Zhi Chen

Fudan University, Shanghai, Shanghai Shi, China

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Publications (11)42.17 Total impact

  • Zhi Chen, Luyan Zhang, Gang Chen
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    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.
    Electrophoresis 08/2010; 31(15):2512-9. · 3.26 Impact Factor
  • Zhi Chen, Zhengyin Yu, Gang Chen
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    ABSTRACT: A simple method based on disposable gelatin gel templates has been developed for the low-cost fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Gelatin was dissolved in glycerol aqueous solution under heat to prepare a thermally reversible impression material. The molten gel was then sandwiched between a glass plate and a SU-8 template bearing negative relief of microstructure. After cooling, the negative SU-8 template could be easily separated from the solidified gelatin gel and a layer of gelatin template bearing positive relief of the microstructure was left on the glass plate. Subsequently, prepolymerized methyl methacrylate molding solution containing a UV-initiator was sandwiched between the gel template and a PMMA plate and was allowed to polymerize under UV light to fabricate PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers using plasticizer-assisted thermal bonding at 90 degrees C. Gelatin gel template can be mass-produced and will find application in the mass production of PMMA microchips at low cost. The prepared microfluidic microchips have been successfully employed in the capillary electrophoresis analysis of several ions in connection with contactless conductivity detection.
    Talanta 06/2010; 81(4-5):1325-30. · 3.50 Impact Factor
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    ABSTRACT: A simple method based on electric heating wires has been developed for the rapid fabrication of poly(methyl methacrylate) (PMMA) electrophoresis microchips in ordinary laboratories without the need for microfabrication facilities. A piece of stretched electric heating wire placed across the length of a PMMA plate along its midline was sandwiched between two microscope slides under pressure. Subsequently, alternating current was allowed to pass through the wire to generate heat to emboss a separation microchannel on the PMMA separation channel plate at room temperature. The injection channel was fabricated using the same procedure on a PMMA sheet that was perpendicular to the separation channel. The complete microchip was obtained by bonding the separation channel plate to the injection channel sheet, sealing the channels inside. The electric heating wires used in this work not only generated heat; they also served as templates for embossing the microchannels. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of ions in connection with contactless conductivity detection.
    Analytical and Bioanalytical Chemistry 02/2010; 396(7):2715-20. · 3.66 Impact Factor
  • Xiao Yao, Zhi Chen, Gang Chen
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    ABSTRACT: A novel method based on disposable agar hydrogel temples have been developed for the fabrication of PMMA microfluidic chips. Molten agar hydrogel was sandwiched between a glass plate and a PMMA template bearing negative relief of microstructure. After cooling, the negative PMMA template could be easily separated from the solidified agar hydrogel and a layer of agar hydrogel temple bearing high-fidelity positive relief of the microstructure was left on the glass plate. Prepolymerized methyl methacrylate molding solution containing ultraviolet-initiator was subsequently sandwiched between the agar hydrogel template and a PMMA plate and was allowed to polymerize under ultraviolet light to fabricate the PMMA channel plate at room temperature. Complete microchips could be obtained by bonding the channel plates with covers. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of several ions in connection with contactless conductivity detection.
    Electrophoresis 12/2009; 30(24):4225-9. · 3.26 Impact Factor
  • Zhi Chen, Luyan Zhang, Gang Chen
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    ABSTRACT: In this report, a novel carbon nanotube/poly(ethylene-co-vinyl acetate) (CNT/EVA) composite electrode was developed for the amperometric detection in CE. The composite electrode was fabricated by packing a mixture of CNTs and melted EVA in a piece of fused-silica capillary under heat. It was coupled with CE for the separation and detection of esculin and esculetin in Cortex Fraxini, a traditional Chinese medicine, to demonstrate its feasibility and performance. Esculin and esculetin have been well separated within 9 min in a 40 cm long capillary at a separation voltage of 12 kV using a 50 mM borate buffer (pH 9.2). The new CNT-based CE detector offered significantly lower detection potentials, yielded enhanced S/N characteristics, and exhibited high resistance to surface fouling and enhanced stability. It showed long-term stability and reproducibility with relative standard deviations of less than 5% for the peak current (n=15) and should also find a wide range of applications in other microfluidic analysis systems.
    Electrophoresis 10/2009; 30(19):3419-26. · 3.26 Impact Factor
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    ABSTRACT: This report describes the development and the application of a novel carbon-nanotube (CNT)-alginate composite modified electrode as a sensitive amperometric detector for capillary electrophoresis (CE). The composite electrode was fabricated on the basis of in situ gelation of a mixture of CNTs and sodium alginate on the surface of a carbon disc electrode in aqueous calcium chloride solution. SEM, energy-dispersive spectroscopy, XRD, and FTIR spectroscopy offered insights into the nature of the novel composite. The results indicated that the CNTs were well dispersed and embedded throughout the alginate matrix to form an interconnected carbon-nanotube network on the base electrode. The performance of this unique CNT-based detector has been demonstrated, in conjunction with CE, by separating and detecting five caffeic acid derivatives. The new CNT-based CE detector offered significantly lower operating potentials, substantially enhanced signal-to-noise characteristics, and a lower expense of operation. The simplicity and significant performance exhibited by the CNT-alginate composite modified electrode also indicate great promise for the use of this electrode in microchip CE, flowing-injection analysis, and other microfluidic analysis systems.
