Utilizing a high fundamental frequency quartz crystal resonator as a biosensor in a digital microfluidic platform

We demonstrate the operation of a digital microfluidic lab-on-a-chip system utilizing Electro Wetting on Dielectrics (EWOD) as the actuation principle and a High Fundamental Frequency (HFF; 50?MHz) quartz crystal microbalance (QCM) resonator as a mass-sensitive sensor. In a first experiment we have tested the reversible formation of a phosphor-lipid monolayer of phospholipid vesicles out of an aqueous buffer suspension onto a bio-functionalized integrated QCM sensor. A binding of bio-molecules results in an altered mass load of the resonant sensor and a shift of the resonance frequency can be measured. In the second part of the experiment, the formation of a protein multilayer composed of the biomolecule streptavidin and biotinylated immunoglobulin G was monitored. Additionally, the macroscopic contact angle was optically measured in order to verify the bio-specific binding and to test the implications onto the balance of the surface tensions. Using these sample applications, we were able to demonstrate and to verify the feasibility of integrating a mass-sensitive QCM sensor into a digital microfluidic chip.     

Printing 3D microfluidic chips with a 3D sugar printer

This study demonstrated how to quickly and effectively print two-dimensional (2D) and three-dimensional (3D) microfluidic chips with a low-cost 3D sugar printer. The sugar printer was modified from a desktop 3D printer by redesigning the extruder, so the melting sugar could be extruded with pneumatic driving. Sacrificial sugar lines were first printed on a base layer followed by casting polydimethylsiloxane (PDMS) onto the layer and repeating. Microchannels were then printed in the PDMS solvent, microfluidic chips dropped into hot water to dissolve the sugar lines after the PDMS was solidified, and the microfluidic chips did not need further sealing. Different types of sugar utilized for printing material were studied with results indicating that maltitol exhibited a stable flow property compared with other sugars such as caramel or sucrose. Low cost is a significant advantage of this type of sugar printer as the machine may be purchased for only approximately $800. Additionally, as demonstrated in this study, the printed 3D microfluidic chip is a useful tool utilized for cell culture, thus proving the 3D printer is a powerful tool for medical/biological research.     

Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits

Reports the completion of four fundamental fluidic operations considered essential to build digital microfluidic circuits, which can be used for lab-on-a-chip or micro total analysis system (/spl mu/TAS): 1) creating, 2) transporting, 3) cutting, and 4) merging liquid droplets, all by electrowetting, i.e., controlling the wetting property of the surface through electric potential. The surface used in this report is, more specifically, an electrode covered with dielectrics, hence, called electrowetting-on-dielectric (EWOD). All the fluidic movement is confined between two plates, which we call parallel-plate channel, rather than through closed channels or on open surfaces. While transporting and merging droplets are easily verified, we discover that there exists a design criterion for a given set of materials beyond which the droplet simply cannot be cut by EWOD mechanism. The condition for successful cutting is theoretically analyzed by examining the channel gap, the droplet size and the degree of contact angle change by electrowetting on dielectric (EWOD). A series of experiments is run and verifies the criterion.     

数字微流控生化芯片多液滴稀释方法的研究

生化试验中如何将样品试剂配备过程转化成有效的数字生化芯片实现的协议,并给出相应的操作过程中的稀释/混合操作优化算法非常关键,是样品试剂配备过程的一个挑战。为减少操作步骤和节省药品,提出针对数字微流控生物芯片多液滴混合器稀释/混合操作优化算法,该算法允许多个液体参与混合分离操作,可以在误差允许范围内利用片上多液滴混合器用较少的操作步骤获得目标浓度的液滴。相对传统的两液滴混合方法,减少了稀疏/混合的步骤和稀释/混合时间,同时减少中间废弃液滴的数目。实验结果也表明可以在允许的误差范围内高效地进行混合/分离操作,获得目标浓度的液滴。     

Precision moulding of biomimetic disposable chips for droplet-based applications

In this study, we present a biomimetic approach to improve the stability and reproducibility of droplet generation processes and to reduce the adhesion of aqueous droplets to channel surfaces of microfluidic polymer chips. The hierarchical structure of the lotus leaf was used as a template for a partial laser structuring of the moulds that were used for casting the polymer chips. The hydrophobic wax layer of the lotus leaf was technologically replicated by coating the polymer chips using a plasma deposition process. The resulting microfluidic polymer chip surfaces reveal a topography and a surface free energy similar to those of the lotus leaf. Subsequent droplet-based microfluidic experiments were performed using a 2D flow focussing set-up. Droplets from both, serum-supplemented cell culture medium and anticoagulated human whole blood, could be generated stably and reproducibly using a fluorocarbon as continuous phase. The presented results illustrate the application potential of the lotus-leaf-like polymer chips in life sciences, e.g. in the field of personalised medicine.     

