纸基过氯乙烯树脂微流控亚硝酸根离子检测片的研制

基于滤纸上过氯乙烯树脂栏选择性通过亚硝酸根离子, 结合微流控分析装置设计, 研制成纸基过氯乙烯树脂微流控亚硝酸根离子检测芯片. 采用该微流控亚硝酸根离子检测芯片测定了亚硝酸盐样品, 线性范围和检测限分别为70～1500 μmol/L 和48 μmol/L. 该微流控亚硝酸根离子检测芯片已成功应用于水样和食品中亚硝酸盐测定, 结果满意.     

Portable smartphone-based microfluidic electrochemical immunosensor for ultrasensitive detection of alpha-fetoprotein in human serum

Rapid and accurate tracing of biomarkers is essential for early detecting and diagnosing of cancer. Therefore, a valid and convenient strategy needs to be developed for efficient monitoring of cancer biomarkers. Herein, we constructed a portable microfluidic electrochemical immunosensor based on three-dimensional reduced graphene oxide (3D rGO) doped with gold nanoparticles (Au NPs) for ultrasensitive determination of alpha-fetoprotein (AFP). The designed microfluidic chip, with the advantages of small injection volume, detachable structure and high integration, was fabricated by 3D printing, which only needed 9 μL of reagent to realize the high sensitivity detection. In addition, the 3D Au NPs-rGO composites with high specific surface area and electrons transfer capacity can effectively increase electroactive sites and enhance electrochemical signals. Benefiting from these features, the 3D Au NPs-rGO microfluidic electrochemical immunochip showed a wide detection range between 0.1 pg/mL–200 ng/mL and a best detection limit of 0.045 pg/mL with the high sensitivity of 175.008 μA (ng/mL)⁻¹ cm⁻². Meanwhile, the proposed immunosensor exhibited reliable AFP detection in human serum samples, which demonstrated that this portable smartphone-based microfluidic electrochemical immunosensor hold great promises in clinical detection and huge potential in personalized healthcare.     

Microfluidic refractometer with micro-image defocusing

We herein report on a novel micro-refractometer with a self-calibration function. A micro-image defocusing (μ-ID) technique using optical path separation via a three-pinhole aperture is adopted to measure refractive index (RI). In order to achieve self-calibration, the microfluidic device is designed to have a self-calibration region into which reference fluids with known RIs are injected, as well as a measurement region into which a sample fluid is injected. In this way, the RI of the sample fluid is calculated automatically. In order to demonstrate the application of our proposed micro-refractometer, certified RI liquids with RIs of 1.300, 1.400, 1.450, 1.500, 1.550, 1.600, and 1.700 were used. The experimental demonstration described herein shows that the measured RIs have a deviation of less than 0.0009 with an uncertainty of ±0.001 refractive index unit (RIU) compared with their certified values.     

Microfluidic chip accomplishing self-fluid replacement using only capillary force and its bioanalytical application

A polymer microfluidic chip accomplishing automated sample flow and replacement without external controls and an application of the chip for bioanalytical reaction were described. All the fluidic operations in the chip were achieved by only natural capillary flow in a time-planned sequence. For the control of the capillary flow, the geometry of the channels and chambers in the chip was designed based on theoretical considerations and numerical simulations. The microfluidic chip was made by using polymer replication techniques, which were suitable for fast and cheap fabrication. The test for a biochemical analysis, employing an enzyme (HRP)-catalyzed precipitation reaction, exhibited a good performance using the developed chip. The presented microfluidic method would be applicable to biochemical lab-on-a-chips with integrated fluid replacement steps, such as affinity elution and solution exchange during biosensor signaling.     

Microfluidics technology for manipulation and analysis of biological cells

Analysis of the profiles and dynamics of molecular components and sub-cellular structures in living cells using microfluidic devices has become a major branch of bioanalytical chemistry during the past decades. Microfluidic systems have shown unique advantages in performing analytical functions such as controlled transportation, immobilization, and manipulation of biological molecules and cells, as well as separation, mixing, and dilution of chemical reagents, which enables the analysis of intracellular parameters and detection of cell metabolites, even on a single-cell level. This article provides an in-depth review on the applications of microfluidic devices for cell-based assays in recent years (2002–2005). Various cell manipulation methods for microfluidic applications, based on magnetic, optical, mechanical, and electrical principles, are described with selected examples of microfluidic devices for cell-based analysis. Microfluidic devices for cell treatment, including cell lysis, cell culture, and cell electroporation, are surveyed and their unique features are introduced. Special attention is devoted to a number of microfluidic devices for cell-based assays, including micro cytometer, microfluidic chemical cytometry, biochemical sensing chip, and whole cell sensing chip.     

