Hot embossing and thermal bonding of poly(methyl methacrylate) microfluidic chips using positive temperature coefficient ceramic heater

As a self-regulating heating device, positive temperature coefficient ceramic heater was employed for hot embossing and thermal bonding of poly(methyl methacrylate) microfluidic chip because it supplied constant-temperature heating without electrical control circuits. To emboss a channel plate, a piece of poly(methyl methacrylate) plate was sandwiched between a template and a microscopic glass slide on a positive temperature coefficient ceramic heater. All the assembled components were pressed between two elastic press heads of a spring-driven press while a voltage was applied to the heater for 10 min. Subsequently, the embossed poly(methyl methacrylate) plate bearing negative relief of channel networks was bonded with a piece of poly(methyl methacrylate) cover sheet to obtain a complete microchip using a positive temperature coefficient ceramic heater and a spring-driven press. High quality microfluidic chips fabricated by using the novel embossing/bonding device were successfully applied in the electrophoretic separation of three cations. Positive temperature coefficient ceramic heater indicates great promise for the low-cost production of poly(methyl methacrylate) microchips and should find wide applications in the fabrication of other thermoplastic polymer microfluidic devices.     

Low-temperature direct bonding of glass nanofluidic chips using a two-step plasma surface activation process

Owing to the well-established nanochannel fabrication technology in 2D nanoscales with high resolution, reproducibility, and flexibility, glass is the leading, ideal, and unsubstitutable material for the fabrication of nanofluidic chips. However, high temperature (~1,000 °C) and a vacuum condition are usually required in the conventional fusion bonding process, unfortunately impeding the nanofluidic applications and even the development of the whole field of nanofluidics. We present a direct bonding of fused silica glass nanofluidic chips at low temperature, around 200 °C in ambient air, through a two-step plasma surface activation process which consists of an O₂ reactive ion etching plasma treatment followed by a nitrogen microwave radical activation. The low-temperature bonded glass nanofluidic chips not only had high bonding strength but also could work continuously without leakage during liquid introduction driven by air pressure even at 450 kPa, a very high pressure which can meet the requirements of most nanofluidic operations. Owing to the mild conditions required in the bonding process, the method has the potential to allow the integration of a range of functional elements into nanofluidic chips during manufacture, which is nearly impossible in the conventional high-temperature fusion bonding process. Therefore, we believe that the developed low-temperature bonding would be very useful and contribute to the field of nanofluidics.     

Glass microfabricated nebulizer chip for mass spectrometry

A microfluidic nebulizer chip for mass spectrometry is presented. It is an all-glass device which consists of fusion bonded Pyrex wafers with embedded flow channels and a nozzle at the chip edge. A platinum heater is located on the wafer backside. Fabrication of the chip is detailed, especially glass deep etching, wafer bonding, and metal patterning. Various process combinations of bonding and metallization have been considered (anodic bonding vs. fusion bonding; heater inside/outside channel; metallization before/after bonding; platinum lift-off vs. etching). The chip vaporizes the liquid sample (0.1-10 microL min(-1)) and mixes it with a nebulizer gas (ca. 100 sccm N2). Operating temperatures can go up to 500 degrees C ensuring efficient vaporization. Thermal insulation of the glass ensures low temperatures at the far end of the chip, enabling easy interconnections.     

聚甲基丙烯酸甲酯微流控分析芯片的简易热压制作法

提出聚甲基丙烯酸甲酯(PMMA)微流控分析芯片的一种简易热压制作法,研究了镍基、单晶硅和玻璃3种阳模制备芯片及芯片的封合条件.采用扫描电镜(SEM)和电荷耦合检测器(CCD)对PMMA芯片的微通道及其横截面形貌进行了表征.SEM图和CCD图表明实现了热压封接.测定了PMMA芯片的伏安曲线和电渗流,其电渗流值与文献报道值基本一致.本法制作的PMMA芯片用于电泳分离Cy5荧光染料,峰高RSD为2.2%(n=11),理论塔板数7.4×10⁴m^-1.     

