Using an electro-spraying microfluidic chip to produce uniform emulsions under a direct-current electric field

An electro-spraying microfluidic chip was integrated with a parallel electrode and flow-focusing device to successfully generate uniform emulsions with an electric field. This approach utilizes a high electric field driven by a direct-current voltage to form a stable Taylor cone in the flow-focusing position. The Taylor cone can then generate stable and uniform emulsions that are less than 5?μm in diameter. The emulsion size is controlled by the surfactant concentration, the ratio of the water and oil phase flow rates and the strength of the electric field. When the strength of the electric field increases at a high surfactant concentration and low ratio of flow rates, the Taylor angle decreases, which causes the emulsion size to decrease. In this study, the water emulsion diameter ranged from 1 to 98?μm, and the poly(lactic-co-glycolic acid) (PLGA) emulsion size ranged from 7 to 70?μm. The microfluidic chip developed in this work has the advantages of actively controlling the emulsion size and generating uniform emulsions (the relative standard deviation was less than 10%) and represents a new emulsion generation process.     

微流控芯片及其应用

单层BD碟片容量为25GB、双层为50GB,基本上可以满足完全高清节目的记录播放。但是随着3D技术和互动技术的介入以及超大容量数据存储需求的增长,目前的BD标准将面临挑战。本文以工程实践的角度介绍了3种BD碟片的物理结构,并以此为基础,结合当前光存储领域的最新技术,从存储密度和数据传输率两方面展望了BD技术的发展趋势。     

聚二甲基硅氧烷微流体芯片的制作技术

基于MEMS技术的微流体芯片在分析化学和生物医学领域显示了巨大的应用潜力。作为构建微流体芯片的基底材料———聚二甲基硅氧烷(PDMS)已经表现出了许多的优点:良好的电绝缘性、较高的热稳定性、优良的光学特性以及简单的加工工艺等。采用浇注法制作了PDMS电泳微芯片,对PDMS微流体芯片的加工工艺、封装方法和结构特征进行了探讨,并提出了相应的解决方案。     

复合式微流控脱水芯片的研制

报道了一种复合式微流控脱水芯片。采用玻璃、聚二甲氧基硅氧烷(PDMS)和聚碳酸酯(PC)三种材质,采用不可逆封接方法分别制得玻璃—PDMS液路半芯片、PC—PDMS气路半芯片,中间夹一层聚四氟乙烯(PTFE)多孔滤膜,将两个半芯片可逆封接形成玻璃—PDMS…PDMS—PC结构的全芯片。该制备方法简单可靠,其液路半芯片和气路半芯片可以单独更换,使得使用成本降低。实验表明:该芯片脱水性能良好,可用于有机合成步骤中含水试剂的高效除水。     

Fabrication and in situ characterization of microcapsules in a microfluidic system

We have designed a microfluidic system that enables both the fabrication of calibrated capsules and the in situ characterization of their mechanical properties. The fabrication setup consists of a double flow-focusing system. A human serum albumin aqueous solution is introduced in the central channel of a first Y-junction. Intercepted by the lateral flows of a hydrophobic phase, it is dispersed into microdroplets. A cross-linking agent is then introduced at a second Y-junction allowing a membrane to form around the droplets. The time of cross-linking is controlled by the length of a wavy channel located downstream of the second junction. A cylindrical microchannel finally enables to deform and characterize the capsules thus formed. The mechanical properties of the capsule membrane are obtained by inverse analysis. The results show that the drop size increases with the flow rate ratio between the central and lateral channels. The mean shear modulus of the capsules fabricated after 23 s of cross-linking is of the order of the surface tension between the two phases indicating that a reaction time of 23 s is too short for an elastic membrane to form around the droplet. When the cross-linking time is increased to 60 s, the microcapsules surface is wrinkled, thus confirming that a solid membrane is formed around the drop. The mean shear modulus of the capsule membrane increases with the cross-linking time, which is in agreement with our previous chemical results and proves that a fine control of the mechanical properties is possible by choosing adequately the control parameters of the system.     

