Chong Liu

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

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Publications (56)84.48 Total impact

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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: 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: 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: 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: “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: 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: 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 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 01/2012; 22(6). · 1.79 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
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    ABSTRACT: In this paper, a 6 wt% carbon nano-suspension was prepared and atomized using electrohydrodynamic atomization technique. The different atomization modes at certain regions of working parameters (applied voltage and flow rate) were studied. In the stable cone-jet mode, the effect of the working distance (distance between needle exit and substrate) on the size and distribution of the deposited relics was examined. It was observed that higher working distance resulted in larger size and higher number density of relics, mainly at the range of 0.2–0.4 µm. A continuous carbon line with the width of ~50 µm was also print-patterned using the electrohydrodynamic atomization deposition technique from the carbon nano-suspension.
    Proceedings of the Institution of Mechanical Engineers Part N Journal of Nanoengineering and Nanosystems 12/2011; 225(4):149-154.
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    ABSTRACT: Stomatal transpiration, which is an efficient way to carry water from the roots up to the leaves, can be described by "diameter-law". According to the law, the flow rate induced by micropore transpiration far exceeded that induced by macroscale evaporation, and it can be controlled by opening (or closing) some micropores. In this research, a bio-inspired micropump based on stomatal transpiration is presented. The micropump is composed of three layers: the top layer is a 93 μm-thick PVC (polyvinylchloride) film with a group of slit-like micropores; the second layer is a PMMA sheet with adhesives to join the other two layers together; the third layer is a microporous membrane. Using this pump, controllable flow rates of 0.13-3.74 μl min(-1) can be obtained. This micropump features high and adjustable flow-rates, simple structure and low fabrication cost. It can be used as a "plug and play" fluid-driven unit without any external power sources and equipment.
    Lab on a Chip 07/2011; 11(16):2785-9. · 5.70 Impact Factor
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    ABSTRACT: During a SU-8 lithographic process, poor adhesion performance between the SU-8 photoresist and metal substrate usually contributes to the failure of the binding. More seriously, the lithography can even be completely compromised. This significantly restricts the improvement of image resolution and enhancement of depth-to-width ratio. Concerning this problem, an indentation method was adopted to test the adhesion strength between the SU-8 and stainless steel substrate in this study. By a dimensional analysis method, empirical formula accounting for indentation stress was deduced from Evans model. Interface fracture energy release rate was also obtained to characterise interface adhesion strength. Simulation was performed based on the commercial finite element package ANSYS, and its results were compared with corresponding indentation experiment results. The good agreement of these two results demonstrated the applicability of the modified empirical formula. Besides, the influence factors of adhesion performance were discussed. The result indicated that the existence of internal stress could prompt interfacial fracture, whereas increasing substrate roughness could improve interface adhesion strength.
    Micro & Nano Letters 07/2011; · 0.85 Impact Factor
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    ABSTRACT: A three-layer poly (methyl methacrylate) (PMMA) electrophoresis microchip integrated with Pt microelectrodes for contactless conductivity detection is presented. A 50 μm-thick PMMA film is used as the insulating layer and placed between the channel plate (containing the microchannel) and the electrode plate (containing the microelectrode). The three-layer structure facilitates the achievement of a thin insulating layer, obviates the difficulty of integrating microelectrodes on a thin film, and does not compromise the integration of microchips. To overcome the thermal and chemical incompatibilities of polymers and photolithographic techniques, a modified lift-off process was developed to integrate Pt microelectrodes onto the PMMA substrate. A novel two-step bonding method was created to assemble the complete PMMA microchip. A low limit of detection of 1.25 μg ml(-1) for Na(+) and high separation efficiency of 77,000 and 48,000 plates/m for Na(+) and K(+) were obtained when operating the detector at a low excitation frequency of 60 kHz.
    Lab on a Chip 03/2011; 11(5):969-73. · 5.70 Impact Factor
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    ABSTRACT: A passive micro direct methanol fuel cell (DMFC) for reducing volume and parasitic power is designed and fabricated using several integrated technologies. New bipolar plates with tapered channels at the anode and a pillar array at the cathode are first applied to a passive micro-DMFC. The substrate of the bipolar plates made of acrylonitrile butadiene styrene (ABS) is hot embossed with two molds, fabricated by UV-LIGA and micro machining. To make the bipolar plates conductive and hydrophilic, a nickel layer is electroplated on the ABS plates, and three PDDA/PSS bi-layers are self-assembled onto the nickel layer. The bipolar plates are produced using hot embossing, a low cost, highly accurate batch process. A single cell is assembled to verify the self-pumping function, and it can generate a peak power density of 7.4mWcm−2 with a 3M methanol solution. The fuel cell is verified to work in three different orientations. When the fuel cell is placed horizontally, the self-pumping rate is about 0.1–0.15mLh−1. And the fuel cell can work through self-pumping for 5h under this condition.
    Lancet. 01/2011; 196(18):7533-7540.
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    ABSTRACT: Compression pressure has significant influence on the performance of direct methanol fuel cell (DMFC) and the effect of compression is more significant for a DMFC than a proton exchange membrane fuel cell (PEMFC). But there are few data concerning the compression pressure on the performance of DMFCs. Loading history and feeding mode may also affect the optimal compression pressure for the DMFC. This paper investigates the influence of compression pressure on the DMFC. The effects of reload and air feeding mode are also examined. The optimal pressure of the DMFC is 1MPa when the cell is assembled for the first time in forced convection mode. However, the optimum pressure decreases to 0.05MPa when the cell is compressed again because of the residual strain of the GDL. The optimal pressure decreases to 0.5MPa when the cell operates in air-breathing mode. Therefore, the optimum compression pressure for a DMFC strongly depends on the loading history and the feeding mode.
    Journal of Power Sources 01/2011; 196(1):264-269. · 4.68 Impact Factor
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    ABSTRACT: In land plants, water vapor diffuses into the air through the stomata. The loss of water vapor creates a water potential difference between the leaf and the soil, which draws the water upward. Quantitatively, the water potential difference is 1–2 MPa which can support a water column of 100–200 m. Here we present the design and operation of a biomimetic micropump. The micropump is mainly composed of a 48-μm thick metal screen plate with a group of 102-μm diameter micropores and an agarose gel sheet with nanopores of 100 nm diameter. The micropores in the screen plate imitate the stomata to regulate the flow rate of the micropump. The agarose gel sheet is used to imitate the mesophyll cells around the stomata. The lost of water from the nanopores in the gel sheet can generate a water potential difference (more than 30 kPa) which can drive solution flow in a microfluidic chip. Results have shown that a precise flow rate of 4–8 nl/min can be obtained by using this micropump, and its ultra-high flow rate is 113–126 nl/min. The advantages of this biomimetic micropump include adjustable flow rate, simple structure and low fabrication cost. It can be used as a “plug and play” fluid-driven unit in microfluidic chips without any external power sources or equipments.
    Microfluidics and Nanofluidics 01/2011; · 3.22 Impact Factor