Chong Liu

Dalian University of Technology, Lü-ta-shih, Liaoning, China

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Publications (74)132.9 Total impact

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    ABSTRACT: Glutamic-pyruvic transaminase (GPT) is one of the most important enzymes in human liver and has a valuable clinical reference for the diagnosis of many liver diseases. Here a method for the determination of GPT activity based on transdeamination is presented. In this method, a three electrode setup was used for the cyclic voltammetric determination of the enzyme. With the electrochemical detection of reduced nicotinamide adenine dinucleotide (NADH) produced from transdeamination, the GPT activity was characterized under optimal circumstances. Firstly, to verify the response of the electrode to NADH, a series of NADH concentrations varying from 39 μM to 2.5 mM were calibrated with cyclic voltammetry (CV). A linear relationship between the NADH concentration and the peak current with R2 0.9999 was obtained. Then the concentration of α-ketoglutarate (α-KG) which can exert great influence on transdeamination was also optimized and the most sensitive response was achieved at the point of 0.75 mM α-KG. Finally, the GPT activity was determined using both the unmodified screen-printed carbon electrode (SPCE) and the electrode modified with CNTs. The results showed that the relationship between the GPT activity and the peak current of the CV curve was linear between 60 U L−1 and 300 U L−1 and the modified electrode exhibited a slightly better linear relationship than the unmodified electrode. This work proposes a new enzymatic reactive system based on transdeamination for the electrochemical detection of GPT activity and combines the electrochemical detection of NADH with the determination of GPT activity.
    Analytical methods 10/2015; 7(22). DOI:10.1039/C5AY01794G · 1.82 Impact Factor

  • Micromachines 07/2015; 6(7):855-864. DOI:10.3390/mi6070855 · 1.27 Impact Factor
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    ABSTRACT: A microfluidic chip with integrated microelectrodes for real-time dopamine (DA) detection was designed and fabricated. The chip consisted of a polydimethylsiloxane (PDMS) channel plate and a glass electrode plate. One central channel as the culture chamber of neural stem cells and two lateral channels for the transportation of the culture medium were integrated on the PDMS channel plate. Microelectrodes for real-time dopamine detection were integrated on the glass electrode plate. To solve the problem in demoulding the PDMS channel plate from the silicon mold, a novel demoulding method was developed. An Au-Au-Au three-electrode system was constructed, and it performed well in electrochemical detection. The performance of the microfluidic chip was primarily studied by detecting dopamine dissolved in the medium for the culture of neural stem cells. The detection limit of dopamine was 3.92 μM, the linear detection range was from 10 μM to 500 μM, and the detection reproducibility from different chips was less than 4%. Copyright © 2015, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.
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    ABSTRACT: A novel method based on plasma etching was proposed for monolithically integrating planar nanochannels and microelectrodes on a poly (methyl methacrylate) (PMMA) plate, and complete PMMA nanofluidic electrochemical chips with integrated microelectrodes were constructed by bonding with another PMMA plate containing microchannels. The fabrication sequences of nanochannels and microelectrodes were optimized. The oxygen plasma etching rate of PMMA nanochannels was studied, and the average rate was 15nm/min under optimal conditions. An UV-ozone assisted thermal bonding method was developed to realize a low-temperature chip bonding, and the variations in width and depth of nanochannels before and after bonding were 2% and 5%, respectively. As a demonstration, a nanoparticle crystal (NPC)-based nanofluidic biosensor with integrated Ag microelectrodes was designed and fabricated. Sub-microchannel arrays with a depth of 400nm and a width of 30μm on the biosensor functioned as filters, and trapped 540nm silica nanoparticles modified with streptavidin inside the connected microchannel to assemble the NPC. The interspaces in the NPC formed a three-dimensional nanochannel network with an equivalent diameter of 81nm. By measuring the conductance across the NPC, a high quality nanofluidic sensing of biotin was achieved. The limit of detection was 1aM, and the detection range was from 1aM to 0.1nM. Copyright © 2015 Elsevier B.V. All rights reserved.