Chitosan microfiber fabrication using a microfluidic chip and its application to cell cultures

In this study, a poly-methyl-methacrylate (PMMA) microfluidic chip with a 45° cross-junction microchannel is fabricated using a CO₂ laser machine to generate chitosan microfibers. Chitosan solution and sodium tripolyphosphate (STPP) solution were injected into the cross-junction microchannel of the microfluidic chip. The laminar flow of the chitosan solution was generated by hydrodynamic focusing. The diameter of laminar flow, which ranged from 30 to 50 μm, was controlled by changing the ratio between chitosan solution and STPP solution flow rates in the PMMA microfluidic chip. The laminar flow of the chitosan solution was converted into chitosan microfibers with STPP solution via the cross-linking reaction; the diameter of chitosan microfibers was in the range of 50–200 μm. The chitosan microfibers were then coated with collagen for cell cultivation. The results show that the chitosan microfibers provide good growth conditions for cells. They could be used as a scaffold for cell cultures in tissue engineering applications. This novel method has advantages of ease of fabrication, simple and low-cost process.     

微流控芯片的材料与加工方法研究进展

综述了微流控芯片的制作材料及其加工方法的研究进展.在介绍了传统硅质材料,如硅、玻璃、石英等的基础上,着重描述了高分子聚合物材料在微流控芯片的应用趋势.针对不同材料,详叙了其材料特性、应用范围及加工方法.特别介绍了一些新的加工方法,如激光刻蚀法、软光刻、LIGA方法在该领域的应用.针对微流控芯片的材料与加工做了一个简要而...     

Using a cross-flow microfluidic chip for monodisperse UV-photopolymerized microparticles

In this paper, we report a microfluidic chip containing a cross-junction channel for the manipulation of UV-photopolymerized microparticles. Hydrodynamic-focusing is used to form a series of using 365 nm UV light to solidify the hydrogel droplets. We were able to control the size of the hydrogel droplets from 75 to 300 μm in diameter by altering the sample and by changing the flow rate ratio of the mineral oil in the center inlet channel to that of the side inlet channels. We found that the size of the emulsions increases with an increase in average velocity of the dispersed phase flow (polymer solution flow). The size of the emulsions decreases with an average velocity increase of the continuous phase flow (mineral oil flow). Experimental data show that the emulsions are very uniform. The developed microfluidic chip has the advantages of ease of fabrication, low cost, and high throughput. The emulsions generated are very uniform and have good regularity.     

Formation of fully closed microcapsules as microsensors by microfluidic double emulsion

Microcapsules templated from microfluidic double emulsions attract a great attention due to their broad new potential applications. We present a method to form transparent polymer microcapsules in small sizes of ~30 μm with aqueous cores and fully closed shells. We controlled the size ratio of the aqueous core to the polymer shell not only by flow rates of the double emulsions, but also by synergetic interaction between surfactants at the interface of immiscible fluids. We also found that fully closed shells can be formed by generating the double emulsion droplets in a jetting regime, in which the aqueous cores are confined centrally in the double emulsion droplets. We demonstrated the formation of barcodes in these microcapsules for multiplexed bioassays. These transparent microcapsules also have wide and high potentials for the development of various microsensors by functionalizing the liquid-state cores with compounds sensitive and responsive to temperature, light or electromagnetic field.     

高聚物微流控芯片上集成化气动微阀的研制

报道了一种新型的聚甲基丙烯酸甲酯(PMMA)/聚二甲基硅氧烷(PDMS)复合芯片。该芯片采用PMMA-PDMS…PDMS-PMMA的四层构型,以在芯片上集成气动微阀。具有液路和控制通道网路的PMMA基片与PDMS弹性膜间采用不可逆封接,分别形成液路半芯片和控制半芯片,而2个半芯片则依靠PDMS膜间的粘性实现可逆封接,组成带有微阀的全芯片。这种制备方法解决了制备PMMA-PDMS-PMMA三层结构芯片的封接难题,封接过程简单可靠。其控制部分和液路部分可以单独更换,可进一步降低使用成本,尤其适合一次性应用场合。初步实验表明:该微阀具有良好的开关性能和耐用性。     

