparation steps prior to mass spectral identification such as sample cleanup, digestion, and separations due to its ability to handle small sample quantities with the potential for high-throughput parallel analysis. To utilize microfluidic devices for proteomic analysis, an efficient interface between the microchip and the mass spectrometer is required. This tutorial provides an overview of the technologies and applications of microfluidic chips coupled to mass spectrometry for proteome analysis. Various approaches for combining microfluidic devices with electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) are summarized and applications of chip-based separations and digestion technologies to proteomic analysis are presented. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    Electrochemical Detection of Anions on an Electrophoresis Microchip with Integrated Silver Electrode

    ELECTROANALYSIS, Issue 13 2005
    Jilin Yan
    Abstract A poly(dimethylsiloxane)/glass hybrid microfluidic chip with integrated silver electrode is described for electrochemical detection of anions. The working electrode was directly fabricated on a glass slide and the chip formed by reversibly sealing of a PDMS slab with microchannels to the slide. Under an alkaline phosphate condition, thiocyanide and three halides were sensitively detected. Factors influencing the separation and detection procedure were discussed and optimized. Linear responses over two magnitudes were obtained with limit of detection at the micromolar level. [source]


    Cover Picture: Electrophoresis 20'2009

    ELECTROPHORESIS, Issue 20 2009
    Article first published online: 27 OCT 200
    Issue no. 20 is a regular issue with an Emphasis on "Fundamentals and Methodologies". The bulk of this issue (13 articles) is on fundamentals and methodologies covering various topics, e.g. EOF, affinity CE, structural analysis of glycosphingolipids by CE-ESI-MS, on-line concentration, monolithic columns, etc. The other 6 articles are on protein separation and proteomics. Selected articles are: Micropump based on electroosmosis of the second kind ((10.1002/elps.200900271)) A splicing model-based DNA computing approach on microfluidic chip ((10.1002/elps.200900323)) Proteomic Characterization of Plasma-derived Clotting Factor VIII , von Willebrand Factor Concentrates ((10.1002/elps.200900270)) [source]


    Red blood cell quantification microfluidic chip using polyelectrolytic gel electrodes

    ELECTROPHORESIS, Issue 9 2009
    Kwang Bok Kim
    Abstract This paper reports on a novel microfluidic chip with polyelectrolytic gel electrodes (PGEs) used to rapidly count the number of red blood cells (RBCs) in diluted whole blood. The proposed microdevice is based on the principle that the impedance across a microchannel between two PGEs varies sensitively as RBCs pass through it. The number and amplitude of impedance peaks provide the information about the number and size of RBCs, respectively. This system features a low-voltage dc detection method and non-contact condition between cells and metal electrodes. Major advantages include stable detection under varying cellular flow rate and position in the microchannel, little chance of cell damage due to high electric field gradient and no surface fouling of the metal electrodes. The performance of this PGEs-based system was evaluated in three steps. First, in order to observe the size-only dependence of the impedance signal, three different sizes of fluorescent microbeads (7.2, 10.0, and 15.0,,m; Bangs laboratories, USA) were used in the experiment. Second, the cell counting performance was evaluated by using 7.2,,m fluorescent microbeads, similar in size to RBCs, in various concentrations and comparing the results with an animal hematoanalyzer (MS 9-5; Melet schloesing laboratories, France). Finally, in human blood sample tests, intravenously collected whole blood was just diluted in a PBS without centrifuge or other pretreatments. The PGE-based system produced almost identical number of RBCs in over 800-fold diluted samples to the results from a commercialized human hematoanalyzer (HST-N402XE; Sysmex, Japan). [source]


    IEF in microfluidic devices

    ELECTROPHORESIS, Issue 5 2009
    Greg J. Sommer
    Abstract IEF is one of the most powerful and prevalent techniques used in separation sciences. The power of IEF comes from the fact that it not only separates analytes based on their pI but also focuses them into highly resolved bands. In line with the miniaturization trend spurring the analytical community, the past decade has yielded a wealth of research focused on implementing IEF in microfluidic chip-based formats (,IEF). Scaling down the separation technique provides several advantages such as reduced sample sizes, assay automation, and significant improvements in assay speed without sacrificing separation performance. Besides presenting microscale adaptations of standard schemes, researchers have also developed improved detection techniques, demonstrated novel ,IEF assays, and incorporated ,IEF with other analytical methods for achieving on-chip multidimensional separations. This review provides a brief historical outline of IEF's beginnings, theoretical incentives driving miniaturization of the methodology, a thorough synopsis of ,IEF publications to date, and an outlook to the future. [source]