    Biosensors & Bioelectronics 05/2015; 72. DOI:10.1016/j.bios.2015.05.031 · 6.41 Impact Factor
  • Lu Gan · Chong Liu · Jing Min Li · Ya Hui Ma · Li Jie Zhou · Hao Zhang · Tao Li · Lei Wang ·
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    ABSTRACT: Microfluidic time gates are applied to control accurate flow time of liquids in the autonomous capillary systems, which are critical structures for point-of-care diagnostic and analytical applications. The time gate employs several abruptly changing geometry of the flow path to change the wettability of micro-channels to meet the requirement of delaying flow. However, obtaining desirable flow of liquids in microfluidics is still a limiting factor in the practical implementation. The work demonstrates a novel 2D serial cross-channel time gate and 3D serial cross-channel time gate. They are fabricated in PDMS-based autonomous capillary system. 2D serial cross-channel time gate is comprised of multiple paralleled channels of changeable width with dimensions from 300-800Îm. The number of the channels and the width variation of the cross intersections are crucial factors to influence the flow velocity of liquids. Compared with the 2D serial cross-channel time gate, the 3-D structures can eliminate the problem of entrapping air and improve the flow velocity of liquids in the time gate. The controlling time of the flow in 3D serial cross-channel time gate and 2D serial cross-channel time gate are 9~13s and 5s~51s, respectively.
    Key Engineering Materials 05/2015; 645-646:730-735. DOI:10.4028/ · 0.19 Impact Factor
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    ABSTRACT: In this work, a quaternized polysulfone/PTFE/H3PO4 composite membrane was prepared and used to a high temperature sustainable proton exchange membrane (HTPEM). This HTPEM was prepared based on a porous PTFE membrane, which can sustainable for 200 °C. Pt/C nano-suspension was prepared and deposited layer-by-layer on the gas diffusion layer (GDL) using electrohydrodynamic atomization (EHDA) deposition technique for the formation of cathode and anode catalyst layers (CLs). The CLs presented well packed and porous features. This EHDA deposited cathode and anode CLs, GDL and HTPEM were assembled to a membrane electrode assembly (MEA) and high temperature methanol fuel cell (HTMFC). The results showed that low concentration and high flow rate of methanol aqueous solution led to the loss of phosphoric acid on HTPEM, which resulted in the decline of the HTPEM. When the concentration and the flow rate of the methanol aqueous solution was increased and reduced, respectively, the cell can work properly at a temperature of 170 °C.
    Key Engineering Materials 05/2015; 645-646:1175-1180. DOI:10.4028/ · 0.19 Impact Factor
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    ABSTRACT: A catalyst-coated membrane (CCM) with structure and material gradient variation was deposited layer-by-layer (LbL) using electrohydrodynamic atomization (EHDA) deposition. This CCM contained 7 layers which is C cathode diffusion layer, Pt/C-C cathode transition layer, Pt/C cathode catalyst layer, Nafion membrane, Pt-Ru/C anode catalyst layer, Pt-Ru/C-C anode transition layer and C anode diffusion layer. The cathode and anode side were named as cathode and anode catalyst-diffusion layers, respectively. It was observed that the cathode and anode catalyst-diffusion layers presented the dendritic structure. Within the cathode and anode catalyst-diffusion layers, the Pt/C-C and Pt-Ru/C-C transition layer was more porous compared to the C layer, Pt/C layer and Pt-Ru/C layer. It was also shown that the EHDA LbL deposited CCM still presented close-packed structure after life test.
    Key Engineering Materials 05/2015; 645-646:1156-1162. DOI:10.4028/ · 0.19 Impact Factor
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    ABSTRACT: Silicon insert is a promising tool for microinjection moulding (MIM). However, its fracture problem induced by impact in MIM creates a bottleneck for application. The purpose of this paper is to investigate the impact behaviour in MIM and the effect on the fracture of silicon inserts. The finite element method is utilised to calculate the crack propagation of silicon inserts with pressure load and thermal load in the MIM process. The simulation result shows that the crack propagation is more easily induced by the increase of pressure load, while the temperature change has little effect on the crack propagation. An experimental platform, including a novel rotatable insert mould, is developed to investigate the dynamic pressure in the MIM process. The result shows that both the maximum pressure and the maximum loading rate occur in the initial period of MIM process. It indicates that the silicon insert is more prone to fracture at the beginning of the MIM process, and spatial pressure peaks are observed in the cavity as well. The nearly consistent distribution between the peak positions and the insert fracture zones shows that the pressure distribution is quite relevant to the fracture of the silicon insert. The result is helpful because it reveals the fracture phenomenon of silicon inserts.
