Key Engineering Materials Vols. 562-565

Abstract: Paper-based microfluidic devices have a significant potential for low-cost diagnostics in the developing world. This study reported a simple fabrication method based on the digitallization of microfluidic technology for paper based microfluidic devices. Melted wax was jetted steadily with PZT actuated microfluidic pulse inertia driving system and pulled-forged glass micronozzle in the form of droplets. The wax melted into filter paper to form hydrophobic wall and different patterns for paper microfluidic devices were made. The influence of system parameters such as driving force, frequency, the fabrication process and the tip diameter of glass micronozzle on the wax line width was experimentally studied. 75 μm500 μm wax lines were achieved with the wax printing system. The paper microfluidic devices fabricated could lead the capillary action of black ink and the color change reaction of NaOH and phenolphthalein solution. Result showed that the wax printing system is simple structured and this method suggests a novel path to develop simple, inexpensive, and portable diagnostic assays.

Abstract: This paper dedicated to the investigations of anode mass transfer characteristics of single serpentine, double serpentine, triple serpentine and quadruple serpentine flow fields to choose the best flow field structure. In this paper, the structure sizes of anode different serpentine flow fields have been designed to make the same duty cycle based on the theory analysis. Then a multi-physics 3D model has been established and simulated to analyze and compare mass transfer characteristics of every serpentine flow fields including pressure distributions, velocity distributions and concentration distributions. The current collector plates containing different serpentine flow fields have been made by micromachining. To verify the simulation analysis, the μ-DMFCs with different serpentine flow fields have been packaged and tested. Compared with the simulations, the experiment results come up with the conclusion that the performance of μ-DMFC with double serpentine flow field is a bit higher than those with others. In conclusion, though the cell performance with double serpentine flow field is a bit higher than that with others, its fabrication process is so complicated and the improvement of the performance is not obvious. It is concluded that increasing the serpentine channels of anode flow field doesn’t have many benefits on the cell performance.

Abstract: Electrohydrodynamic Direct Writing (EDW) based on Near-Field Electrospinning (NFES) is a novel method to fabricate aligned micro/nano structure. In this article, linear motors and PIV&F servo control algorithm are introduced to set up an EDW experiment platform, by which patterned micro/nano structure can be direct-written. The motion track and position of collector is adjusted accurately by the platform, thus the deposition position and pattern of direct-written micro/nano structure can be controlled according to the pre-designed pattern. When motion velocity of collector higher than the ejection jet, micro/nano structure in straight line can be gained; but twisted structure can be direct-written under lower motion velocity of collector. The standstill of collector is introduced to overcome the pattern distortion that stems from the sharp change of collector motion track and the inertia of following jet. With the help of motion standstill, the patterned micro/nano structure without distortion can be direct-written, and more jet would be deposited at the corner of the pattern leaded to coiled structure. The EHD platform builds up the based for the industrial application of 1D micro/nano structure.

Abstract: The traditional methods used to prepare diet microcapsules have disadvantages of expensive, complicated operation and harsh preparation conditions and so on. In this paper, based on the Digitalization of Microfluids Technology, a new method for preparing and research diet microcapsules is proposed, in which a kind of electromagnet is used as the actuator. Two kinds of micronozzle, one is the single micronozzle, and the other one is micronozzle array, are used to prepare diet microcapsules, and the influence of the system parameters on the stability of microcapsule preparation is explored. Results show that the sizes of the diet microcapsules could be controlled by changing the inner diameter of the micronozzle, the diet microcapsules could be prepared efficiently and steadily by the frequency of 7-11Hz range cooperated with other system parameters. Compared with the traditional methods, this method has the advantages of low-cost, mild preparation conditions, good controllability, and no limit to material and so on. With these obvious advantages, the technology offers researchers a tool to prepare diet microcapsules contain a variety of nutrients.

Abstract: Silver nanoplates, also referred to as nanoprisms or nanodisks, are two-dimensional plasmonic nanostructures that have attracted intensive attention due to their strong shape-dependent optical properties and related applications. In order to obtain the silver nanoplates with high concentration, the liquid-phase reduction method was adopted. Silver nanoparticles colloid was obtained by reducing the high molar concentration of AgNO3 (up to 3.17 M) with the hydrazine hydrate (H4N2 • H2O) as reductant in the presence of polyethylene pyrrole (PVP) as the protectant. 0.5 M Sodium Citrate is introduced into the precursor aqueous which containing AgNO3 and PVP, the molar ratio of PVP to AgNO3 was tuned from 0.64 to 1.5. When molar is 1.5, the mainly particles are silver nanospheres, on the contrary, the nanospheres are transferred into nanoplates as the ratio decreased gradually, until the mainly product are nanoplates. The constituent of the silver nano-clusters was established by performing the Powder X-ray diffraction. The nano-silver dispersion with average diameter is about 113.2 nm were finally deserved. The size distribution of the silver nanoparticles is recorded by the Zeta potential analyzer. Scanning electron microscope (SEM) was used to characterize the morphology of the nano-silver particles. The silver content is about 3%. Nano-silver colloid is obtained and purified by centrifugation and wash with deionized water and ethanol. Then, water-based silver conductive ink is obtained by adding some amount deionized water and additives and adjusted parameters, which could be widely used in printed electronics.