Parylene to silicon nitride bonding for post-integration of high pressure microfluidics to CMOS devices

High pressure-rated channels allow microfluidic assays to be performed on a smaller footprint while keeping the throughput, thanks to the higher enabled flow rates, opening up perspectives for cost-effective integration of CMOS chips to microfluidic circuits. Accordingly, this study introduces an easy, low-cost and efficient method for realizing high pressure microfluidics-to-CMOS integration. First, we report a new low temperature (280 °C) Parylene-C wafer bonding technique, where O(2) plasma-treated Parylene-C bonds directly to Si(3)N(4) with an average bonding strength of 23 MPa. The technique works for silicon wafers with a nitride surface and uses a single layer of Parylene-C deposited only on one wafer, and allows microfluidic structures to be easily formed by directly bonding to the nitride passivation layer of the CMOS devices. Exploiting this technology, we demonstrated a microfluidic chip burst pressure as high as 16 MPa, while metal electrode structures on the silicon wafer remained functional after bonding.     

Interconnected ordered nanoporous networks of colloidal crystals integrated on a microfluidic chip for highly efficient protein concentration

We report a controllable method to fabricate silica colloidal crystals at defined position in microchannel of microuidic devices using simple surface modification. The formed PCs (photonic crystals) in microfluidic channels were stabilized by chemical cross-linking of Si-O-Si bond between neighboring silica beads. The voids among colloids in PCs integrated on microfluidic devices form interconnected nanoporous networks, which show special electroosmotic properties. Due to the "surface-charge induced ion depletion effect" mechanism, FITC-labeled proteins can be efficiently and selectively concentrated in the anodic boundary of the ion depletion zone. Using this device, about 10(3) - to 10(5)-fold protein concentration was achieved within 10 min. The present simple on chip protein concentration device could be a potential sample preparation component in microfluidic systems for practical biochemical assays.     

Digital droplet immunoassay based on a microfluidic chip with magnetic beads for the detection of prostate-specific antigen

Sensitive biomarker detection techniques are beneficial for both disease diagnosis and postoperative examinations. In this study, we report an integrated microfluidic chip designed for the immunodetection of prostate-specific antigens (PSAs). The microfluidic chip is based on the three-dimensional structure of quartz capillaries. The outlet channel extends to 1.8 cm, effectively facilitating the generation of uniform droplets ranging in size from 3 to 50 μm. Furthermore, we successfully immobilized the captured antibodies onto the surface of magnetic beads using an activator, and we constructed an immunosandwich complex by employing biotinylated antibodies. A key feature of this microfluidic chip is its integration of microfluidic droplet technology advantages, such as high-throughput parallelism, enzymatic signal amplification, and small droplet size. This integration results in an exceptionally sensitive PSA detection capability, with the detection limit reduced to 7.00 ± 0.62 pg/mL.     

Centrifugally-driven sample extraction, preconcentration and purification in microfluidic compact discs

Centrifugally-driven microfluidic compact discs (μ-CDs) have attracted significant interest within the analytical science community in the past decade, with the primary focus on the potential of such platforms for performing parallel and/or multiplex biological assays and further application in biomedical diagnostics. More recently, μ-CD-based devices were also applied to environmental analysis as platforms for multi-sample extraction and transportation, prior to off-disc analysis in the laboratory. This review critically summarizes recent developments in μ-CD platforms for sample extraction, preconcentration, fractionation and purification in bioanalytical and environmental applications. We also summarize the common methods employed in the fabrication of μ-CD platforms. Further, we discuss preparation of stationary phases in microfluidic channels embedded in μ-CDs, as applications of μ-CDs in sample extraction are generally based on enclosed series of extraction phases and microcolumns.     