    Chemistry 10/2008; 14(31):9779-85. · 5.83 Impact Factor
  • Zhi Chen, Luyan Zhang, Gang Chen
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    ABSTRACT: A method based on capillary electrophoresis-amperometric detection has been developed for the determination of catechin, rutin, kaempferol, gentistic acid, and quercetin in Folium Eriobotryae with the aid of microwave-assisted solvent extraction. The effects of the acidity and the concentration of the running buffer, separation voltage, injection time, detection potential, and irradiation time were investigated to acquire the optimum analysis conditions. The detection electrode was a 300-mum-diameter carbon disc electrode at a detection potential of +0.90 V. The five analytes could be well separated within 12 min in a 40-cm length fused-silica capillary at a separation voltage of 12 kV in a 50-mM borate buffer (pH 9.0). The relation between peak current and analyte concentration was linear over about three orders of magnitude with detection limits (S/N=3) ranging from 2.1 to 4.5 microM for all the analytes.
    Journal of Chromatography A 07/2008; 1193(1-2):178-81. · 4.61 Impact Factor
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    ABSTRACT: In this report, a core-changeable needle enzymatic reactor was developed for highly efficient proteolysis. A piece of enzyme-immobilized fiber core was inserted into the needle of a syringe pump to form a flow-through bioreactor. The novel in-needle bioreactor could be regenerated by changing its fiber core. The feasibility and performance of the unique bioreactor were demonstrated by the tryptic digestion of BSA and lysozyme and the digestion time was significantly reduced to less than 5 s. The digests were identified by MALDI-TOF MS with sequence coverages comparable to those obtained by the conventional in-solution tryptic digestion. The present in-needle bioreactor provides a promising platform for the high-throughput protein identification.
    Proteomics 06/2008; 8(9):1785-8. · 4.43 Impact Factor
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    ABSTRACT: In this work, a piece of glass fiber was inserted into the channel of a poly(methyl methacrylate) (PMMA) electrophoresis microchip to enhance the electroosmotic flow (EOF) and the separation efficiency. The EOF value of the glass fiber-containing microchannel at pH 8.2 was determined to be 4.17 x 10(-4)cm2 V(-1)s(-1). The performance of the new microchip was demonstrated by its ability to separate and detect three purines coupled with end-column amperometric detection. In addition, a piece of trypsin-immobilized glass fiber was inserted into the channel of a PMMA microchip to fabricate a core-changeable microfluidic bioreactor that can be regenerated by changing the fiber. The in-channel fiber bioreactor has been coupled with matrix-assisted laser desorption ionization time-of-flight mass spectrometry for the digestion and peptide mapping of bovine serum albumin and myoglobin.
    Journal of Chromatography A 03/2008; 1179(2):224-8. · 4.61 Impact Factor
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    ABSTRACT: Capillary electrophoresis (CE) with amperometric detection (AD) has been developed for the separation and determination of disaccharide glycoside rutin, gentistic acid, quercetin, and gallic acid in the leaves of Ricinus communis Linn. for the first time. The effects of the acidity and the concentration of the running buffer, separation voltage, injection time, and detection potential were investigated to acquire the optimum conditions for the determination of the four analytes. The detection electrode was a 300microm diameter carbon disc electrode at a detection potential of +0.90V (versus saturated calomel electrode (SCE)). The four analytes could be well separated within 10min in a 40cm length fused silica capillary at a separation voltage of 15kV in a 50mM borate buffer (pH 9.0). The relation between peak current and analyte concentration was linear over about 3 orders of magnitude with detection limits (S/N=3) ranging from 0.8 to 2.9microM for all the analytes. The proposed method has been successfully applied to monitor flavones and phenolic acids in the real plant samples with satisfactory assay results.
    Journal of Chromatography B 03/2008; 863(1):101-6. · 2.49 Impact Factor
  • Zhi Chen, Luyan Zhang, Gang Chen
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    ABSTRACT: A method based on the in situ polymerization of methyl methacrylate (MMA) has been developed for the rapid fabrication of a novel separation platform, fiber electrophoresis microchip. To demonstrate the concept, prepolymerized MMA molding solution containing a UV initiator was sandwiched between a poly(methyl methacrylate) (PMMA) cover plate and a PMMA base plate bearing glycerol-permeated fiberglass bundles and was exposed to UV light. During the UV-initiated polymerization, the fiberglass bundles were embedded in the PMMA substrate to form fiberglass-packed microchannels. When the glycerol in the fiberglass bundles was flushed away with water, the obtained porous fiberglass-packed channels could be employed to perform electrophoresis separation. Scanning electron micrographs (SEMs) and microscopic images offered insights into the fiber electrophoresis microchip. The analytical performance of the novel microchip has been demonstrated by separating and detecting dopamine and catechol in connection with end-column amperometric detection. The fiber-based microchips can be fabricated by the new approach without the need for complicated and expensive lithography-based microfabrication techniques, indicating great promise for the low-cost production of microchips, and should find a wide range of applications.
    Electrophoresis 08/2007; 28(14):2466-73. · 3.26 Impact Factor