Low temperature bonding of poly(methylmethacrylate) electrophoresis microchips by in situ polymerisation

A novel method for bonding poly(methyl methacrylate) (PMMA) electrophoresis microchips at the temperature below the glass transition temperature of PMMA based on in situ polymerization has been demonstrated. Methyl methacrylate (MMA) containing initiators was allowed to prepolymerize in an 85 degrees C water bath for 8 min and 15 min to produce a bonding solution and a dense molding solution, respectively. The channel plate of the PMMA microchip was fabricated by the UV-initiated polymerization of the molding solution between a nickel template and a PMMA plate at room temperature. Prior to bonding, the blank cover was coated with a thin layer of the bonding solution and was bonded to the channel plate at 95 degrees C for 20 min under the pressure of binder clips. The attractive performance of the PMMA chips bonded by the new approach has been demonstrated by separating and detecting dopamine, catechol, three cations, and three organic acids in connection with end-column amperometric detection and contactless conductivity detection.     

Fracture mechanism of metal electrode integrated on a chip and fabrication of a poly(ethylene terephthalate) electrophoresis microchip

Thermal bonding is an important technique to fabricate polymer electrophoresis microchip. However, the metal electrodes deposited on polymer substrate can readily fracture during the thermal bonding. In this paper, poly(ethylene terephthalate) (PET) was exploited to fabricate the electrophoresis microchip with an integrated gold electrode for amperometric detection. The fracture of the gold electrode was studied through FEA (finite element analysis) simulations, the potentially risk positions on the electrode were shown. The calculation results were tested by bonding experiments and were proven to be consistent with the experiments. Besides, an optimal bonding temperature for PET chip was also presented based on FEA simulations and bonding experiments. Considering the low surface properties of PET, oxygen plasma-assisted thermal bonding technique was used to enhance bonding. Upon treated for 150 s, the PET substrates could be thermally bonded at 62 °C without electrode fracture. The fabricated PET chips were demonstrated for detection of standard glucose solution. Satisfactory reproducibility was achieved, and the RSD values of peak height and migration time of the PET CE chips were 0.51% and 2.17%, respectively.     

Modification of amorphous poly(ethylene terephthalate) surface by UV light and plasma for fabrication of an electrophoresis chip with an integrated gold microelectrode

Amorphous poly(ethylene terephthalate) (PET), which possess a low softening temperature (T(s)=75 degrees C), was exploited to fabricate the electrophoresis chip with an integrated gold electrode for amperometric detection, with emphases being focused on the PET surface modification via UV light and air plasma. Both UV irradiation and plasma treatment were found to be able to improve the surface wettability, enhance the supported electroosmotic flow (EOF), and increase thermal bonding strength of PET sheets, with the latter being more efficient and less time-consuming than the former in the surface modification. Upon treated with plasma for 2 min, the PET sheets could be thermally bonded at 65 degrees C. T-peer test showed that the bonding strength increased from 10 g/cm for native PET sheets to 1250 g/cm for the plasma treated sheets when chips were bonded at the softening point, Attenuated-total-internal-reflection spectrum showed that, after being exposed to the UV light, carboxylic groups site-selectively formed in the UV-exposed region on PET surface. These UV-induced carboxylic groups were further utilized as the scaffold for preparation of micro-gold electrode via electroless gold plating. By using this established UV-directed electroless plating and the plasma-assisted thermal bonding techniques, the full PET electrophoresis chip with an integrated micro-gold electrode could be fabricated in common chemistry laboratory without the need of clean rooms. The fabricated PET chips were demonstrated for separation and detection of model analytes of dopamine (DA) and catechol (CA). Satisfactory resolution of the two analytes was achieved within 40s, and detection limits of 0.87 microM and 1.28 microM for DA and CA were obtained, respectively.     