Digital microfluidic design and optimization of classic and new fluidic functions for lab on a chip systems

This paper deals with microfluidic studies for lab-on-a-chip development. The first goal was to develop microsystems immediately usable by biologists for complex protocol integrations. All fluid operations are performed on nano-liter droplet independently handled solely by electrowetting on dielectric (EWOD) actuation. A bottom-up architecture was used for chip design due to the development and validation of elementary fluidic designs, which are then assembled. This approach speeds up development and industrialization while minimizing the effort in designing and simplifying chip-fluidic programming. Dispensing reproducibility for 64 nl droplets obtained a CV below 3% and mixing time was only a few seconds. Ease of the integration was demonstrated by performing on chip serial dilutions of 2.8-folds, four times. The second part of this paper concerns the development of new innovative fluidic functions in order to extend EWOD-actuated digital fluidics’ capabilities. Experiments of particle dispensing by EWOD droplet handling are reported. Finally, work is shown concerning the coupling of EWOD actuation and magnetic fields for magnetic bead manipulation.     

基于微流控芯片的尿酸和抗坏血酸并行电化学检测研究

尿样和血样中的尿酸水平是诊断痛风等疾病的重要指标,传统检测方法存在时间长、需要其他辅助试剂等不足,开展了在微流控芯片上对尿酸进行电化学检测的研究：以碳纳米管修饰的丝网印刷电极片为检测单元,构建了PDMS微流控芯片。以微流控芯片为平台,采用微分脉冲伏安法（DPV）对尿酸和抗坏血酸分别进行检测,确定其原始峰值电位。最后,实验测试和分析比较了不同浓度尿酸和抗坏血酸对电化学检测信号的影响。研究结果表明：用DPV法分别检测尿酸和抗坏血酸,测得峰电流与样品浓度均有较好的线性度;从并行检测信号中能够分辨出尿酸和抗坏血酸的氧化峰位;尿酸和抗坏血酸对彼此的DPV峰位无明显影响,但对DPV电流峰值有一定抑制作用。     

EWOD microfluidic systems for biomedical applications

As the technology advances, a growing number of biomedical microelectromechanical systems (bio-MEMS) research involves development of lab-on-a-chip devices and micrototal analysis systems. For example, a portable instrument capable of biomedical analyses (e.g., blood sample analysis) and immediate recording, whether the patients are in the hospital or home, would be a considerable benefit to human health with an excellent commercial viability. Digital microfluidic (DMF) system based on the electrowetting-on-dielectric (EWOD) mechanism is an especially promising candidate for such point-of-care systems. The EWOD-based DMF system processes droplets in a thin space or on an open surface, unlike the usual microfluidic systems that process liquids by pumping them in microchannels. Droplets can be generated and manipulated on EWOD chip only with electric signals without the use of pumps or valves, simplifying the chip fabrication and the system construction. Microfluidic operations by EWOD actuation feature precise droplet actuation, less contamination risk, reduced reagents volume, better reagents mixing efficiency, shorter reaction time, and flexibility for integration with other elements. In addition, the simplicity and portability make the EWOD-based DMF system widely popular in biomedical or chemical fields as a powerful sample preparation platform. Many chemical and biomedical researches, such as DNA assays, proteomics, cell assays, and immunoassays, have been reported using the technology. In this paper, we have reviewed the recent developments and studies of EWOD-based DMF systems for biomedical applications published mostly during the last 5 years.     

Two-layer multiplexed peristaltic pumps for high-density integrated microfluidics

The integration and operation of a large number of components is needed to enable ever more complex and integrated chemical and biological processes on a single microfluidic chip. The capabilities of these chips are often limited by the maximum number of pumps and valves that can be controlled on a single chip, a limitation typically set by the number of pneumatic interconnects available from ancillary hardware. Here, we report a multiplexing approach that greatly reduces the number of external pneumatic connections needed for the operation of a large number of peristaltic pumps. The utility of the approach is demonstrated with a complex microfluidic network capable of generating and routing liquid droplets in a two-phase flow. We also report a set of design rules for the design and operation of multiplexed peristaltic pumps, based on a study of the effect of the number of valves per pump and the valve-to-valve distance on the performance of peristaltic pumps. The multiplexing approach reported here may find application in a wide range of microfluidic chips for chemical and biological applications, especially those that require the integration of many different operations on a single chip and those that need to perform similar operations massively in parallel, in sub-nanoliter volumes.     