    AIP Advances 04/2015; 5(4):041317. DOI:10.1063/1.4905950 · 1.52 Impact Factor
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    ABSTRACT: In this paper, a method of electrokinetic concentrating and a glass nanofluidic device for sensitivity-enhancing of magnetic beads-based antigen-antibody immunoassay (MBAAI) are presented. In the nanofluidic device, a polyacrylamide gel plug is deployed as the nanopores via photopolymerization reaction. To verify the capability of electrokinetic concentrating, the fluorescein isothiocyanate-bovine serum albumin (FITC-BSA) with initial concentration of 0.002 ng/ml is enriched and the concentration factor of a hundred million fold is achieved. And then the technique is implemented to improve the MBAAI sensitivity. In this experiment, magnetic beads coupled with sheep anti-rabbit IgG (immunoglobulin G) are firstly trapped into the immunoassay region via magnetic force, then the FITC-labeled rabbit IgG is electrokinetically concentrated and spontaneously bonded with the previous fixed magnetic beads. After the incubation, the total fluorescence intensity in immunoassay region is calculated. The result shows that the fluorescence intensity is improved by 58 % and the antigen-concentrating with the nanofluidic device can effectively enhance the sensitivity of MBAAI.
    Microsystem Technologies 01/2015; DOI:10.1007/s00542-015-2428-4 · 0.88 Impact Factor
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    ABSTRACT: An external-integrated biomimetic micropump for a microfluidic system is demonstrated. An "artificial leaf" is constituted, which mimics the stomatal transpiration process in plants and utilizes the negative pressure generated to drive the fluid flow. The biomimetic micropump integrated an SU-8 film with a micropore array, agarose gel, a flow rate control unit, and additional necessary operating auxiliaries. SU-8 film with micropores and agarose gel is used to mimic the stomata and the mesophyll cells in a leaf, respectively. The flow rate control unit can change the flow rate of the micropump by adjusting the number of micropores that participate in transpiration. Additional necessary operating auxiliaries can fix a microchip, provide a continuous fluid supply, and speed up the fluid flow rate. Experiments on a microchip are conducted to evaluate the performance of the micropump platform. Results have shown that the flow rate of the micropump can be increased by accelerating the wind speed or raising the temperature. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
    Journal of Micro/ Nanolithography, MEMS, and MOEMS 07/2014; 13(3):033008. DOI:10.1117/1.JMM.13.3.033008 · 1.43 Impact Factor
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    ABSTRACT: A novel method for fabricating a three-layer SU-8 mould with inverted T-shaped cavities is presented. The first two SU-8 layers were spin coated and exposed separately, and simultaneously developed to fabricate the bottom and the horizontal part of the inverted T-shaped cavity. Then, a positive photoresist was filled into the cavity, and a wet lapping process was performed to remove the excess photoresist and make a temporary substrate. The third SU-8 layer was spin coated on the temporary substrate to make the vertical part of the inverted T-shaped cavity. The sacrificial photoresist layer can prevent the first two SU-8 layers from being secondly exposed, and make a temporary substrate for the third SU-8 layer at the same time. Moreover, the photoresist can be easily removed with the development of the third SU-8 layer. A polydimethylsiloxane (PDMS) microchip with arrays of T-shaped cantilevers for studying the mechanics of cells was fabricated by using the SU-8 mould.