Fuel cell-powered microfluidic platform for lab-on-a-chip applications

The achievement of a higher degree of integration of components--especially micropumps and power sources--is a challenge currently being pursued to obtain portable and totally autonomous microfluidic devices. This paper presents the integration of a micro direct methanol fuel cell (μDMFC) in a microfluidic platform as a smart solution to provide both electrical and pumping power to a Lab-on-a-Chip system. In this system the electric power produced by the fuel cell is available to enable most of the functionalites required by the microfluidic chip, while the generated CO(2) from the electrochemical reaction produces a pressure capable of pumping a liquid volume through a microchannel. The control of the fuel cell operating conditions allows regulation of the flow rate of a liquid sample through a microfluidic network. The relation between sample flow rate and the current generated by the fuel cell is practically linear, achieving values in the range of 4-18 μL min(-1) while having an available power between 1-4 mW. This permits adjusting the desired flow rate for a given application by controlling the fuel cell output conditions and foresees a fully autonomous analytical Lab-on-a-Chip in which the same device would provide the electrical power to a detection module and at the same time use the CO(2) pumping action to flow the required analytes through a particular microfluidic design.     

集成核酸提取的实时荧光PCR微全分析系统

集成核酸提取的实时荧光PCR微全分析系统将核酸提取、PCR扩增与实时荧光检测进行整合,在同一块微流控芯片上实现了核酸分析过程的全自动和全封闭,具有试剂用量少、分析速度快、操作简便等优点。本研究采用微机械加工技术制作集成核酸提取微流控芯片的阳极模,使用组合模具法和注塑法制作具有3D通道的PDMS基片,与玻璃基底通过等离子体键合封装成集成核酸提取芯片。构建了由微流体速度可调节(0~10 mL/min)的驱动控制装置、温控精度可达0.1℃的TEC温控平台、CCD检测功能模块等组成的微全分析系统。以人类血液裂解液为样品,采用硅胶膜进行芯片上核酸提取。系统根据设置好的时序自动执行,以2 mL/min的流体驱动速度完成20μL裂解液上样、清洗;以1 mL/min的流体驱动速度完成DNA洗脱,抽取PCR试剂与之混合注入到反应腔。提取的基因组DNA以链上内参基因GAPDH为检测对象,并以传统手工提取为对照,在该系统平台上进行PCR扩增和熔解曲线分析实验。片上PCR扩增结果显示,扩增曲线明显,Ct值分别为25.3和26.9。扩增产物进行熔解曲线分析得到的熔解温度一致,均为89.9℃。结果表明,此系统能够自动化、全封闭的在微流控芯片上完成核酸提取、PCR扩增与实时定量分析。     

A nanoliter rotary device for polymerase chain reaction

Polymerase chain reaction (PCR) has revolutionized a variety of assays in biotechnology. The ability to implement PCR in disposable and reliable microfluidic chips will facilitate its use in applications such as rapid medical diagnostics, food control testing, and biological weapons detection. We fabricated a microfluidic chip with integrated heaters and plumbing in which various forms of PCR have been successfully demonstrated. The device uses only 12 nL of sample, one of the smallest sample volumes demonstrated to date. Minimizing the sample volume allows low power consumption, reduced reagent costs, and ultimately more rapid thermal cycling.     

Assay for molecular transport across gap junction channels in one-dimensional cell arrays

Transport across gap junction channels (GJCs) between neighboring cells is critical to synchronizing cell's electrical and metabolic activities and maintaining cell homeostasis. Here we present a non-invasive microfluidic method to measure molecular diffusion across GJCs in multiple 1D cell arrays in real time. Using the chip, selective loading of a membrane permeant fluorescence dye (carboxyfluorescein) in Normal Rat Kidney (NRK) cells shows that the dye was able to diffuse through three cells along single cell chains in ～35 minutes. Application of 100 μM 2-aminoethoxydiphenyl borate (2-APB) reversibly inhibits connexin-43 gap junctions in NRK cells; 0.8 mM 1-heptanol inhibits the diffusion partially. The method offers rapid exchange of reagents, enabling sequential screening of multiple gap junction specific drugs with only one preparation of cells. It is capable of measuring gap junction mediated diffusion between single cells.     