Microchemical inhomogeneity to characterize atomic configurations in the heating and quenching of a CuHf2 alloy

Based on the constructed Cu-Hf interatomic potential, Monte Carlo simulations were conducted to reveal the atomic configurations in heating and quenching of a CuHf(2) alloy through scrutinizing the evolution of microchemical inhomogeneity. Simulations show that the CuHf(2) crystalline structure becomes more homogeneous during heating but an obvious drop in microchemical inhomogeneity appears when reaching its melting point. During the quenching process, the CuHf(2) melt becomes increasingly inhomogeneous and shows a change in the slope in the microchemical inhomogeneity around glass transition temperature. Simulation results were evidenced by the atomic packing analysis through the Voronoi tessellation method. The implications of our study suggest that the glass transition could be visualized as a process involving increase of microchemical inhomogeneity from the liquid to glassy state.     

tert-butylcarbene from 1,1-diiodoneopentane

When 1,1-diiodoneopentane is passed through a hot tube containing methyllithium-coated Pyrex chips, 1,1-dimethylcyclopropane and 2-methyl-2-butene are produced in near quantitative yield. The ratio of products indicates that the intermediate carbene is the same as is produced from thermal or photosensitized decomposition of tert-butyldiazomethane but different from that formed by direct irradiation of the diazo compound.     

Mechanical and chemical analysis of plasma and ultraviolet-ozone surface treatments for thermal bonding of polymeric microfluidic devices

Here we have demonstrated that radio frequency plasma and ultraviolet-ozone (UVO) surface modifications are effective treatments for enabling the thermal bonding of polymeric microfluidic chips at temperatures below the T(g) (glass transition temperature) of the polymer. The effects of UVO and plasma treatments on the surface properties of a cyclic polyolefin and polystyrene were examined with X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM) surface roughness measurements and surface adhesion measurements with AFM force-distance data. Three-point bending tests using a dynamic mechanical analyzer (DMA) were used to characterize the bond strength of thermally sealed polymer parts and the cross-sections of the bonded microchannels were evaluated with scanning electron microscopy (SEM). The experimental results demonstrated that plasma and UVO surface treatments cause changes in the chemical and physical characteristics of the polymer surfaces, resulting in a decrease in T(g) at the surface, and thus allowing the microfluidic chips to be effectively bonded at temperatures lower than the T(g) of the bulk polymer without losing the intended channel geometry.     

Microfluidic chip fabrication using hot embossing and thermal bonding of COP

The application of silicon mold inserts by micro‐hot embossing molding has been explored in microfluidic chip fabrication. For the mold insert, this study employed an SU‐8 photoresist to coat the silicon wafer. Ultraviolet light was then used to expose the pattern on the SU‐8 photoresist surface. This study replicates the microstructure of the silicon mold insert by micro‐hot embossing molding. Different processing parameters (embossing temperature, embossing pressure, embossing time, and de‐molding temperature) for the cycle‐olefin polymer (COP) film of microfluidic chips are evaluated. The results showed that the most important parameter for replication of molded microfluidic chip is embossing temperature. De‐molding temperature is the most important parameter for surface roughness of the molded microfluidic chip. The microchannel is bonded with a cover by thermal bonding processing to form the sealed microfluidic chip. The bonding temperature is the most important factor in the bonding strength of the sealed microfluidic chip. Copyright © 2009 John Wiley & Sons, Ltd.     

Practical integration of polymerase chain reaction amplification and electrophoretic analysis in microfluidic devices for genetic analysis