Abstract: The microfluidic chip with well-defined structure is an important platform for cell research. The existing techniques for chip fabrication especially in cell biology and tissue engineering have many defects, for example, poor processing precision, high processing cost, as well as sophisticated manufacturing procedure. Thus, fabrication of simple and practicable microfluidic chip with highly efficient cell control ability and low-cost is turned to be the main target for bioengineering application. Poly(ethylene glycol) (PEG) is a hydrophilic polymer. Substituting terminal hydroxyl groups with acrylates, forming poly(ethylene glycol) diacrylate (PEGDA), allows the polymer to be cross-linked to form a three-dimensional polymer network. Meanwhile the use of photopolymerization can realize precise and temporal control of polymerization for formation of complex shapes. Herein, we utilize PEGDA hydrogel’s highly tunable characteristic, using photopolymerization method to obtain desirable micro-structure. Each chip has four of uniform micro-structures, which can carry multiple parallel experiments at the same time. We also add 2-Hydroxyethyl Methacrylate (HEMA) to the PEGDA prepolymer in order to increase the cell adhesion capacity of the microchip surface for cell culture. The experimental results showed that this method can achieve double-layer cell culture with short time treatment. Cells can be well captured and cultured in the hydrogel microfluidic chip with excellent activity. The hydrogel microfluidic chip has the potential of practicable application once large-scale preparation is accomplished.

Abstract: Electrostatic micro-devices are simple but important for MEMS applications. Precise dynamic descriptions of these devices are often hard to obtain due to the electrostatic nonlinearity and the fluid-structure interactions in devices. Here we present a comprehensive electrostatic-mechanical-fluidic coupling transient analysis for the pull-in process of two ends fixed micro-plate device. The numerical results are compared with the published experiment works of other researchers available in the literature, and thus the model had been validated. After that the proper orthogonal decomposition approach is performed for the snapshot matrixes which are sampled from an ensemble of the fully finite element results. The resulted spatial distribution modes of pressure show a higher spatial frequency toward the middle of the micro-plate, which indicates that the pressures at the moving edges of the plate are not equal to ambient pressure. Due to the increasing demands for simulation accuracy, the electrostatic-mechanical interactions and the nonlinear features of viscous loss from the surrounding fluid have to be taken into account in details.

Abstract: Design, fabrication and test results of a lateral DC-contact RF-MEMS switch for mm-wave applications are presented. The switch is driven by a triple cascaded electrothermal buckle-beam actuator, which can generate large displacements and contact forces at lower temperatures than traditional electrothermal actuators. The size of the whole switch is only 1.2 mm × 1.4 mm in area. The measured transient times for switch-on and switch-off are 13.6 and 0.96 ms, respectively. Low insertion losses and high isolation of 0.17 dB and 26.7 dB, respectively, are obtained in the proposed switch at center frequency of 35GHz, the insertion losses less than 0.5dB and the isolation better than 22.5dB can be achieved in the proposed switch at 30~40GHz. The reasonable agreement between design and measurement is observed.

Abstract: A novel micro-sensing chip for detecting total nitrogen (TN) was reported, which was based on 3D bimetallic Ag/Pd nanodendrites for electrocatalystic reduction of nitrate. The 3D structured Ag/Pd nanodendrites were synthesized by electrodepositon of Ag and Pd on gold interdigitated microband array electrode (Au-IDA). Such 3D Ag/Pd bimetallic nanodendrites possess an extremely high electrocatalytic activity for nitrate reduction in alkaline media at pH 12.5 hence realizing an excellent performance of TN determination without pH adjusting. The electrochemical detection limit of TN is 0.1mgL^-1 and the measurement results of real water samples showed a relative error of less than 10% with UV spectrophotometric method. The present micro-sensing chip has significant potential for developing of portable and inexpensive TN instrument for on-line environmental measurement.

Abstract: Nanopore and nanopore based bio-sensing technology have become into more and more interesting research area in the past ten years. In this work, micro-pore in Si-S₃N₄ chips was fabricated and characterized by Focused Ion Beam (dual Beam), and then the S₃N₄ pore was covered by Polycarbonate (PC) membrane containing 50nm nanopores and sealed by using polydimethylsiloxane (PDMS) to get hybrid micro-nanopores. The obtained chip with hybrid nanopores together with two liquid cells was integrated into an ionic current detection device for biosensing. Based on this device, λ-DNA in the electrolytic solution can be detected when it is electrophoretically driven through the hybrid nanopores, and different gestures of λ-DNA in translocation also can be discriminated.