    Cover Picture: Electrophoresis 4'09

    ELECTROPHORESIS, Issue 4 2009
    Article first published online: 26 FEB 200
    Issue no. 4 is a special issue on "CEC and EKC" containing 20 papers including 2 Fast Track papers. The first Fast Track paper deals with high-resolution computer simulations of EKC while the second Fast Track paper reports the use of camera cell phone to detect the gold nanoparticle-labeled immunoassay results on microfluidic chip. The remaining 18 papers of this special issue are distributed into four parts. Part I is on monolithic capillaries for CEC and has five papers demonstrating the continuous efforts in developing novel monolithic stationary phases. Part II, which assembles six contributions, is on various aspects of MEKC separations of a wide range of compounds in the presence of different types of micelles. On-line concentration cum EKC/CEC is the subject of Part III that has five contributions demonstrating signal enhancement for various small and large molecules. This issue concludes with Part IV on enantioseparations by chiral EKC and CEC. [source]


    On-chip tryptic digest with direct coupling to ESI-MS using magnetic particles

    ELECTROPHORESIS, Issue 24 2008
    Anne Le Nel
    Abstract As a step toward a fully automated front-end microfluidic chip for MS proteomics, we propose a system capable of performing online tryptic digest and ESI-MS, using a replaceable on-chip digestion microcolumn based on self-assembled magnetic particles. [source]


    Temperature gradient focusing in a PDMS/glass hybrid microfluidic chip

    ELECTROPHORESIS, Issue 24 2007
    Takuya Matsui
    Abstract This paper reports the application of temperature gradient focusing (TGF) in a PDMS/glass hybrid microfluidic chip. With TGF, by the combination of a temperature gradient along a microchannel, an applied electric field, and a buffer with a temperature-dependent ionic strength, analytes are focused by balancing their electrophoretic velocities against the bulk velocity of the buffer containing the analytes. In this work, Oregon Green 488 carboxylic acid was concentrated approximately 30 times as high as the initial concentration in 45,s at moderate electric strength of 70,V/cm and a temperature gradient of 55°C across the PDMS/glass hybrid microfluidic chip with a 1,cm long capillary. [source]


    Electrophoresis on a microfluidic chip for analysis of fluorescence-labeled human rhinovirus

    ELECTROPHORESIS, Issue 24 2007
    Viliam Kolivo
    Abstract We report the analysis of human rhinovirus serotype 2 (HRV2) on a commercially available lab-on-a-chip instrument. Due to lack of sufficient native fluorescence, the proteinaceous capsid of HRV2 was labeled with Cy5 for detection by the red laser (,ex 630,nm) implemented in the instrument. On the microdevice, electrophoresis of the labeled virus was possible in a BGE without stabilizing detergents, which is in contrast to conventional CE; moreover, analysis times were drastically shortened to the few 10,s range. Resolution of the sample constituents (virions, a contaminant present in all virus preparations, and excess dye) was improved upon adaptation of the separation conditions, mainly by adjusting the SDS concentration of the BGE. Purity of fractions from size-exclusion chromatography after labeling of virus was assessed, and affinity complex formation of the labeled virus with various recombinant very-low-density lipoprotein receptor derivatives differing in the number of concatenated V3 ligand binding repeats was monitored. Virus analysis on microchip devices is of particular interest for experiments with infectious material because of easy containment and disposal of samples. Thus, the employment of microchip devices in routine analysis of viruses appears to be exceptionally attractive. [source]


    Microchip capillary electrophoresis with a cellulose-DNA-modified screen-printed electrode for the analysis of neurotransmitters