    Biomedical Microdevices 05/2014; 16(5). DOI:10.1007/s10544-014-9868-y · 2.88 Impact Factor
  • Ligeng Shao · Liqun Du · Chong Liu · Liding Wang ·
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    ABSTRACT: Nanocrystalline nickel was produced by pulse reverse microelectroforming. The pulse microelectroforming was also performed for the comparative purposes. The surface morphology and microstructure of electroformed nickel layers were investigated by scanning electron microscopy and X-ray diffractometry. The microhardness of nickel layers was measured with a Vickers microhardness tester. The friction and wear experiments for nickel layers were performed on a friction and wear tester. The results indicate that the nickel layers prepared by pulse reverse microelectroforming exhibit higher density and their grain sizes in the nanometer range. The nickel layers with fine grains, high microhardness and better wear resistance are obtained at positive current density of 20 A/dm2 and negative current density of 2 A/dm2. The microhardness and wear resistance of nickel layers are improved as the positive and negative current densities are increased.
    Journal of Experimental Nanoscience 03/2014; 9(3). DOI:10.1080/17458080.2012.660547 · 0.98 Impact Factor
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    ABSTRACT: Temperature drift error usually exists in the strain-temperature measurement of continuous welded rail (CWR) temperature force. A piece of invar with low (close to zero) coefficient of thermal expansion is used to simulate the actual CWR. Then the temperature drift of the strain sensor node is measured by using a programmable temperature chamber. The temperature drift error is compensated during the monitoring of the temperature force in actual CWR. Results show that the measured temperature force vibration of the CWR is-681kN~149kN and the stress-free temperature vibration is-2.4~1.0°Cwithin a month after temperature drift error compensation. The temperature force and stress-free temperature after compensation meets the stability condition of the CWR.
    03/2014; 541-542:1370-1375. DOI:10.4028/
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    ABSTRACT: A method for fabricating SU-8 moulds on glass substrates is presented. A common thin negative photoresist was coated on the glass slide as an adhesive layer, and then SU-8 was patterned on the adhesive layer. The presence of the adhesive layer improved the lifetime of a SU-8 mould from a few cycles to over 50 cycles. Moreover, the fabrication of the adhesive layer is quite simple and no additional equipment is required. The effects of the adhesion behavior of the negative photoresist and SU-8 on substrates on the durability of the SU-8 mould were investigated. The work of adhesion of the common thin negative photoresist on glass was 51.2 mJ m−2, which is 22.5% higher than that of SU-8 on silicon and 32.3% higher than that of SU-8 on glass. The abilities of the method for replicating high-aspect-ratio microstructures were also tested. One SU-8 mould with 60 × 60 array micropillars with aspect ratios lower than 3 could be used to cast at least 20 polydimethylsiloxane devices.
    Journal of Micromechanics and Microengineering 02/2014; 24(3):035009. DOI:10.1088/0960-1317/24/3/035009 · 1.73 Impact Factor
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    ABSTRACT: A new method for fabrication of micro-nanofluidic devices through photopolymerization was developed and related experimental research on trace enrichment was undertaken. COMSOL software was utilized to calculate and analyze the gel photopolymerization process on microscale. Moreover, a mathematical model of photopolymerization including photoinitiator decomposition, radical consumption, polymerization, etc., was established and the influence of the exposure time and the light intensity on gel nanosieve width was obtained. With an inverted fluorescence microscope, the micro-nanofluidic chip was prepared by integrating pore density-tunable gel nanosieves into specific areas of the microchannels through focusing, beam splitting and other control means. Based on the Poisson-Nernst-Planck model, the process of nanofluid-based electrokinetic enrichment process was simulated numerically, and the relationship between nanopore density and concentration ratio was investigated. By utilizing the prepared chips, the experiments of nanofluid-based electrokinetic enrichment were performed and the enrichment ratio of fluorescein isothiocyanate (FITC) could reach 600-fold when the mass ratio of the monomer acrylamide to the crosslinker N,N'-methylenebisacrylamide is 9:1.
    Chinese Journal of Analytical Chemistry 02/2014; 42(2):166–172. DOI:10.1016/S1872-2040(13)60707-0 · 0.75 Impact Factor
  • Chong Liu · Lei Wang · Jingmin Li · Meng Li · Yajie Duan · Tao Li · Lu Gan ·
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    ABSTRACT: A modified biomimetic micropump based on the stomatal transpiration principle is presented. The micropump is designed to have a layer of SU-8 microporous membrane and a layer of hydrophilic microporous ceramics, which reflects the natural plant stomata and mesophyll cells. The evaporation characteristics of the different stomata are analysed qualitatively by an established model. There is a positive connection between the stomata evaporation flux and the micropump flow rate. Corresponding experiments on micropump flow rate are conducted. The presented micropump has favourable assembly and reuse properties. The results indicate that the water vapour distribution in the stomata has a trend of edge effect. It also shows that the fluid flow rate in the micropump changes regularly with the stomata size and spacing.
