一种基于微流控芯片技术的流式细胞计数系统

采用聚二甲基硅氧烷（PDMS）材料制作微流控流式细胞计数芯片,利用负压驱动与鞘液夹流技术实现样品的水力聚焦,达到了10μm的样品聚焦宽度。基于激光诱导荧光技术,制作了小型化的检测装置。以488nm固体激光器为光源,激光束以45°方向穿过一个水平狭缝,以线光源形式汇聚到微流控芯片的检测区域,并与微通道垂直交叉,细胞样品的荧光信号通过光电倍增管收集。整个分析系统结构简单,操作方便,灵敏度高,可初步实现细胞的计数。     

光纤型微流控电泳芯片的研制

介绍了一种光纤型微流控电泳芯片,该芯片主要由两部分组成:多模光纤,PDMS基片和盖片.利用二次曝光技术制作出芯片的模具;通过浇注的方法制成电泳芯片;实现了在PDMS上制作深度不同的微流控沟道和光纤沟道,使光纤与微流控沟道能够方便地对准;利用异硫氰酸酯荧光素考察了系统的性能,最小检测浓度达到1.3×10-7mol/L,信噪比S/N=5.     

集成毛细管电泳芯片的设计

利用ANSYS软件对集成毛细管电泳芯片微沟道内样品流动情况进行模拟,获得了不同进样模式下微沟道的结构与流体流速之间的关系,并以此为依据对芯片整体结构参数进行设计:毛细管沟道最终尺寸为宽度16μm,深度10μm,有效分离长度为3.5cm的圆角转弯形沟道,从而确定整个芯片设计。     

PDMS用加窗方式快速复制微结构

提出了一种微流控芯片中的制作方法,此方法可以复制现有芯片的任意结构,可用于实验室原有芯片的修复和整合.用窗口的方法提取结构,可排除芯片上相邻结构的干扰,得到表面光滑整齐的新芯片.特别适用于复制目前软光刻工艺尚未达到的特微结构和三维结构芯片.实验制作出的聚二甲基硅氧烷(PDMS)芯片沟道长30μm,宽5μm,深5μm,显微镜下观察芯片表面光滑,窗口内沟道性质复制良好,窗口边缘与表面之间具有明显的陡变.     

基于纳米磁珠技术的新型微全分析DNA芯片的研究

在微全分析系统的研究中,样品提取及DNA分析技术是非常重要的一个环节.也是目前国内外研究的热点之一.文中介绍了一种新型的基于单芯片的样品制备和扩增方法.采用多层微加工技术制作SU-8模具,通过注模成型,制作出有立体微柱结构的PDMS(聚二甲基硅氧烷)芯片,在芯片微池内填充超顺磁性磁珠,利用固相提取(solid phase extraction,SPE)法,将细胞裂解、DNA提取、PCR反应等功能集成在一个PDMS芯片上.整个流程快速有效,操作简便且易于芯片系统集成,提取产物可以不必洗脱,直接作为下一步PCR反应的模板,在同一芯片上进行扩增反应,实现了样品预处理、DNA提取和PCR扩增的集成.     

聚二甲基硅氧烷微流控芯片的制备

采用印刷电路板技术加工出芯片模具,以聚二甲基硅氧烷(PDMS)为材料制作出微流控芯片。该芯片由基片和盖片组成,微流控沟道位于基片上,深度和宽度分别为75μm和100μm,由盖片对其进行密封。考察了有绝缘漆模具和无绝缘漆模具制作的芯片的电泳分离情况。在该PDMS微流控芯片上对用异硫氰酸酯荧光素标记的氨基酸进行了电泳分离,当信噪比S/N=3时,最小检测浓度达到0.8×10-11mol/L。     

微沟道内两相流速比对液滴形成的影响

研究了流聚焦微沟道内不同两相流速比对单分散性液滴形成的影响.不相混容的两相系统能够快速、周期性地形成液滴,液滴的形态和生成率随着油相速度的变化而改变.研究采用模拟软件COMSOL Mutiphysics,模拟了不同流速下液滴的形成过程,并通过实验进行了验证,从流体动力学的角度解释了其物理机制.所得结论为在流聚焦微沟道内获得分散性良好且大小可控的液滴提供了理论和数据支持.     

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。     

一种用于生化传感检测的压电式行波微流泵的研究

为了减少生化传感器中样品的消耗,基于行波原理,本文设计了一种新型的压电式微流泵.首先,理论证明了行波的产生机理,并用流体仿真软件Fluent进行了验证;其次,设计并制作了锯齿沟道和直沟道两种结构的微流泵,在压电双晶片阵列的驱动下,测量了这两种微流泵在不同频率和电压下的特性.结果表明锯齿形沟道结构的压电式行波微流泵性能更...     