    ELECTROPHORESIS, Issue 15 2005
    Muhammad Johirul
    Abstract A microfluidic chip based on capillary electrophoresis coupled with a cellulose-single-stranded DNA (cellulose-ssDNA) modified electrode was used for the simultaneous analysis of dopamine (DA), norepinephrine (NE), 3,4-dihydroxy- L -phenylalanine (L -DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), and ascorbic acid (AA). The modification of the electrode improved the electrophoretic analysis performance by lowering the detection potential and enhancing the signal-to-noise characteristic without surface poisoning of the electrode. The sensitivity of the modified electrode was about 12 times higher than those of the bare ones. The test compounds were separated using a 62,mm long separation channel at the separation field strength of +200,V/cm within 220,s in a 10,mM phosphate buffer (pH,7.4). The most favorable potential for the amperometric detection was 0.7,V (vs. Ag/AgCl). A reproducible response (relative standard deviation of 1.3, 1.3, 2.1, 3.1, 3.4% for DA, NE, L -DOPA, DOPAC, and AA, respectively, for n,=,9) for repetitive sample injections reflected the negligible electrode fouling at the cellulose-ssDNA modified electrode. Square-wave voltammetric analyses reflected the sensitivities of the modified electrode for DA, NE, L -DOPA, DOPAC, and AA which were 1.78, 0.82, 0.69, 2.45, and 1.23,nC/µM with detection limits of 0.032, 0.93, 1.13, 0.31, and 0.62,µM, respectively. The applicability of this microsystem to real sample analysis was demonstrated. [source]


    Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometry

    ELECTROPHORESIS, Issue 11 2005
    Feng Li
    Abstract This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg·L,1 Hg(II) and 4 mg·L,1 MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 µg·L,1 (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%. [source]


    High-resolution DNA separation in microcapillary electrophoresis chips utilizing double-L injection techniques

    ELECTROPHORESIS, Issue 21-22 2004
    Lung-Ming Fu
    Abstract An experimental and numerical investigation into the use of high-resolution injection techniques to separate DNA fragments within electrophoresis microchips is presented. The principal material transport mechanisms of electrokinetic migration, fluid flow, and diffusion are considered, and several variable-volume injection methods are discussed. A detailed analysis is provided of a double-L injection technique, which employs appropriate electrokinetic manipulations to reduce sample leakage within the microchip. The leakage effect in electroosmotic flow (EOF) is investigated using a sample composed of rhodamine B and Cy3 dye. Meanwhile, the effects of sample leakage in capillary electrophoresis (CE) separation are studied by considering the separation of 100-base pairs (bp) DNA ladders and HaeIII-digested ,X-174 DNA samples. The present experimental and simulation results indicate that the unique injection system employed in the current microfluidic chip has the ability to replicate the functions of both the conventional cross-channel and the shift-channel injection systems. Furthermore, applying the double-L injection method to these two injection systems is shown to reduce sample leakage significantly. The proposed microfluidic chip and double-L injection technique developed in this study have an exciting potential for use in high-resolution, high-throughput biochemical analysis applications and in many other applications throughout the micrototal analysis systems field. [source]


    Enzyme-catalyzed amperometric oxidation of neurotransmitters in chip-capillary electrophoresis

    ELECTROPHORESIS, Issue 12 2004
    Maria A. Schwarz
    Abstract The determination of biogenic monoamines by enzyme-catalyzed oxidation after electrophoretical separation on a microfluidic chip decreases their detection limits significantly. An amperometric system with a chemically amplified response for neurotransmitters and their metabolites is presented. The principle is the rapid cyclic oxidation of the analyte on the amperometric detector in the presence of the redoxactive enzyme glucose oxidase in the capillary electrophoresis buffer. With this approach, detection limits in the range of 10,7,10,8M could be reached. Because of the good linearity between the current response and the concentration of catecholamines and their metabolites at concentrations up to 300 ,M, this method is attractive for the analytical detection at low concentration levels such as in biological fluids. [source]


    Microfluidic device for capillary electrochromatography-mass spectrometry

    ELECTROPHORESIS, Issue 21 2003
    Iulia M. Lazar
    Abstract A novel microfabricated device that integrates a monolithic polymeric separation channel, an injector, and an interface for electrospray ionization-mass spectrometry detection (ESI-MS) was devised. Microfluidic propulsion was accomplished using electrically driven fluid flows. The methacrylate-based monolithic separation medium was prepared by photopolymerization and had a positively derivatized surface to ensure electroosmotic flow (EOF) generation for separation of analytes in a capillary electrochromatography (CEC) format. The injector operation was optimized to perform under conditions of nonuniform EOF within the microfluidic channels. The ESI interface allowed hours of stable operation at the flow rates generated by the monolithic column. The dimensions of one processing line were sufficiently small to enable the integration of 4,8 channel multiplexed structures on a single substrate. Standard protein digests were utilized to evaluate the performance of this microfluidic chip. Low- or sub-fmol amounts were injected and detected with this arrangement. [source]


    Analysis of chicken and turkey ovalbumins by microchip electrophoresis combined with exoglycosidase digestion