An integrated system of a silicon-based microfabricated polymerase chain reaction (microPCR) chamber and microfabricated electrophoretic glass chips have been developed. The PCR chamber was made of silicon and had aluminum heaters and temperature sensors integrated on the glass anodically bonded cover. Temperature uniformity in the reaction chamber was +/-0.3 degrees C using an improved novel "joint-heating" scheme. Thermal cycling was digitally controlled with a temperature accuracy of +/- 0.2 degrees C. Small operating volumes together with high thermal conductivity of silicon made the device well suited to rapid cycling; 16 s/cycle were demonstrated. For analysis of the PCR products, the chamber output was transferred to the glass microchip by pressure. Analysis time of PCR amplified genomic DNA was obtained in the microchip in less than 180 s. The analysis procedure employed was reproducible, simple and practical by using viscous sieving solutions of hydroxypropylmethylcellulose and dynamically coated microchip channels with poly(vinylpyrrolidone). DNA fragments that differ in size by 18 base pairs (bp) were resolved. Analysis of genomic male and female amplified DNA by microPCR was achieved in microchip, and application of the integrated microPCR-microchip for the identification of bird sex was tested. Genomic DNA samples from several bird species such as pigeon and chicken were analyzed. Hence, the system could be used as well to determine the sex of avian species.     

一种可逆键合电泳微芯片的制作及在蛋白质分离中的应用

阐述了一种可逆键合电泳微芯片的制作方法, 以及电泳微芯片在蛋白质分离、临床尿蛋白检测方面的应用. 用标准光刻腐蚀技术在石英基片上腐蚀泳道, 清洗腐蚀好的基片和盖片后, 在真空条件下实现键合. 此种方法键合制作的电泳微芯片可重复键合使用, 制得的电泳微芯片成功地用于标准蛋白质分离以及临床尿蛋白分析.     

Ceramic–glass composite high temperature seals for dense ionic-conducting ceramic membranes

A basic principle for selecting inorganic sealing materials for dense ionic-conducting ceramic membranes is described for high temperature permeation/reaction experiments. Based on this principle ceramic–glass composite seals consisting of the Pyrex glass and the ceramic powder of the membrane were developed and successfully used to seal a number of different dense ceramic membranes at high temperatures. The ceramic–glass composite seal is typically composed of 40–50 wt.% membrane material powder, 20–50 wt.% Pyrex glass and 5–20 wt.% additive such as sodium aluminate and boron oxide. The properties of ceramic–glass composite seal can be tailored to obtain suitable wettability, viscosity, chemical inertness, thermal expansibility, and bonding strength for good sealing results. A success rate for sealing these ceramic membranes of nearly 100% is possible using the ceramic–glass composite recipe if the correct sealing procedure, including seal paste preparation, is carefully followed.     

Solid‐state bonding of silicone elastomer to glass by vacuum oxygen plasma,atmospheric plasma,and vacuum ultraviolet light treatment

We experimentally demonstrated that treating a silicone elastomer by a vacuum oxygen plasma, an atmospheric pressure plasma, and vacuum ultraviolet (VUV) radiation resulted in different surface modifications that gave different contact angles, contact angle aging, and bond strengths. The aim of this study was to assess whether high‐throughput surface modification techniques of atmospheric pressure plasma and VUV radiation have the potential to replace conventional oxygen plasma modification. Four silicone elastomers with different hardnesses were used as specimens. The surfaces of all four silicone elastomers were successfully modified from hydrophobic to hydrophilic and they were also bonded to glass surfaces by the three surface modification techniques, although considerable variations were observed in the surface hydrophobicity and the bonding properties. The results clearly reveal that atmospheric pressure plasma and VUV treatment have the potential to replace conventional oxygen plasma treatment. In particular, VUV irradiation produced the most hydrophilic surface that was preserved for a long time. Thus, VUV irradiation is the most promising technique for realizing high‐throughput surface modification and bonding of silicone elastomers. Copyright © 2012 John Wiley & Sons, Ltd.     

