Chong Liu

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

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Publications (58)89.07 Total impact

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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; · 2.72 Impact Factor
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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. · 1.79 Impact Factor
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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; · 0.83 Impact Factor
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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. · 0.85 Impact Factor
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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 01/2014; 9(3). · 0.88 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. 01/2014; 42(2):166–172.
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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; · 0.83 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). · 3.79 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 01/2013; · 0.83 Impact Factor
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    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.
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    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. · 1.22 Impact Factor
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    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
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    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
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    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. · 1.86 Impact Factor
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    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). · 0.83 Impact Factor
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    ABSTRACT: A new method of water pretreatment for thermal bonding polymethylmethacrylate microfluidic chip was proposed in this paper. The bonding rate (effective bonding area) of microfluidic chip under different pretreatment time was studied and the mechanism of this method was discussed. The main thermal bonding parameters were as follows: bonding pressure 1.4 ~ 1.9 Mpa, temperature 91 ~ 93°C, time 360 s. The experimental result shows that this method can increase the effective bonding area, improve the bonding quality of the microfluidic chip compared to the conventional thermal bonding method. The optimal water pretreatment time is 1 h with the bonding rate increased by 34% compared with the conventional thermal bonding method. The pollution to the micro-channels is avoided and the performance of the microfluidic system will be reserved with this water pretreatment method. This method is available for the biochemical analysis of the chip, and holds the benefits of easy-operation, high-efficiency and low-cost properties.
    Microsystem Technologies 04/2012; 18(4). · 0.83 Impact Factor
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    ABSTRACT: Face verification has broad potential in varieties of multimedia applications, such as security access control, surveillance monitor, image retrieval and intelligent human machine interface. However, the existence of variable lighting, pose, facial expression, aging and other random factors often causes the occurrence of recognition errors. Further upgrading the performance of face verification systems is not only a challenging but also an urgent task. Information fusion had proved to be one of the promising approaches in upgrading verification performance since more cues and evidences were provided. Gabor feature face representation and Curvelet feature face representation were chosen for fusion processing, since both representations are good at depicting image intrinsic pattern but with different emphases. After calculating the Gabor features and Curvelet features of a face image, the mutually correlated projection pairs of these two individual mode features were first yielded by canonical correlation analysis (CCA) method. Then, an integrate projection set can be built by simply grouping these two mutual correlated projection sequences term by term correspondingly. The integrate projection set possesses most of the information contained in Gabor features and Curvelet features and is optimally reorganized in a correlation sense. To further enhance the discriminant capabilities, a linear discriminant analysis (LDA) post-processing is applied on the integrate projection set to yield the final fusion feature set. The experiment results testing on MBGC data set show that the proposed fusion approach does reduce the error rates significantly as compared with using individual mode feature alone. FRR100 and FAR1000 were reduced about 30% and more. KeywordsFeature fusion–Face verification–Curvelets–Gabor wavelets
    Multimedia Tools and Applications 04/2012; 57(3):549-563. · 1.01 Impact Factor
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    ABSTRACT: We presented a deposited microbead plug (DMBP)-based microfluidic device capable of extracting plasma from whole blood by capillary forces. This device was fabricated by reversibly bonding a PDMS slab with a straight channel to a hydrophilic glass substrate. The DMBP was easily constructed at the inlet of the channel within 2 min by a method of natural deposition of microbeads without the need of weirs or photopolymerization. Capillary forces generated mainly on the hydrophilic glass substrate provided a driving force during the fabrication of the DMBP and plasma extraction, resulting in simplicity of operations. The DMBP only allows blood plasma to pass through but blocks blood cells, which was demonstrated experimentally using sheep blood. The DMBP enabled to remain in its initial configuration during plasma extraction. The high quality plasma was obtained without contamination of microbeads and blood cells. This easy-to-use, easy-to-integrate, disposable the DMBP-based microfluidic device has the potential to be integrated with on-chip bioanalytical units for the applications of point-of-care diagnostics.
    Biomedical Microdevices 03/2012; 14(3):565-72. · 2.72 Impact Factor
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    ABSTRACT: In this Letter, electrohydrodynamic atomisation (EHDA) was used to spray deposit Pt/C catalyst films using a Pt/C nanosuspension. In stable cone-jet atomisation mode, the influence of flow rate on the characteristics of relics and films was analysed. At a lower flow rate smaller size and lower number density of relics were predominant, which led to the formation of porous films; conversely, higher flow rate generated dense films. The size of the relics in experimental results and theoretically predicted size were compared and analysed. The dispersive X-ray analysis confirms that the EHDA deposited films are Pt/C.
    Micro & Nano Letters 01/2012; 7(3):235-239. · 0.85 Impact Factor
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    ABSTRACT: A simple O2 plasma etching method is developed and first used to fabricate planar nanofluidic channels in thermoplastic polymers. In this process, a copper etching mask with a micron-scale width is made by traditional UV lithography and wet etching on a polymer substrate, then the polymer substrate is etched by O2 plasma in a commonly used plasma cleaner to form the planar nanochannel. Effects of the process parameters of the plasma cleaner on the etching rate are studied. The average etching rate for most thermoplastic polymers used in lab-on-a-chip is about 10 nm/min and the surface roughness is less than 2 nm when radio frequency power and chamber pressure are 60 W and 200 Pa, respectively. To demonstrate this method, a polymethylmethacrylate (PMMA) micro-nanofluidic chip containing nine parallel nanochannels, 100 nm in depth, 5 μm wide and 1 mm long, is fabricated to investigate the ion enrichment of 1 M fluorescein isothiocyanate (FITC) in 10 mM phosphate buffered saline (PBS) buffer.
    Micro & Nano Letters 01/2012; 7(2):159-162. · 0.85 Impact Factor