Microfluidic platform for combinatorial synthesis in picolitre droplets

This paper presents a droplet-based microfluidic platform for miniaturized combinatorial synthesis. As a proof of concept, a library of small molecules for early stage drug screening was produced. We present an efficient strategy for producing a 7 × 3 library of potential thrombin inhibitors that can be utilized for other combinatorial synthesis applications. Picolitre droplets containing the first type of reagent (reagents A(1), A(2), …, A(m)) were formed individually in identical microfluidic chips and then stored off chip with the aid of stabilizing surfactants. These droplets were then mixed to form a library of droplets containing reagents A(1-m), each individually compartmentalized, which was reinjected into a second microfluidic chip and combinatorially fused with picolitre droplets containing the second reagent (reagents B(1), B(2), …, B(n)) that were formed on chip. The concept was demonstrated with a three-component Ugi-type reaction involving an amine (reagents A(1-3)), an aldehyde (reagents B(1-7)), and an isocyanide (held constant), to synthesize a library of small molecules with potential thrombin inhibitory activity. Our technique produced 10(6) droplets of each reaction at a rate of 2.3 kHz. Each droplet had a reaction volume of 3.1 pL, at least six orders of magnitude lower than conventional techniques. The droplets can then be divided into aliquots for different downstream screening applications. In addition to medicinal chemistry applications, this combinatorial droplet-based approach holds great potential for other applications that involve sampling large areas of chemical parameter space with minimal reagent consumption; such an approach could be beneficial when optimizing reaction conditions or performing combinatorial reactions aimed at producing novel materials.     

Surface enhanced Raman spectroscopy for microfluidic pillar arrayed separation chips

Numerous studies have addressed the challenges of implementing miniaturized microfluidic platforms for chemical and biological separation applications. However, the integration of real time detection schemes capable of providing valuable sample information under continuous, ultra low volume flow regimes has not fully been addressed. In this report we present a chip based chromatography system comprising of a pillar array separation column followed by a reagent channel for passive mixing of a silver colloidal solution into the eluent stream to enable surface enhanced Raman spectroscopy (SERS) detection. Our design is the first integrated chip based microfluidic device to combine pressure driven separation capability with real time SERS detection. With this approach we demonstrate the ability to collect distinctive SERS spectra with or without complete resolution of chromatographic bands. Computational fluidic dynamic (CFD) simulations are used to model the diffusive mixing behaviour and velocity profiles of the two confluent streams in the microfluidic channels. We evaluate the SERS spectral band intensity and chromatographic efficiency of model analytes with respect to kinetic factors as well as signal acquisition rates. Additionally, we discuss the use of a pluronic modified silver colloidal solution as a means of eliminating contamination generally caused by nanoparticle adhesion to channel surfaces.     

An integrated digital microfluidic chip for multiplexed proteomic sample preparation and analysis by MALDI-MS

To realize multiplexed sample preparation on a digital microfluidic chip for high-throughput Matrix Assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS), several fluidic functions need to be integrated. These include the generation of multiple droplets from a reservoir and parallel in-line sample purification. In this paper, we develop two critical new functions in handling protein solutions and standard proteomic reagents with electrowetting-on-dielectric (EWOD) actuation, leading to an integrated chip for multiplexed sample preparation for MALDI-MS. The first is a voltage sequence designed to generate a series of droplets from each of the three reservoirs--proteomic sample, rinsing fluid, and MALDI reagents. It is the first time that proteomic reagents have been dispensed using EWOD in an air (as opposed to oil) environment. The second is a box-in-box electrode pattern developed to allow droplet passing over dried sample spots, making the process of in-line sample purification robust for parallel processing. As a result, parallel processing of multiple sample droplets is demonstrated on the integrated EWOD-MALDI-MS chip, an important step towards high-throughput MALDI-MS. The MS results, collected directly from the integrated devices, are of good quality, suggesting that the tedious process of sample preparation can be automated on-chip for MALDI-MS applications as well as other high-throughput proteomics applications.     

Flexible microfluidic cloth-based analytical devices using a low-cost wax patterning technique