A power-free deposited microbead plug-based microfluidic chip for whole-blood immunoassay

We present a deposited microbead plug (DMBP)-based microfluidic chip capable of performing plasma extraction and on-chip immunoassay. The DMBP used as a porous blood filter provides pure blood plasma without the contamination of blood cells or beads. Capillary-driven flow eliminates the requirement of external pumps. The human IgG and goat anti-human IgG sample-to-answer assay was performed in this chip within 600 s using only a 10 μl whole-blood sample. This easy-to-use, rapid, inexpensive, and disposable DMBP-based chip holds a great promise for point-of-care application.     

Application of metal film protection to microfluidic chip fabrication using CO2 laser ablation

The CO₂ laser ablation is a common technique for patterning the microchannels and holes used in microfluidic devices. However, the ablation process frequently results in an accumulation of resolidified material around the rims of the ablated features and a clogging of the base of the microchannel. In the article, these problems are resolved by means of a proposed metal-film-protected CO₂ laser ablation technique. In the approach, the substrate is patterned with a thin metallic mask prior to the ablation process and the mask is then stripped away once the ablation process is complete. The feasibility of the proposed approach is demonstrated by fabricating two micromixers with Y-shaped and T-shaped microchannels, respectively. It shows that for a designed channel width of 100 μm, the metallic mask reduces the ablated channel width from 268 to 103 μm. Moreover, the bulge height around the rims of the channel is reduced from 8.3 to <0.2 μm. Finally, the metallic mask also prevents clogging in the intersection regions of the two devices. The experimental mixing results obtained using red and green pigment dyes confirm the practical feasibility of the proposed approach.     

Design,simulation and experiment of electroosmotic microfluidic chip for cell sorting

A microfluidic cell sorting chip has been developed using micromachining technology, where electroosmotic flow (EOF) is exploited to drive and switch cells. For this electroosmotically driven system, it is found that the effect of induced hydrostatic pressure caused by unequal levels in solution reservoirs is not negligible. In this work, the numerical simulation of EOF and opposing pressure induced flow in microchannels is presented and the velocity profiles in the microchannels are measured experimentally using microparticle imaging velocimetry (PIV) system. The result shows that the final resulting velocity is the superposition of the two flows. A total volume of 0.305 μl is transported in the 50 μm microchannel and the back flow occurs after 240 s transportation. The task of sorting cells is realized at the switching structure by adjusting the electric fields in the microchannels. The performance of the cell sorting chip is optimized by investigating the effect of different switching structures. A Y-junction switching structure with 90° switching angle is highly recommended with simulated leakage distance of 53 μm and switching time of 8 ms.     

An integrated silicon sensor with microfluidic chip for monitoring potassium and pH

We present ion-sensitive field effect transistor-based sensors, integrated with a microfluidic chip, for monitoring pH and potassium cations. The sensor is strategically located at the base of a well so that the response time of the device depends both on the mean flow through the device and the diffusion coefficient of the analyte being monitored. This would enable monitoring of ions in the presence of larger molecules. The dependence of the device response time on diffusive transport of analytes was examined through a numerical study of the flow field and the passive diffusion of a chemical species. The predicted device response time was compared with the experimental measurements and reasonable agreement found. The general dependence of device response time on geometry, flow rate, and analyte diffusion coefficient was derived. These devices can be used with biological fluids where monitoring of pH and cations provide vital information about the well-being of patients.     

A facile strategy to integrate robust porous aluminum foil into microfluidic chip for sorting particles

High efficiency integration of functional microdevices into microchips is crucial for broad microfluidic applications. Here, a device-insertion and pressure sealing method was proposed to integrate robust porous aluminum foil into a microchannel for microchip functionalization which demonstrate the advantage of high efficient foil microfabrication and facile integration into the microfluidic chip. The porous aluminum foil with large area (10 × 10 mm²) was realized by one-step femtosecond laser perforating technique within few minutes and its pores size could be precisely controlled from 3 μm to millimeter scale by adjusting the laser pulse energy and pulse number. To verify the versatility and flexibility of this method, two kinds of different microchips were designed and fabricated. The vertical-sieve 3D microfluidic chip can separate silicon dioxide (SiO₂) microspheres of two different sizes (20 and 5 μm), whereas the complex stacking multilayered structures (sandwich-like) microfluidic chip can be used to sort three different kinds of SiO₂ particles (20, 10 and 5 μm) with ultrahigh separation efficiency of more than 92%. Furthermore, these robust filters can be reused via cleaning by backflow (mild clogging) or disassembling (heavy clogging).     