Plasticizer-assisted bonding of poly(methyl methacrylate) microfluidic chips at low temperature

As an important phthalate plasticizer, dibutyl phthalate (DBP) was employed to decrease the bonding temperature of poly(methyl methacrylate) (PMMA) microfluidic chips in this work based on the fact that it can lower the glass transition temperature of PMMA. The channel plates of the PMMA microchips were fabricated by the UV-initiated polymerization of prepolymerized methyl methacrylate between a silicon template and a PMMA plate. Prior to bonding, DBP solution in isopropanol was coated on PMMA covers. When isopropanol in the coating was allowed to evaporate in air, DBP was left on the PMMA covers. Subsequently, the DBP-coated covers were bonded to the PMMA channel plates at 90 °C for 10 min under pressure. The channels in the complete microchips had been examined by optical microscope and scanning electron microscope. The results indicated that high quality bonding was achieved below the glass transition temperature of PMMA (∼105 °C). The performance of the PMMA microfluidic chips sealed by plasticizer-assisted bonding has been demonstrated by separating and detecting ionic species by capillary electrophoresis in connection with contactless conductivity detection.     

Depth-profiles within glass samples from anodic bonding experiments with copper using SNMS

Summary The bonding of copper plates to Pyrex 7740 glass has been studied for the encapsulation of microstructures fabricated with the LIGA technique. Although sufficient to join silicon to glass with 1 kV bonding voltage and 300°C, successful bonds of copper to glass could not be obtained. Depth-profiles using plasma-based SNMS with 410 eV argon ions were measured to check for migration processes within the glass component. To prevent charging of the insulating samples a 100 mpi woven Ta grid was used. Detection factors for the relevant elements were found to be unaffected by the grid. A matrix dependence of ca. ±30% was found. The depth resolution was 30 nm using the grid. The analysis of the glass after bonding attempts showed that massive migration of copper into the glass is probably preventing the necessary electrostatic attraction of the components at high temperatures. The temperature dependence of the copper migration was shown to increase steeply above 200°C. Insufficient sodium ion mobility prevents stable bonding at lower temperatures.     

Synthesis and optical properties of V2O5 nanorods

A two-step method was proposed in synthesizing V2O5 nanorods on planar substrates, i.e., depositing a V2O3 thin film at approximately 220 degrees C (by heating a pure sheet of vanadium in a rough vacuum) and then heating it in air at approximately 400 degrees C. The V2O5 nanorods produced by this technique are single crystalline and could emit intense visible light at room temperature, possibly due to some defects such as oxygen vacancies which got involved during growth. This study provides a simple and low-substrate-temperature route in fabricating V2O5 nanorods on planar substrates, which might be also applicable to other metal oxides.     

Miscible blends through hydrogen bonding: effects on polymer properties

Miscible blends through hydrogen bonding have been intensively studied. The effects of a variety of miscible hydrogen bonded polymer blends on properties such as thermal and thermal oxidative stability, moisture sensitivity, modulus and glass transition temperature are discussed. In addition, the preparation of semi-interpenetrating polymer networks (IPNs) and studies of the effect of crosslinking on the miscibility in hydrogen bonded polymer blends are reviewed.     

Hydrogen bonding configuration and thermal stability of ambient exposed and in situ hydrogenated polycrystalline diamond surfaces studied by high resolution electron energy loss spectroscopy

In this work we report on an investigation of hydrogen bonding and thermal stability on the surface of poly-crystalline diamond by high resolution electron energy loss spectroscopy (HR-EELS). Diamond films were grown on silicon substrates from CH(4)/H(2) as well as from CD(4)/D(2) gas mixtures by hot filament chemical vapor deposition (HF-CVD). The impact of ex situ ambient exposure on hydrogen bonding and its thermal stability was examined for: (i) as deposited films from a CH(4)/H(2) gas mixture; (ii) the same sample treated ex situ in micro-wave activated hydrogen plasma; and (iii) as deposited films from a CD(4)/D(2) gas mixture. In order to clarify the changes in the hydrogen bonding configuration detected on the different surfaces as a function of thermal annealing in situ hydrogenation by thermally activated atomic hydrogen was performed and examined. This study provides direct evidence that the exposure to ambient conditions and low temperature vacuum annealing have a pronounced effect on the hydrogen-carbon bonding configuration onto the poly-crystalline diamond surfaces.