This paper describes the fabrication of microfluidic cloth-based analytical devices (μCADs) using a simple wax patterning method on cotton cloth for performing colorimetric bioassays. Commercial cotton cloth fabric is proposed as a new inexpensive, lightweight, and flexible platform for fabricating two- (2D) and three-dimensional (3D) microfluidic systems. We demonstrated that the wicking property of the cotton microfluidic channel can be improved by scouring in soda ash (Na(2)CO(3)) solution which will remove the natural surface wax and expose the underlying texture of the cellulose fiber. After this treatment, we fabricated narrow hydrophilic channels with hydrophobic barriers made from patterned wax to define the 2D microfluidic devices. The designed pattern is carved on wax-impregnated paper, and subsequently transferred to attached cotton cloth by heat treatment. To further obtain 3D microfluidic devices having multiple layers of pattern, a single layer of wax patterned cloth can be folded along a predefined folding line and subsequently pressed using mechanical force. All the fabrication steps are simple and low cost since no special equipment is required. Diagnostic application of cloth-based devices is shown by the development of simple devices that wick and distribute microvolumes of simulated body fluids along the hydrophilic channels into reaction zones to react with analytical reagents. Colorimetric detection of bovine serum albumin (BSA) in artificial urine is carried out by direct visual observation of bromophenol blue (BPB) colour change in the reaction zones. Finally, we show the flexibility of the novel microfluidic platform by conducting a similar reaction in a bent pinned μCAD.     

微流控芯片流动注射气体扩散分离光度测定系统的研究

提出了纳升级进样量的微流控芯片流动注射气体扩散分离光度检测系统. 制作三层结构微流控芯片, 在玻璃片上加工微反应通道, 用聚二甲基硅氧烷[Poly(dimethylsiloxane), PDMS]加工气体渗透膜和具有接收气体微通道的底片, 实现了生成气体的化学反应、气-液分离和检测在同一微芯片上的集成化. 采用缝管阵列纳升流动注射进样系统连续进样, 用吸光度法测定NH+4以验证系统性能. 结果表明， 该系统对NH+4的检出限为140 μmol/L(3σ), 峰高精度为3.7%(n=9). 在进样时间12 s、注入载流48 s和每次进样消耗200 nL试样条件下, 系统分析通量可达60样/h. 若加大样品量到800 nL, 使接收溶液停流1 min, 该系统对NH+4的检出限可达到35 μmol/L(3σ), 但分析通量降低到20样/h.     

Extraction,amplification and detection of DNA in microfluidic chip-based assays

This review covers three aspects of PCR-based microfluidic chip assays: sample preparation, target amplification, and product detection. We also discuss the challenges related to the miniaturization and integration of each assay and make a comparison between conventional and microfluidic schemes. In order to accomplish these essential assays without human intervention between individual steps, the micro-components for fluid manipulation become critical. We therefore summarize and discuss components such as microvalves (for fluid regulation), pumps (for fluid driving) and mixers (for blending fluids). By combining the above assays and microcomponents, DNA testing of multi-step bio-reactions in microfluidic chips may be achieved with minimal external control. The combination of assay schemes with the use of micro-components also leads to rapid methods for DNA testing via multi-step bioreactions. Contains 259 references. Figure

A graphical presentation of main PCR assays: DNA extraction from raw sample, target amplification by PCR and final product detection in conventional bench-top lab and miniaturized microfluidic chip.     

Integrated electrofluidic circuits: pressure sensing with analog and digital operation functionalities for microfluidics

Microfluidic technology plays an essential role in various lab on a chip devices due to its desired advantages. An automated microfluidic system integrated with actuators and sensors can further achieve better controllability. A number of microfluidic actuation schemes have been well developed. In contrast, most of the existing sensing methods still heavily rely on optical observations and external transducers, which have drawbacks including: costly instrumentation, professional operation, tedious interfacing, and difficulties of scaling up and further signal processing. This paper reports the concept of electrofluidic circuits - electrical circuits which are constructed using ionic liquid (IL)-filled fluidic channels. The developed electrofluidic circuits can be fabricated using a well-developed multi-layer soft lithography (MSL) process with polydimethylsiloxane (PDMS) microfluidic channels. Electrofluidic circuits allow seamless integration of pressure sensors with analog and digital operation functions into microfluidic systems and provide electrical readouts for further signal processing. In the experiments, the analog operation device is constructed based on electrofluidic Wheatstone bridge circuits with electrical outputs of the addition and subtraction results of the applied pressures. The digital operation (AND, OR, and XOR) devices are constructed using the electrofluidic pressure controlled switches, and output electrical signals of digital operations of the applied pressures. The experimental results demonstrate the designed functions for analog and digital operations of applied pressures are successfully achieved using the developed electrofluidic circuits, making them promising to develop integrated microfluidic systems with capabilities of precise pressure monitoring and further feedback control for advanced lab on a chip applications.