Chong Liu

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

Are you Chong Liu?

Claim your profile

Publications (63)122.39 Total impact

  • [Show abstract] [Hide abstract]
    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; · 2.72 Impact Factor
  • [Show abstract] [Hide abstract]
    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. · 1.73 Impact Factor
  • [Show abstract] [Hide abstract]
    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. · 0.79 Impact Factor
  • [Show abstract] [Hide abstract]
    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; · 0.95 Impact Factor
  • [Show abstract] [Hide abstract]
    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. · 0.80 Impact Factor
  • [Show abstract] [Hide abstract]
    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 01/2014; 9(3). · 1.04 Impact Factor
  • [Show abstract] [Hide abstract]
    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; · 0.95 Impact Factor
  • [Show abstract] [Hide abstract]
    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; · 0.95 Impact Factor
  • [Show abstract] [Hide abstract]
    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). · 3.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Monolithic integration of three-material microelectrodes for electrochemical detection on poly (methyl methacrylate) (PMMA) substrates is presented. Au–Ag–Pt three-material electrodes were all fabricated based on polymer compatible photolithography processes, and the fabrication sequence of the electrodes was optimized. The C–Ag–Pt three-electrode system was also demonstrated. To reduce the electrical resistance, the carbon electrode was made on a silver intermediate layer which was simultaneously fabricated with Ag electrodes. A PMMA/poly(dimethylsiloxane) electrochemical sensing microchip with the Au–Ag–Pt three-electrode systems was constructed. The reproducibility of the three-electrode system from single and different microchips was characterized. The performance of the microchip was evaluated by two kinds of electrochemical probes (Ru(bpy)3Cl2 and dopamine).
    Electrochemistry Communications 06/2013; 31:20–23. · 4.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, an integrated catalyst-coated membrane (CCM) is prepared by successively spray deposit Pt/C nano-suspension, Nafion solution and Pt–Ru/C nano-suspension on a cathode gas diffusion layer using electrohydrodynamic atomization (EHDA) Layer-by-Layer (LbL) deposition. Porous cathode and anode catalyst layers and dense Nafion membrane are deposited using the EHDA LbL deposition technique. It is also found that the EHDA LbL deposited CCM presents close packed structure. An 85 h life test shows that the EHDA LbL deposited cathode electrode side of the integrated CCM still presents well compact feature. Whereas, the delamination of the anode electrode side formed by direct pressing method is evident. The performance of the cell with different methanol concentrations is also examined. It is found that the 3 M methanol concentration gives the highest cell performance. Moreover, the polarization behaviour, methanol crossover and impedance response of the cell at different working temperatures are analysed. The cell performance demonstrates faster increase between 20 °C and 50 °C than between 50 °C and 70 °C. The methanol crossover test shows that the cell presents higher increase level of methanol crossover between 40 °C and 50 °C than other 10 °C temperature increase steps.
    Journal of Power Sources 02/2013; 224:202–210. · 5.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: “Reservoir unsealed” and “boundary layer separation” are two main issues in the fabrication of a multilayer poly(methyl methacrylate) (PMMA) microfluidic chip. In this paper, embedded sacrificial layer bonding (ESLB) and laser edge welding (LEW) are presented to avoid them. ESLB is performed by inserting a sacrificial-layer into a reservoir to enhance the transfer of bonding pressure among different layers. LEW is performed by using CO2 laser to weld the edge of a bonded multilayer chip. By using these two methods, a three-layer microchip and a five layer micro-mixer are fabricated. Our results demonstrated that ESLB and LEW can be implemented readily in the fabrication of a multilayer thermoplastic microfluidic chip which may facilitate the development of sophisticated microfluidic systems.
    Journal of Materials Processing Technology 11/2012; 212(11):2315–2320. · 2.04 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A polydimethylsiloxane (PDMS) electrophoresis microchip with a thickness-controllable insulating layer for capacitatively coupled contactless conductivity detection is presented. A PDMS film is spin-coated on a glass slide with Pt microelectrodes to be the insulating layer, and then permanently bonded with a PDMS channel plate to make the whole microchip. The thickness of PDMS films can be precisely controlled down to submicrometers. With a microchip with a 0.6 μm-thick PDMS insulating layer, a superior limit of detection (LOD) of 0.07 μM for Na+ was obtained. For comparison, another two microchips with the same design but different insulating layer thicknesses (15 μm and 50 μm) were tested, and LODs were 1 μM and 3 μM respectively, which are almost two orders of magnitude higher. Moreover, the microchip detector also exhibited excellent linearity, reproducibilities and separation efficiencies.
    Electrochemistry Communications 11/2012; 25:147–150. · 4.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: One method of fabricating micro/nanofluidic chips is to form microchannels and nanochannels in different plates and then assemble them together. In this paper, two practicable methods for the assembly of the micro/nanofluidic chips were built up. One was the rotating-then-pushing method (RP) and the other was the picking-up-then-placing-down method (PP). Only an inverted microscope and a few mechanical parts were needed. With the well-assembled chips, the experiments of enrichment and micro/nano-flow were conducted. Relevant devices, processes, and characteristics were presented in detail. These flexible assembly methods present the advantages such as low-cost, flexibility, and interchangeability.