    Micro & Nano Letters 01/2014; 9(1):41-45. DOI:10.1049/mnl.2013.0554 · 0.85 Impact Factor
  • Jun-yao Wang · Chong Liu · Zheng Xu · Yong-kui Li · Yun-liang Liu ·
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    ABSTRACT: In this paper, we present a new approach for ion-enrichment and ion-depletion effect (IEID) in micro-nanofluidic chips without external power source. The method utilizes different reducibility of various electrodes in the weak oxidizing solution to generate the electrochemical potential and then induce IEID at a micro-nano junction. The results show that the average gray values of the micro-nano junction based on Al–Pt, Fe–Pt, and Cu–Pt electrodes increase from 14.7 to 40.2, 27.1, 15.0 after 20 s, and electric currents for Al–Pt, Fe–Pt, and Cu–Pt electrodes are 5.0, 2.9 and 0 nA respectively. Metal cations generating from oxidation–reduction reaction and electroosmotic convection flow are evaluated and their influences to IEID can be neglected in this case. The IEID method based on the electrochemical potential is power-free and weak flow convective that will be beneficial to the integrity of micro-nanofluidic chips and stability of IEID.
    Microsystem Technologies 01/2014; 20(1). DOI:10.1007/s00542-013-1887-8 · 0.88 Impact Factor
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    ABSTRACT: A novel equivalent circuit model of capacitively coupled contactless conductivity detection (C4D) on microfluidic chips is presented. The impedance of the solution in microchannels facing the two electrodes for C4D was first introduced in the model of C4D on microfluidic chips. The electrodes and the solution facing electrodes were divided into individual segments in the model, and the effect of the length of divided segments on the model was studied. A back-calculating method was put forward to calculate the stray capacitance between the electrodes, and the variation between the calculated value and the simulated value was only 6 %. To evaluate the accuracy of the model, a hybrid poly (methyl methacrylate) (PMMA)/polydimethylsiloxane (PDMS) microchip was fabricated and a simple model was built. Compared with the outputs of the simple model, the data predicted by the novel model show a much closer fit to experimental results, and the variations were within 8 % over a wide concentration range of 1–500 μm for potassium chloride.
    Microsystem Technologies 12/2013; 19(12). DOI:10.1007/s00542-013-1736-9 · 0.88 Impact Factor
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    ABSTRACT: We present a new method to fabricate one-dimensional (1D) nanochannels on a thermoplastic substrate. This method has two main steps. First, a mold with microscale features is used to replicate microchannels on a thermoplastic substrate. Second, the fabricated microchannel is compressed to a 1D nanochannel at a temperature above the glass transition temperature (Tg) of the themoplastics. The effects of compression temperature, compression pressure, retaining time and loading rate on microchannel compression have been studied. Results have shown that a 1D nanochannel of 1–30 μm wide and 200–300 nm deep can be readily fabricated by using this method.
    Microsystem Technologies 11/2013; 19(11). DOI:10.1007/s00542-012-1733-4 · 0.88 Impact Factor
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    ABSTRACT: In this paper, the nanopore density effect on ion enrichment is quantitatively described with the ratio between electrophoresis flux and electroosmotic flow flux based on the Poisson-Nernst-Planck equations. A polyacrylamide gel plug is integrated into a microchannel to form a micro-nanofluidic chip. With the chip, electrokinetic ion enrichment is relatively stable and enrichment ratio of fluorescein isothiocyanate can increase to 600-fold within 120 s at the electric voltage of 300 V. Both theoretical research and experiments show that enrichment ratio can be improved through increasing nanopore density. The result will be beneficial to the design of micro-nanofluidic chips.
    Applied Physics Letters 07/2013; 103(4). DOI:10.1063/1.4816342 · 3.30 Impact Factor