Detection of Cellular Parameters Using a Microfluidic Chip-Based System

Lab-on-a-chip technology achieves a reduction of sample and reagent volume and automates complex laboratory processes. Here, we present the implementation of cell assays on a microfluidic platform using disposable microfluidic chips. The applications are based on the controlled movement of cells by pressure-driven flow inside networks of microfluidic channels. Cells are hydrodynamically focused and pass the fluorescence detector in single file. Initial applications are the determination of protein expression and apoptosis parameters. The microfluidic system allows unattended measurement of six samples per chip. Results obtained with the microfluidic chips showed good correlation with data obtained using a standard flow cytometer.     

Development of reel-to-reel microchip mounting system for fabrication of meter-long LED lighting tapes

We have developed a reel-to-reel microchip mounting system that continuously mounts LED chips and other microchips on meter-long flexible printed circuit board (PCB) tape for 1.2-m-long standard LED light tubes. Mounting microchips on meter-long PCBs is difficult because a large chip mounter is expensive and the chip positioning stage is difficult to move in a meter-wide area with an accuracy of hundreds of micrometers. Hence, we developed a new microchip mounting system that utilizes a small chip mounter and reel winding machines. The system repeatedly moves the long PCB tape by a certain length with the reel winding machines and mounts the chips on it. The PCB tape (which is 5 mm wide) is made by fabricating long PCB tapes which are 25 cm × 26.6 m through a roll-to-roll PCB process and slitting them into meter-long tapes. The reel-to-reel system repeatedly mounts chips by adjusting their positions through image processing of the copper wiring pattern on the PCBs. Our constructed system mounted 24 LED chips with a pitch of 5 cm with an accuracy of 0.082 mm to form a 1.2-m-long LED tape. The luminance of the tape is 12.4 lx at a distance of 1 m, which is the luminance of outdoor corridor lighting. Therefore, this system can be used for meter-long tape lighting.     

单泵控制聚焦流形态的微流控芯片的研制

研究一种单动力源、聚焦流形态可控的用于细胞排队的微流控芯片。建立了样品沟道与鞘流沟道不同长度比例、不同夹角的模型并进行了不同负压条件下聚焦流形态仿真,运用SPSS软件进行了回归分析并进行了模型优化。在芯片的微加工过程中,利用印刷电路板(PCB)制作了母板,以聚二甲基硅氧烷(PDMS)为芯片主要材料,制作了PDMS—PDMS,PDMS—玻璃及PCB—PDMS三种芯片。制作的芯片能够在单个动力源条件下控制聚焦流宽度,使不同大小的微粒及细胞呈单个排列流动。研究结果为分析不同尺寸的细胞而选择合适的样品流沟道与鞘流沟道长度、夹角等条件提供了依据,所制作的芯片也达到了廉价且实用的目的。     

微流体芯片在纤维成型方面的应用研究进展

微流体芯片可在微通道中控制、操作和检测复杂流体,具有尺寸小、效率高、集成度高、响应时间短、样品需量少等优点.除了在生物化学、有机合成、疾病检测等领域有广泛的应用之外,微流体芯片在纤维成型方面也有很大的应用潜力.在简介了微流体技术的基础上,比较了传统纺丝技术和微流体纺丝技术,综述了微流体芯片在即时纺丝、静电纺丝和蛋白质成...     

Rotating flow within a droplet actuated with AC EWOD

Electrowetting-on-dielectric (EWOD) is now used in numerous microsystems like digital lab-on-chips. This paper deals with a characteristic hydrodynamic flow appearing in droplets actuated by EWOD with AC voltage. In the coplanar electrode configuration, two pairs of vortex flows are observed to form in a droplet centred on the electrode gap. All experiments are performed in oil as ambient phase and flows in the droplet are analysed using fluorescent beads. At the same time, droplet oscillations induced by AC EWOD are also revealed under stroboscopic lighting. These experiments show that vortex location can be controlled by frequency actuation with fair degree of reproducibility.     