    ELECTROPHORESIS, Issue 18 2003
    Xiuli Mao
    Abstract The polypeptide and carbohydrate patterns of two glycoproteins, chicken ovalbumin (CO) and turkey ovalbumin (TO), were analyzed by microchip electrophoresis (ME), following digestion with proteases and exoglycosidases. Glycopeptides derived from ovalbumin were obtained by digestion with Pronase, followed by dialysis, and then separated by ME. Using CO as model, the method was developed to deduce the structure of glycans from glycoproteins by comparing the electropherograms of glycopeptides with and without digestion of exolycosidases. Applying the same approach, the structure of oligosaccharides linked to TO was determined. TO was found to contain high-mannose type oligosaccharides and oligosaccharides with terminal N -acetylglucosamine residues. The complete primary analysis of CO and TO by ME described in this paper provides a basis for an analysis of glycoproteins with an integrated microfluidic chip. [source]


    Capturing Complex Protein Gradients on Biomimetic Hydrogels for Cell-Based Assays

    ADVANCED FUNCTIONAL MATERIALS, Issue 21 2009
    Steffen Cosson
    Abstract A versatile strategy to rapidly immobilize complex gradients of virtually any desired protein on soft poly(ethylene glycol) (PEG) hydrogel surfaces that are reminiscent of natural extracellular matrices (ECM) is reported. A microfluidic chip is used to generate steady-state gradients of biotinylated or Fc-tagged fusion proteins that are captured and bound to the surface in less than 5,min by NeutrAvidin or ProteinA, displayed on the surface. The selectivity and orthogonality of the binding schemes enables the formation of parallel and orthogonal overlapping gradients of multiple proteins, which is not possible on conventional cell culture substrates. After patterning, the hydrogels are released from the microfluidic chip and used for cell culture. This novel platform is validated by conducting single-cell migration experiments using time-lapse microscopy. The orientation of cell migration, as well as the migration rate of primary human fibroblasts, depends on the concentration of an immobilized fibronectin fragment. This technique can be readily applied to other proteins to address a wealth of biological questions with different cell types. [source]


    Transient flow patterns in a microfluidic chip with a complicated microstructure

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2008
    Wei Zhang
    Abstract The transient flow patterns of the boiling flow in a microfluidic chip with a complicated microstructure were studied at low mass fluxes and high heat fluxes. The periodic flow pattern in the timescale of milliseconds and the stratified flow pattern were observed. For a specific separated zone, the liquid film thickness was increased along the flow direction and the dry-out always occurred earlier at the microchannel upstream rather than downstream. However, for different microchannel zones, the dry-out took place earlier in the downstream zone. It was determined that the low liquid Froude number was responsible for the formation of the stratified flow. The large boiling number resulted in a large shear stress at the vapor,liquid interface, leading to the accumulation of the liquid in the microchannel downstream, causing the increased liquid film thickness along the flow direction. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(4): 224,231, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20201 [source]


    Applicability of laser-induced Raman microscopy for in situ monitoring of imine formation in a glass microfluidic chip

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003
    Moonkwon Lee
    Abstract Laser-induced Raman microscopy has been used to illustrate its applicability for the in situ monitoring of imine formation reaction in a glass microfluidic chip. In order to monitor the diffusion process in a micro channel, the Raman spectra were measured at various points along the channel with a constant flow rate of 2.7 µl min,1. Time-dependent Raman spectra were also measured without flow in order to monitor the variation of Raman peaks to a complete conversion. The disappearance of the CO stretching peak at 1700 cm,1 of the reactant, benzaldehyde, and the appearance of the Raman peak for the product, an imine, at 1628 cm,1 were successfully monitored. In addition, the intensity increases of three phenyl stretching modes in the 1550,1630 cm,1 region were also observed. The increase in Raman intensity for this vibrational mode is caused by an effective ,-electron conjugation between two phenyl rings through the ,CN,bridging group of the product. Laser-induced Raman microscopy enables us to monitor in situ product formation and to obtain detailed structural information in a glass microfluidic chip. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Quantification of D -Asp and D -Glu in rat brain and human cerebrospinal fluid by microchip electrophoresis