微米印制技术中PDMS印章工艺的研究

采用Dow Corning公司的作为制作PDMS(Polydimethylsiloxan聚二甲基硅氧烷)为原材料,通过4英寸晶元腐蚀切割制成的Si印章模板,进而制作成相同尺寸的聚合物测试样品。实验研究了在不同温度,混合比例,凝固时间下所得到PDMS印章样品的结构强度,得到相对结构稳定,强度较高PDMS印章的制备工艺。并在此基础上研究印章结构(例如倾角,表面平整度或结构尺寸等)对所印制结构的影响,分析了制作硅模板和使用其生产PDMS印章工艺过程中参数对结构变化的各种影响,有利于得到更加精确的印制结构.     

Three-dimensional hydrodynamic focusing in polydimethylsiloxane (PDMS) microchannels

This paper presents a generalization of the hydrodynamic focusing technique to three-dimensions. Three-dimensional (3-D) hydrodynamic focusing offers the advantages of precision positioning of molecules in both vertical and lateral dimensions and minimizing the interaction of the sample fluid with the surfaces of the channel walls. In an ideal approach, 3-D hydrodynamic focusing could be achieved by completely surrounding the sample flow by a cylindrical sheath flow that constrains the sample flow to the center of the channel in both the lateral and the vertical dimensions. We present here design and simulation, 3-D fabrication, and experimental results from a piecewise approximation to such a cylindrical flow. Two-dimensional (2-D) and 3-D hydrodynamic focusing chips were fabricated using micromolding methods with polydimethylsiloxane (PDMS). Three-dimensional hydrodynamic focusing chips were fabricated using the "membrane sandwich" method. Laser scanning confocal microscopy was used to study the hydrodynamic focusing experiments performed in the 2-D and 3-D chips with Rhodamine 6G solution as the sample fluid and water as the sheath fluid.     

Parameters affecting the shape of a hydrodynamically focused stream

Even at low Reynolds numbers, momentum can impact the shape of hydrodynamically focused flow. Both theoretical and experimental characterization of hydrodynamic focusing in microchannels at Reynolds numbers ≤25 revealed the important parameters that affect the shape of the focused layer. A series of symmetric and asymmetric microfluidic channels with two converging streams were fabricated with different angles of confluence at the junction. The channels were used to study the characteristics of Y-type microchannels for flow-focusing. Computational analysis and experimental results gathered using confocal microscopy and particle image velocimetry indicated that the orientation of the sheath and the sample stream inlets, as well as the absolute flow velocities, determine the curvature in the concentration distribution of the focused stream. Decreasing the angle of confluence between sheath and sample, as well as reducing the overall Reynolds number, resulted in a flat interface between sheath and focused fluids. Alignment of the faster flowing sheath fluid channel with the main channel also reduced the inertial effects and produced a focused stream with a flat concentration profile. Control over the shape of the focused stream is important in many biosensors and lab-on-a-chip devices that rely on hydrodynamic focusing for increased detection sensitivity.     

An integrated flow-cell for full sample stream control

In this study, we present a novel three-dimensional hydrodynamic sheath flow chip that allows full control of a sample stream. The chip offers the possibility to steer each of the four side sheath flows individually. The design of the flow-cell exhibits high flexibility in creating different sample stream profiles (width and height) and allows navigation of the sample stream to every desired position inside the microchannel (vertical and horizontal). This can be used to bring the sample stream to a sensing area for analysis, or to an area of actuation (e.g. for cell sorting). In addition, we studied the creation of very small sample stream diameters. In microchannels (typically 25 × 40 μm2), we created sample stream diameters that were five to ten times smaller than the channel dimensions, and the smallest measured sample stream width was 1.5 μm. Typical flow rates are 0.5 μl/min for the sample flow and around 100 μl/min for the cumulated sheath flows. The planar microfabricated chip, consisting of a silicon–glass sandwich with an intermediate SU-8 layer, is much smaller (6 × 9 mm2) than the previously presented sheath flow devices, which makes it also cost-effective. We present the chip design, fluidic simulation results and experiments, where the size, shape and position of the sample stream have been established by laser scanning confocal microscopy and dye intensity analysis.     

Three-dimensional hydrodynamic flow and particle focusing using four vortices Dean flow

We present a three-dimensional (3D) hydrodynamic focusing device built on a single-layer platform using single sheath flow. Despite the simple structure and operation, the device not only achieves narrow focusing of a sample fluid or particles but also switches the cross-sectional size and lateral position of the sample stream. The focusing mechanism utilizes four Dean vortices generated in a high-speed flow through a curved channel. Theoretical calculations, numerical simulations, and an experimental study demonstrated that the device could focus microparticles that resemble human platelets in terms of particle size and density in a single-stream manner. Further simulation study suggested that the device could focus most cell sizes used in flow cytometry with a throughput of 200,000 cells s^?1. In addition, the device can function as a 3D liquid-core/liquid-cladding (L2) optical waveguide by introducing a core liquid with a refractive index higher than that of the cladding.     