A method of water pretreatment to improve the thermal bonding rate of PMMA microfluidic chip

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.     

Particle focusing in a contactless dielectrophoretic microfluidic chip with insulating structures

The focusing of biological and synthetic particles in microfluidic devices is a crucial step for the construction of many microstructured materials as well as for medical applications. The present study examines the feasibility of using contactless dielectrophoresis (cDEP) in an insulator-based dielectrophoretic (iDEP) microdevice to effectively focus particles. Particles 10?μm in diameter were introduced into the microchannel and pre-confined hydrodynamically by funnel-shaped insulating structures near the inlet. The particles were repelled toward the center of the microchannel by the negative DEP forces generated by the insulating structures. The microchip was fabricated based on the concept of cDEP. The electric field in the main microchannel was generated using electrodes inserted into two conductive micro-reservoirs, which were separated from the main microchannel by 20-μm-thick insulating barriers made of polydimethylsiloxane (PDMS). The impedance spectrum of the thin insulating PDMS barrier was measured to investigate its capacitive behavior. Experiments employing polystyrene particles were conducted to demonstrate the feasibility of the proposed microdevice. Results show that the particle focusing performance increased with increasing frequency of the applied AC voltage due to the reduced impedance of PDMS barriers at high frequencies. When the frequency was above 800?kHz, most particles were focused into a single file. The smallest width of focused particles distributed at the outlet was about 13.1?μm at a frequency of 1?MHz. Experimental results also show that the particle focusing performance improved with increasing applied electric field strength and decreasing inlet flow rate. The usage of the cDEP technique makes the proposed microchip mechanically robust and chemically inert.     

Identification of respiratory pathogen Bordetella Pertussis using integrated microfluidic chip technology

Integrated PCR–CE chip technology has immense potential to be applied in clinical diagnostics. In this work we demonstrate the application of our integrated PCR–CE chip for the detection of the respiratory pathogen Bordetella pertussis. A series of experiments with varying cell concentrations (200,000–2 cfu) were performed to obtain the analytical detection limits of the chip. We find that the chip technology is well suited for sensitive detection of Bordetella pertussis, using genetic material from less than even 2 cfu. We also utilized an off-chip real-time PCR method to compare and validate our on-chip approach.     

基于微流体芯片结构的PDMS二次倒模工艺研究

研究了用于制作微流体芯片结构的聚二甲基硅氧烷(PDMS)与PDMS之间的倒模方法。首先,通过使用同一个微流体芯片模具倒出多个相同的PDMS负模结构;接着分别在各负模结构上溅射不同种类、不同厚度的金属,然后再对溅射过金属的负模上浇铸PDMS并固化以进行二次倒模,最后对二次倒模出的PDMS微流体结构表面粘连、结构完整性、尺寸等进行观测,从而通过比较得到倒模溅射所需的最佳金属和溅射金属薄膜的最优厚度。此方法倒出的PDMS微流体结构完整性好,不仅提出了一种全新的用于PDMS倒模的方法,而且解决了PDMS与PDMS之间直接倒模时所遇到的相互粘连和结构撕裂等难题。     

ITO薄膜微流体芯片的温控系统设计

设计了一种用于氧化铟锡(ITO)薄膜基材微流体芯片的恒温控制系统。系统采用数字温度传感器采集ITO薄膜温度,USB 2.0接口通信。用户通过PC机可实时监测微流体芯片温度变化情况,设定目标温度,以及存储温度数据。系统采用改进增量式PID控制算法实现温度控制,控制精度可达±0.2℃。