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2009
    Yong Huang
    Abstract A microchip electrophoresis (MCE) method with LIF detection was presented for quantification of D -aspartic acid (D -Asp) and D -glutamate (D -Glu) in biological samples. D -Asp and D -Glu were determined after precolumn derivatization with FITC. The chiral separation was performed on a glass/PDMS hybrid microfluidic chip using ,-CD as chiral selector in the running buffer. High sensitive detection was obtained by the LIF detection. The LODs (S/N = 3) for D -Asp and D -Glu were 6.0×10,8 and 4.0×10,8 M, respectively. Using this method, the levels of D -Asp and D -Glu in rat brain and human cerebrospinal fluid (CSF) were determined. [source]


    A microfluidics approach for the isolation of nucleated red blood cells (NRBCs) from the peripheral blood of pregnant women

    PRENATAL DIAGNOSIS, Issue 10 2008
    R. Huang
    Abstract Objective Nucleated red blood cells (NRBCs) have been identified in maternal circulation and potentially provide a resource for the monitoring and diagnosis of maternal, fetal, and neonatal health and disease. Past strategies used to isolate and enrich for NRBCs are limited to complex approaches that result in low recovery and less than optimal cell purity. Here we report the development of a high-throughput and highly efficient microfluidic device for isolating rare NRBCs from maternal blood. Material and Methods NRBCs were isolated from the peripheral blood of 58 pregnant women using a microfluidic process that consists of a microfluidic chip for size-based cell separation and a magnetic device for hemoglobin-based cell isolation. Results The microfluidic,magnetic combination removes nontarget red blood cells and white blood cells at a very high efficiency (,99.99%). The device successfully identified NRBCs from the peripheral blood of 58/58 pretermination samples with a mean of 37.44 NRBC/mL (range 0.37,274.36 NRBC/mL). These results were compared with those from previous studies. Conclusion The microfluidic device results in an approximate 10- to 20-fold enrichment of NRBCs over methods described previously. The reliability of isolation and the purity of the NRBC product have the potential to enable the subsequent application of molecular diagnostic assays. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Synthesis and utilization of E. coli -encapsulated PEG-based microdroplet using a microfluidic chip for biological application

    BIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010
    Kyoung G. Lee
    Abstract We report herein an effective strategy for encapsulating Escherichia coli in polyethylene glycol diacrylate (PEGDA) microdroplets using a microfluidic device and chemical polymerization. PEGDA was employed as a reactant due to the biocompatibility, high porosity, and hydrophilic property. The uniform size and shape of microdroplets are obtained in a single-step process using microfluidic device. The size of microdroplets can be controlled through the changing continuous flow rate. The combination of microdroplet generation and chemical polymerization techniques provide unique environment to produce non-toxic ways of fabricating microorganism-encapsulated hydrogel microbeads. Due to these unique properties of micro-sized hydrogel microbeads, the encapsulated E. coli can maintain viability inside of microbeads and green fluorescent protein (GFP) and red fluorescent protein (RFP) genes are efficiently expressed inside of microbeads after isopropyl- , - D -thiogalactopyranoside induction, suggesting that there is no low-molecular weight substrate transfer limitation inside of microbeads. Furthermore, non-toxic, gentle, and outstanding biocompatibility of microbeads, the encapsulated E. coli can be used in various applications including biotransformation, biosensing, bioremediation, and engineering of artificial cells. Biotechnol. Bioeng. 2010;107:747,751. © 2010 Wiley Periodicals, Inc. [source]


    Microfluidic biolector,microfluidic bioprocess control in microtiter plates

    BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2010
    Matthias Funke
    Abstract In industrial-scale biotechnological processes, the active control of the pH-value combined with the controlled feeding of substrate solutions (fed-batch) is the standard strategy to cultivate both prokaryotic and eukaryotic cells. On the contrary, for small-scale cultivations, much simpler batch experiments with no process control are performed. This lack of process control often hinders researchers to scale-up and scale-down fermentation experiments, because the microbial metabolism and thereby the growth and production kinetics drastically changes depending on the cultivation strategy applied. While small-scale batches are typically performed highly parallel and in high throughput, large-scale cultivations demand sophisticated equipment for process control which is in most cases costly and difficult to handle. Currently, there is no technical system on the market that realizes simple process control in high throughput. The novel concept of a microfermentation system described in this work combines a fiber-optic online-monitoring device for microtiter plates (MTPs),the BioLector technology,together with microfluidic control of cultivation processes in volumes below 1,mL. In the microfluidic chip, a micropump is integrated to realize distinct substrate flow rates during fed-batch cultivation in microscale. Hence, a cultivation system with several distinct advantages could be established: (1) high information output on a microscale; (2) many experiments can be performed in parallel and be automated using MTPs; (3) this system is user-friendly and can easily be transferred to a disposable single-use system. This article elucidates this new concept and illustrates applications in fermentations of Escherichia coli under pH-controlled and fed-batch conditions in shaken MTPs. Biotechnol. Bioeng. 2010;107: 497,505. © 2010 Wiley Periodicals, Inc. [source]