An optimal three-dimensional focusing technique for micro-flow cytometers

This study presents a novel three-dimensional (3-D) hydrodynamic focusing technique for micro-flow cytometers. In the proposed approach, the sample stream is initially compressed in the horizontal direction by two sheath flows such that it is constrained in the central region of the microchannel. The sample stream is then focused in the vertical direction by a second pair of sheath flows and subsequently passes over a micro-weir structure positioned directly beneath an optical detection system. The microchannel configuration and operational parameters are optimized by performing a series of numerical simulations to examine the effects on the sample stream distribution of the vertical and horizontal focusing ratios, the entrance angle of the second set of sheath flow channels, and the width and depth of the second set of sheath flow channels. The results indicate that the horizontal and vertical sheath flows successfully constrain the sample stream within a narrow, well-defined region of the microchannel. Furthermore, the micro-weir structure results in the separation of the cells/particles in the vertical direction and ensures that they flow in a sequential fashion through the detection region of the microchannel and can therefore be reliably counted. It is shown that the 3-D focusing technique can achieve a focused sample stream width of between 6 and 15 μm given an appropriate value of the horizontal focusing ratio. Thus, the viability of the microflow cytometer for the counting and detection of individual biological cells is confirmed.     

集成惯性聚焦结构的介电泳微流控芯片的粒子连续分离

设计并制造了一种带有惯性聚焦结构的介电泳微流控芯片,以实现不同介电性质的粒子连续分离.采用MEMS工艺制作了介电泳微流控芯片:通道入口侧壁设置一对梯形结构使经过的粒子受惯性升力的作用聚焦到通道两侧;通道底部光刻一组夹角为90°的倾斜叉指电极产生非均匀电场,利用介电泳力和流体曳力的合力使通道两侧不同的粒子发生角度不同的偏转进入不同通道,从而实现分离.将酵母菌细胞和聚苯乙烯小球作为实验样本,分析了流速和交流电压对分离的影响,确定了二者分离的最优条件并进行分离.实验结果表明,将电导率为20μS/cm的样本溶液以5μL/min的流速注入到通道中,施加6 Vp-p、10 kHz的正弦信号,酵母菌细胞沿电极运动至夹角处后沿通道中心排出,聚苯乙烯小球沿通道两侧排出,成功实现分离,平均分离效率达92.8％、平均分离纯度达90.7％.     

Multi-helical micro-channels for rapid generation of drops of water in oil

High throughput generation of microscopic mono-dispersed droplets of one liquid into the continuous flow of another is important for large number of engineering and biomedical applications. However, meeting conflicting demands of both uniformity of size and high rate of droplet generation have been a difficult task to be accomplished in conventional systems. We have attempted to address this problem by designing a novel multi-helical micro-channel which we have used to generate water droplets in a continuous flow of oil. The channel consists of three or more helical flow paths joined along their contour length forming a single channel with inherently asymmetric geometry. Helix angle and radius are found to be two additional geometric parameters which influence different drop break-up regimes. We have shown that both time period of generation of drops and the droplet size can be minimized by suitably altering the helix angle. A scaling law has been derived to rationalize these results.     

Optimization and application of dry film photoresist for rapid fabrication of high-aspect-ratio microfluidic devices

Fabrication of high-aspect-ratio PDMS microfluidic devices with conventional SU-8 based soft photolithography is challenging, and often, the thickness of the master from which PDMS replicas are molded is non-uniform. Here, we present an optimized, low cost, fast prototyping microfabrication technique to make deep (up to 500 μm) and high-aspect-ratio (up to 10) microfluidic channels by producing masters by laminating a single or multiple layers of a thin dry film photoresist onto metal wafers. In particular, we explore the required exposure energy for different film thicknesses as well as the highest achievable channel depths and aspect ratios. The homogeneity of the depth of PDMS channels formed using these masters is quantified and found to be remarkably uniform over distances of 20 mm or more. The importance of the processing parameters, such as the exposure energy and development time on final feature size, wall angle, and channel aspect ratio, is investigated. In addition, we report some failure cases, the potential reasons, and strategies for making optimized devices. Potentially, deep microfluidic channels with a wide range of aspect ratios can be used to make long, homogenous separation devices that can be used in cell sorting, filtration, and flow cytometry. We believe the protocols we outline here will be of great utility to the microfluidics community.     

Micro-optofluidic switch realized by 3D printing technology

This paper presents a PDMS micro-optofluidic chip that allows a laser beam to be driven directly toward a two-phase flow stream in a micro-channel while at the same time automatically, detecting the slug’s passage and stirring the laser light, without the use of any external optical devices. When the laser beam interacts with the microfluidic flow, depending on the fluid in the channel and the laser angle of incidence, a different signal level is detected. So a continuous air–water segmented flow will generate a signal that switches between two values. The device consists of a T-junction, which generates the two-phase flow, and three optical fiber insertions, which drive the input laser beam toward a selected area of the micro-channel and detects the flow stream. Three micro-channel sections of different widths were considered: 130, 250, 420 μm and the performance of the models was obtained by comparing ray-tracing simulations. The master of the device has been realized by 3D printing technology and a protocol which realizes the PDMS chip is presented. The static and dynamic characterizations, considering both single flows and two-phase flows, were carried out, and in spite of the device’s design simplicity, the sensitivity of the system to capture changes in the segmented flows and to stir the laser light in different directions was fully confirmed. The experimental tests show the possibility of obtaining satisfactory results with channel diameters in the order of 200 μm.