[Show abstract][Hide abstract] 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.
No preview · Article · Oct 2015 · Analytical methods
[Show abstract][Hide abstract] ABSTRACT: The effects of silica nanoparticles on the properties of a commonly used Sylgard 184 polydimethylsiloxane (PDMS) in microfluidics were systemically studied. Two kinds of silica nanoparticles, A380 fumed silica nanoparticles and MCM-41 mesoporous silica nanoparticles, were individually doped into PDMS, and the properties of PDMS with these two different silica nanoparticles were separately tested and compared. The thermal and mechanical stabilities of PDMS were significantly enhanced, and the swelling characteristics were also improved by doping these two kinds of nanoparticles. However, the transparency of PDMS was decreased due to the light scattering by nanoparticles. By contrast, PDMS/MCM-41 nanocomposites showed a lower coefficient of thermal expansion (CTE) owing to the mesoporous structure of MCM-41 nanoparticles, while PDMS/A380 nanocomposites showed a larger elastic modulus and better transparency due to the smaller size of A380 nanoparticles. In addition, A380 and MCM-41 nanoparticles had the similar effects on the swelling characteristics of PDMS. The swelling ratio of PDMS in toluene was decreased to 0.68 when the concentration of nanoparticles was 10 wt %.
[Show abstract][Hide abstract] ABSTRACT: Co-conversion of alkane with another reactant over zeolite catalysts has emerged as a new approach to the long-standing challenge of alkane transformation. With the aid of solid-state NMR spectroscopy and GC-MS analysis, it was found that the co-conversion of propane and methanol can be readily initiated by hydride transfer at temperatures of ≥449 K over the acidic zeolite H-ZSM-5. The formation of 13C-labeled methane and singly 13C-labeled n-butanes in selective labeling experiments provided the first evidence for the initial hydride transfer from propane to surface methoxy intermediates. The results not only provide new insight into carbocation chemistry of solid acids, but also shed light on the low-temperature transformation of alkanes for industrial applications.
No preview · Article · May 2015 · Angewandte Chemie
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · Key Engineering Materials
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · Key Engineering Materials
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · Key Engineering Materials
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
No preview · Article · Jan 2015 · Microsystem Technologies
[Show abstract][Hide abstract] ABSTRACT: Introduction:
Heavy cigarette smoking-related chronic obstructive pulmonary disease is an independent risk factor for lung squamous carcinoma. However, the mechanisms underlying the malignant transformation of bronchial epithelial cells are unclear.
In our study, human tumor-adjacent bronchial epithelial cells were obtained from 10 cases with smoking-related chronic obstructive pulmonary disease and lung squamous carcinoma and cultured in an established microfluidic chip for continual exposure to cigarette smoke extracts (CSE) to investigate the potential tumor-like transformation and mechanisms. The integrated microfluidic chip included upstream concentration gradient generator and downstream cell culture chambers supplied by flowing medium containing different concentrations of CSE.
Our results showed that continual exposure to low doses of CSE promoted cell proliferation whereas to high doses of CSE triggered cell apoptosis. Continual exposure to CSE promoted reactive oxygen species production in human epithelial cells in a dose-dependent manner. More importantly, continual exposure to low dose of CSE promoted the epithelial-to-mesenchymal transition process and anchorage-independent growth, and increased chromosome instability in bronchial epithelial cells, accompanied by activating the GRP78, NF-κB, and PI3K pathways.
The established microfluidic chip is suitable for primary culture of human tumor-adjacent bronchial epithelial cells to investigate the malignant transformation. Continual exposure to low doses of CSE promoted tumor-like transformation of human nontumor bronchial epithelial cells by inducing reactive oxygen species production and activating the relevant signaling.
No preview · Article · Aug 2014 · Journal of thoracic oncology: official publication of the International Association for the Study of Lung Cancer
[Show abstract][Hide abstract] 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)
No preview · Article · Jul 2014 · Journal of Micro/ Nanolithography, MEMS, and MOEMS
[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.
No preview · Article · May 2014 · Biomedical Microdevices
[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.
No preview · Article · Mar 2014 · Journal of Experimental Nanoscience
[Show abstract][Hide abstract] 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.
[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.
No preview · Article · Feb 2014 · Journal of Micromechanics and Microengineering
[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.
No preview · Article · Feb 2014 · Chinese Journal of Analytical Chemistry
[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.
No preview · Article · Jan 2014 · Micro & Nano Letters