    A spring-driven press device for hot embossing and thermal bonding of PMMA microfluidic chips

    ELECTROPHORESIS, Issue 15 2010
    Zhi Chen
    Abstract A novel spring-driven press device was designed and manufactured for hot embossing and thermal bonding of PMMA microfluidic chips in this work. This simple device consisted of two semi-cylinder silicone rubber press heads, three steel clamping plates, and three compression springs that were assembled together using two screw bolts and two butterfly nuts. The three springs were clamped between the upper and the middle clamping plates, whereas the two press heads were assembled between the middle and the lower clamping plates. After an epoxy template covered by a PMMA plate or a PMMA channel plate together with a cover were sandwiched between two microscopic glass slides for embossing or bonding, respectively, they were clamped between the two elastic press heads of the press device by fastening the screw nuts on the upper clamping plate. Because the convex press heads applied pressure along the middle line of the glass slides, they would deform resulting in a negative pressure gradient from the middle to the sides so that air bubbles between the sandwiched parts could be squeezed out during embossing and bonding processes. High-quality PMMA microfluidic chips were prepared by using this unique device and were successfully applied in the electrophoretic separation of several cations. [source]


    Dynamic coating of SU-8 microfluidic chips with phospholipid disks

    ELECTROPHORESIS, Issue 15 2010
    Tiina Sikanen
    Abstract In this work, PEG-stabilized phosphatidylcholine lipid aggregates (disks), mimicking mammalian cell membranes, were introduced as a new biofouling resistant coating for SU-8 polymer microchannels. A rapid and simple method was developed for immobilization of PEGylated phosphatidylcholine disks in microchannels. Microfluidic chips made from SU-8, PDMS, or glass were dynamically coated with the PEGylated disks followed by characterization of their surface chemistry before and after coating. On the basis of the observed changes in EOF and nonspecific protein adsorption, the affinity of the PEGylated disks was shown to be particularly strong toward SU-8. The PEG-lipid coating enabled permanent change in EOF in SU-8 microchannels with an initial value of 4.5×10,8,m2,V,1,s,1, decreasing to 2.1×10,8,m2,V,1,s,1 (immediately after modification), and, eventually, to 1.5×10,8,m2,V,1,s,1 (7 days after modification) for 9,mM sodium borate (pH 10.5) as BGE. As determined by the Wilhelmy plate measurements and microchip-CE analysis of BSA, the PEG-lipid coating also enabled efficient biofouling shield against protein adsorption, similar to that of low amounts of SDS (3.5,mM) or Tween-20 (80,,M) as buffer additives. These results suggest that dynamically attached PEG-lipid aggregates provide stable, biomimicking surface modification that efficiently reduces biofouling on SU-8. [source]


    A microfluidic study of mechanisms in the electrophoresis of supercoiled DNA

    ELECTROPHORESIS, Issue 12 2008
    Dammika P. Manage
    Abstract In this work, microfluidic chips were used to study the electrophoresis of supercoiled DNA (SC DNA) in agarose. This system allowed us to study the electrophoretic and trapping behaviours of SC DNA of various lengths, at various fields and separation distances. Near a critical electric field the DNA is trapped such that the concentration falls exponentially with distance. The trapping of such circular DNA has been explained in terms of the ,lobster trap' or ,impalement' model where shorter fibres become trapping sites at higher fields, leading to an ongoing (and gradual) increase in trapping with increasing field. By contrast, the present study suggests that under some circumstances the traps have a barrier such that only when the DNA has sufficient energy (at high enough fields) can it become trapped, leading to a sudden transition in behaviours at the critical field. We propose an ,activated impalement' mechanism of trapping in which only at sufficiently high fields is the SC DNA impaled and trapped for long times. The critical electric field appears to be inversely proportional to the length of the DNA molecule, suggesting that the force required to impale the SC DNA is constant. [source]


    Microchip-based small, dense low-density lipoproteins assay for coronary heart disease risk assessment