基于FPGA的微流控芯片电泳控制系统设计

设计一套基于FPGA的微流控芯片的电泳控制系统。该系统采用具有大量控制端口的FPGA作为系统的控制芯片,同时为了节约控制端口,选取串行控制的A／D与D／A芯片;采用USB2.0高速传输接口与上位机通信,满足了实施控制与数据上传的要求;采用VerilogHDL语言对芯片编程后,可同时对30个PCR芯片实施控制,另外还编写了基于Windows XP的驱动程序与控制软件。     

An integrated genetic analysis microfluidic platform with valves and a PCR chip reusability method to avoid contamination

Clinical diagnostics and genomic research often require performing numerous genetic tests. While microfluidic devices provide a low-cost alternative to such demands, integrated microfluidic devices are fabricated using expensive technology not always affordable for single use. However, carryover cross-contamination (CXC) concerns (i.e. either false positive or false negative PCR data) in PCR chips prevent reuse, defying much of the advantages of miniaturized systems developed using expensive MEMS processing. In this work, we present an integrated and reusable PCR–CE glass microfluidic chip capable of multi-chamber PCR and sequential CE, with emphasis on a unique chip reusability approach to avoid CXC. For reliable PCR, the surface of the chamber is re-configured from its virgin hydrophilic (CA < 20°) to hydrophobic (CA > 110°) by silanization. To then extend this silanization method as a chip reusability technique, the silanization coating is ‘stripped and re-silanized’ (SRS) to create a fresh coating prior to each successive PCR run. Experimental confirmation of the effectiveness of SRS method in avoiding the CXC is demonstrated using plasmid DNA and HIV-1 infected DNA samples. We also present passive plug microvalves incorporated in the chip to enable fluid/vapor retention during the PCR and controlled fluid flow from the PCR chamber to the CE section for further analysis.     

A fluidic interconnection system for polymer-based microfluidic devices

A microfabricated fluidic interconnection system for polymer-based microfluidic nebulizer chips is presented and discussed. The new interconnection mechanism can be used to make fluidic connection between external capillary and the polymer microfluidic chip. The connector mechanism was fabricated using a combination of mechanical milling and laser micromachining. Preliminary leakage tests were performed to demonstrate that the interconnection system is leak-free and pressure tests were performed to evaluate the burst pressure (maximum working pressure). The interconnection system has several advantages over commercially available Nanoport™ interconnection system. The new fluidic interconnection system implemented onto a microfluidic nebulizer chip was successfully tested for desorption electrospray ionization mass spectrometry applications. The performance of the chip using the new connector mechanism was excellent demonstrating the usability of the new connector mechanism.     

Electrowetting on polyimide and silicon substrates with high hysteresis

Microsystem Technologies - Electrowetting-on-dielectric (EWOD) with atypical liquid-substrate combinations has growing utility for a range of microfluidic devices. However, there are challenges to...     

Driving characteristics of the electrowetting-on-dielectric device using atomic-layer-deposited aluminum oxide as the dielectric

Electrowetting on dielectric (EWOD) is useful in manipulating droplets for digital (droplet-based) microfluidics, but its high driving voltage over several tens of volts has been a barrier to overcome. This article presents the characteristics of EWOD device with aluminum oxide (Al₂O₃, ε _r  ≈ 10) deposited by atomic layer deposition (ALD), for the first time as the high-k dielectric for lowering the EWOD driving voltage substantially. The EWOD device of the single-plate configuration was fabricated by several steps for the control electrode array of 1 mm × 1 mm squares with 50 μm space, the dielectric layer of 1,270 Å thick ALD Al₂O₃, the reference electrode of 20 μm wide line electrode, and the hydrophobic surface treatment by Teflon-AF coating, respectively. We observed the movement of a 2 μl water droplet in an air environment, applying a voltage between one of the control electrodes and the reference electrode in contact with the droplet. The droplet velocity exponentially depending on the applied voltage below 15 V was obtained. The measured threshold voltage to move the droplet was as low as 3 V which is the lowest voltage reported so far in the EWOD researches. This result opens a possibility of manipulating droplets, without any surfactant or oil treatment, at only a few volts by EWOD using ALD Al₂O₃ as the dielectric.     

Rapid prototyping of PMMA microfluidic chips utilizing a CO<Subscript>2</Subscript> laser

A commercially available CO₂ laser scriber is used to perform the direct-writing ablation of polymethyl-methacrylate (PMMA) substrates for microfluidic applications. The microfluidic designs are created using commercial layout software and are converted into the command signals required to drive the laser scriber in such a way as to reproduce the desired microchannel configuration on the surface of a PMMA substrate. The aspect ratio and surface quality of the ablated microchannels are examined using scanning electron microscopy and atomic force microscopy surface measurement techniques. The results show that a smooth channel wall can be obtained without the need for a post-machining annealing operation by performing the scribing process with the CO₂ laser beam in an unfocused condition. The practicality of the proposed approach is demonstrated by fabricating two microfluidic chips, namely a cytometer, and an integrating microfluidic chip for methanol detection, respectively. The results confirm that the proposed unfocused ablation technique represents a viable solution for the rapid and economic fabrication of a wide variety of PMMA-based microfluidic chips.