    Microelectronic Engineering 09/2012; 97:1–7. · 1.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present a new approach that is capable of fabricating nanochannels in a poly(methyl methacrylate) (PMMA) substrate. This method, which we call microchannel refill (MR), utilizes the refilling of glassy thermoplastics under thermal compression to reduce a microscopic channel to a nanochannel. It only has two main steps. First, a microchannel is fabricated in a PMMA substrate using normal hot embossing. Second, the microchannel is compressed under a certain temperature and pressure to obtain a nanochannel. We show that a nanochannel with a width as small as 132 nm (with a depth of 85 nm) can be easily produced by choosing the appropriate compression temperature, compression pressure, original microchannel width and original microchannel aspect ratio. Compared with most current nanochannel fabrication methods, MR is a quick, simple and cost-effective way to produce nanochannels in polymer substrates.
    Lab on a Chip 08/2012; 12(20):4059-62. · 5.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To set up a point-of-care whole-blood immunoassay system, sample preparation and on-chip storage of conjugate reagents are indispensable functional units. Here, we merge these functions into a deposited microbead plug (DMBP) to simultaneously play the roles of a blood filter and a conjugate reagent carrier. The DMBP was easily fabricated by the use of natural deposition of beads without the need of weirs. Conjugate reagents (FITC labeled antibodies used here) were incorporated into the DMBP during the assembly of the DMBP. To demonstrate the ability of the DMBP, we constructed a DMBP-based microfluidic chip and used it for the detection of human IgG (hIgG). The DMBP enabled to remove blood cells from whole blood and provide the pure plasma for the downstream on-chip immunoreactions. The release of reconstituted FITC labeled antibodies from the DMBP was controlled in a passive fashion. Dry FITC labeled antibodies retained at least 81% of their activity after 60 days of storage at the room temperature. The DMBP presented here makes an important step towards the development of the self-contained, integrated, sample-to-answer microfluidic chips for point-of-care diagnostics.
    Talanta 08/2012; 97:376-81. · 3.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel macro-micro modeling method has been presented for designing three-dimensional microfluidic devices in system-level. The macro model was used to solve mass transfer in simple modules of a microfluidic device, such as straight channels. The micro model was used to solve mass transfer in complicated modules of a microfluidic device, such as mixing channels. Then, the mass transfer in a microfluidic device was solved in system-level. The macro-micro modeling method was applied to a micromixer, and the concentration distribution in the micromixer can be evaluated. Compared with numerical simulation, the maximum relative deviation between macro-micro calculation and numerical simulation, results are 1.28% and the computational efficiency of macro-micro model was improved significantly with the numbers of straight channels increasing. The macro-micro modeling method is proven to be an effective way for rapid design of microfluidic devices in system-level.
    Analytical methods 07/2012; 4(8):2334-2340. · 1.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Injection molding PMMA microfluidic chips can significantly improve the efficiency of chips forming. However, due to the coexistence of macro and micro effects in the injection molding process, the thickness uniformity of molding substrates is poor, which will seriously affect the thermal bonding quality of chips. In this paper, the effect of injection molding PMMA microfluidic chips thickness uniformity on the thermal bonding ratio and the quality of micro-channels was studied by experiments and simulations. The results show that when the following three conditions were satisfied during injection molding process, chips bonding ratio reaches to 93.9 % and the distortions of micro-channels caused by thermal bonding were acceptable. Firstly, the cover plates flatness error is smaller than 50–60 μm and substrates flatness error is smaller than 80–90 μm. Secondly, the maximum thickness difference of stack chips (cover plate stack with substrate) is smaller than 70–80 μm. Thirdly, chips thickness of the middle is larger than that of the two ends along their length direction and chips thickness distribute evenly along their width direction. These conclusions can be used for the parameters selection and moulds design during injection molding process of PMMA microfluidic chips.
    Microsystem Technologies 06/2012; 18(6). · 0.95 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A multilayer polydimethylsiloxane microdevice for cell-based high-throughput drug screening is described in this paper. This established microdevice was based on a modularization method and it integrated a drug/medium concentration gradient generator (CGG), pneumatic microvalves and a cell culture microchamber array. The CGG was able to generate five steps of linear concentrations with the same outlet flow rate. The medium/drug flowed through CGG and then into the pear-shaped cell culture microchambers vertically. This vertical perfusion mode was used to reduce the impact of the shear stress on the physiology of cells induced by the fluid flow in the microchambers. Pear-shaped microchambers with two arrays of miropillars at each outlet were adopted in this microdevice, which were beneficial to cell distribution. The chemotherapeutics Cisplatin (DDP)-induced Cisplatin-resistant cell line A549/DDP apoptotic experiments were performed well on this platform. The results showed that this novel microdevice could not only provide well-defined and stable conditions for cell culture, but was also useful for cell-based high-throughput drug screening with less reagents and time consumption.
    Journal of Micromechanics and Microengineering 06/2012; 22(6). · 1.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The so‐called “Bird's Nest” (the framework of the Beijing National Stadium as depicted on the cover), bears a resemblance to the rigid porous catalyst constructed for highly efficient heterogeneous asymmetric organocatalysis by W. Wang et al., reported in their Communication on page 6718 ff. The chiral porous polymer containing the Jørgensen–Hayashi catalyst shows excellent activity in the asymmetric Michael addition reaction.
    Chemistry 05/2012; 18(22). · 5.70 Impact Factor

Publication Stats

85 Citations
122.39 Total Impact Points


  • 2006–2014
    • Dalian University of Technology
      Lü-ta-shih, Liaoning, China
  • 2012
    • Lanzhou University
      • State Key Laboratory of Applied and Organic Chemistry
      Lanzhou, Gansu Sheng, China
  • 2008
    • Zhejiang University
      • Department of Chemistry
      Hangzhou, Zhejiang Sheng, China