    ELECTROPHORESIS, Issue 9 2008
    Hua Wang
    Abstract Small, dense low-density lipoprotein (sdLDL) has been accepted as an emerging cardiovascular risk factor, and there has been an increasing interest in analytical methods for sdLDL profiling for diagnosis. Serum sdLDL may be measured by different laboratory techniques, but all these methods are laborious, time-consuming, and costly. Recently, we have demonstrated that a low-temperature bonding of quartz microfluidic chips for serum lipoproteins analysis (Zhuang, G., Jin, Q., Liu, J., Cong, H. et al., Biomed. Microdevices 2006, 8, 255,261). In contrast to this previous study, we chose SDS as anionic surfactant to modify both lipoproteins and the channel surface to minimize lipoprotein adsorption and improve the resolution of lipoprotein separation. Two major LDL subclass patterns including large, buoyant LDL (lLDL), sdLDL, and high-density lipoprotein (HDL) were effectively separated with high reproducibility. RSD values of the migration time (min) and peak areas of standard LDL and HDL were 6.28, 4.02, 5.02, and 2.5%, respectively. Serum lipoproteins of 15 healthy subjects and 15 patients with coronary heart disease (CHD) were separated by microchip CE. No peaks of sdLDL were detected in serum samples of healthy subjects while sdLDL fractional peaks were observed in patients' entire serum samples. These results suggested that the microchip-based sdLDLs assay was a simple, rapid, and highly efficient technique and significantly improved the analysis of CHD risk factors. [source]


    An optimized microchip electrophoresis system for mutation detection by tandem SSCP and heteroduplex analysis for p53,gene exons,5,9

    ELECTROPHORESIS, Issue 19 2006
    Christa N. Hestekin
    Abstract With the complete sequencing of the human genome, there is a growing need for rapid, highly sensitive genetic mutation detection methods suitable for clinical implementation. DNA-based diagnostics such as single-strand conformational polymorphism (SSCP) and heteroduplex analysis (HA) are commonly used in research laboratories to screen for mutations, but the slab gel electrophoresis (SGE) format is ill-suited for routine clinical use. The translation of these assays from SGE to microfluidic chips offers significant speed, cost, and sensitivity advantages; however, numerous parameters must be optimized to provide highly sensitive mutation detection. Here we present a methodical study of system parameters including polymer matrix, wall coating, analysis temperature, and electric field strengths on the effectiveness of mutation detection by tandem SSCP/HA for DNA samples from exons,5,9 of the p53 gene. The effects of polymer matrix concentration and average molar mass were studied for linear polyacrylamide (LPA) solutions. We determined that a matrix of 8%,w/v 600,kDa LPA provides the most reliable SSCP/HA mutation detection on chips. The inclusion of a small amount of the dynamic wall-coating polymer poly- N -hydroxyethylacrylamide in the matrix substantially improves the resolution of SSCP conformers and extends the coating lifetime. We investigated electrophoresis temperatures between 17 and 35°C and found that the lowest temperature accessible on our chip electrophoresis system gives the best condition for high sensitivity of the tandem SSCP/HA method, especially for the SSCP conformers. Finally, the use of electrical fields between 350 and 450,V/cm provided rapid separations (<10,min) with well-resolved DNA peaks for both SSCP and HA. [source]


    Study of Joule heating effects on temperature gradient in diverging microchannels for isoelectric focusing applications

    ELECTROPHORESIS, Issue 10 2006
    Brian Kates
    Abstract IEF is a high-resolution separation method taking place in a medium with continuous pH gradients, which can be set up by applying electrical field to the liquid in a diverging microchannel. The axial variation of the channel cross-sectional area will induce nonuniform Joule heating and set up temperature gradient, which will generate pH gradient when proper medium is used. In order to operationally control the thermally generated pH gradients, fundamental understanding of heat transfer phenomena in microfluidic chips with diverging microchannels must be improved. In this paper, two 3-D numerical models are presented to study heat transfer in diverging microchannels, with static and moving liquid, respectively. Through simulation, the temperature distribution for the entire chip has been revealed, including both liquid and solid regions. The model for the static liquid scenario has been compared with published results for validation. Parametric studies have showed that the channel geometry has significant effects on the peak temperature location, and the electrical conductivity of the medium and the wall boundary convection have effects on the generated temperature gradients and thus the generated pH gradients. The solution to the continuous flow model, where the medium convection is considered, shows that liquid convection has significant effects on temperature distribution and the peak temperature location. [source]