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.     

键合方法对聚二甲基硅氧烷液滴型微流控芯片的影响

液滴型微流控芯片表面性质是影响其性能的重要因素. 研究了不同键合方法对基于聚二甲基硅氧烷(PDMS)的液滴型微流控芯片微管道表面性质的影响, 并分别观察和评价了不同键合方法所制作液滴型微流控芯片应用于制备油包水和水包油两种液滴分散体系的效果. 结果显示热扩散键合方法适用于制作油包水型PDMS液滴型微流控芯片, 而等离子键合方法制作的PDMS芯片适于形成水包油型的液滴分散体系.     

Lithographic patterning on polydimethylsiloxane surfaces using polydimethylglutarimide

We present a method for high fidelity lithographic patterning on polydimethylsiloxane (PDMS) surfaces employing traditional cleanroom equipment and commercially available materials that overcomes previous problems in PDMS processing. To illustrate this method, an electrostatically actuated microfluidic pump and rectangular diffraction gratings were fabricated on PDMS.     

Analysis of pressure-driven air bubble elimination in a microfluidic device

We report an analysis of pressure-driven bubble elimination for a gas-permeable microfluidic device. In this study, we described bubble elimination in a microfluidic device employing a gas permeation model and calculated the removal efficiency of bubbles. The correction factor for the simplified model was estimated with respect to the applied pressure. Based on the established model, the required time to remove a trapped bubble with a certain area was shown to be within an error of 11.58% by comparison with experimental results. Exploiting the model equation, we were able to completely remove the air bubbles appearing during the process of filling a microfluidic device with an aqueous solution.     

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.     

Electrochemical wettability switches gate aqueous liquids in microfluidic systems

We demonstrate a simple low-voltage technique for gating the flow of aqueous liquids in microfluidic systems employing the electrochemically-controlled surface energy of the conjugated polymer poly(3-hexylthiophene).     

Electrochemical Immunosensing Chip Using Selective Surface Modification,Capillary‐Driven Microfluidic Control,and Signal Amplification by Redox Cycling

A sensitive electrochemical immunosensing chip is presented by employing (i) selective modification of protein‐resistant surfaces; (ii) fabrication of a stable Ag/AgCl reference electrode; (iii) capillary‐driven microfluidic control; (iv) signal amplification by redox cycling along with enzymatic reaction. Purely capillary‐driven microfluidic control is combined with electrochemical sandwich‐type immunosensing procedure. Selective modification of the surfaces is achieved by chemical reactivity‐controlled patterning and electrochemical deposition. Fluidic control of the immunosensing chip is achieved by spontaneous capillary‐driven flows and passive washing. The detection limit for mouse IgG in the immunosensing chip is 10 pg/mL.     

Specific Transport of Target Molecules by Motor Proteins in Microfluidic Channels

Direct transport powered by motor proteins can alleviate the challenges presented by miniaturization of microfluidic systems. There have been several recent attempts to build motor‐protein‐driven transport systems based on simple capturing or transport mechanisms. However, to achieve a multifunctional device for practical applications, a more complex sorting/transport system should be realized. Herein, the proof of concept of a sorting device employing selective capture of distinct target molecules and transport of the sorted molecules to different predefined directions is presented. By combining the bottom‐up functionality of biological systems with the top‐down handling capabilities of micro‐electromechanical systems technology, highly selective molecular recognition and motor‐protein‐based transport is integrated in a microfluidic channel network.     

Dynamic drag force based on iterative density mapping: A new numerical tool for three‐dimensional analysis of particle trajectories in a dielectrophoretic system

Dielectrophoresis is a widely used means of manipulating suspended particles within microfluidic systems. In order to efficiently design such systems for a desired application, various numerical methods exist that enable particle trajectory plotting in two or three dimensions based on the interplay of hydrodynamic and dielectrophoretic forces. While various models are described in the literature, few are capable of modeling interactions between particles as well as their surrounding environment as these interactions are complex, multifaceted, and computationally expensive to the point of being prohibitive when considering a large number of particles. In this paper, we present a numerical model designed to enable spatial analysis of the physical effects exerted upon particles within microfluidic systems employing dielectrophoresis. The model presents a means of approximating the effects of the presence of large numbers of particles through dynamically adjusting hydrodynamic drag force based on particle density, thereby introducing a measure of emulated particle–particle and particle–liquid interactions. This model is referred to as “dynamic drag force based on iterative density mapping.” The resultant numerical model is used to simulate and predict particle trajectory and velocity profiles within a microfluidic system incorporating curved dielectrophoretic microelectrodes. The simulated data are compared favorably with experimental data gathered using microparticle image velocimetry, and is contrasted against simulated data generated using traditional “effective moment Stokes‐drag method,” showing more accurate particle velocity profiles for areas of high particle density.     

重力驱动多相层流分离离子选择性电极检测集成化微流控芯片系统

将微流控芯片多相层流分离技术与离子选择性电极检测技术联用,利用重力驱动的芯片多相层流分离系统,在线净化生物(血液)试样.同时,在芯片上加工微离子选择性电极进行待测物的在线检测,实现整体分析系统的芯片集成化,并将其用于血样中K⁺的测定.对5.5×10^-3mol/L钾溶液5次平行测定的相对标准偏差(RSD)为5.6%,检出限为6.8×10^-5mol/L,线性范围10^-4～10^-1mol/L.     

Multilevel microfluidics via single-exposure photolithography

This communication reports a new method to form multilevel features in a single layer of SU-8 photoresist to facilitate the generation of 3D microfluidic chips. The method utilizes the spatial dependence of diffracted light intensity to selectively overexpose masked regions of photoresist and requires only a UV light source and a single transparency mask. 3D structures are formed within microfluidic channels using this selective overexposure method, with feature sizes being determined by the exposure dose and mask feature sizes. The dimensions of the internal features and the microfluidic channels can be varied independently according to these parameters, and any number of different heights can be obtained in a single exposure step. The method provides a simple means of forming 3D microfluidic structures with integrated features, including mixing structures, flow stabilization ridges, and separation weirs to increase the capabilities of microfluidic chips in a variety of microchemical applications.     

An Immobilized‐Dirhodium Hollow‐Fiber Flow Reactor for Scalable and Sustainable C−H Functionalization in Continuous Flow

A scalable flow reactor is demonstrated for enantioselective and regioselective rhodium carbene reactions (cyclopropanation and C?H functionalization) by developing cascade reaction methods employing a microfluidic flow reactor system containing immobilized dirhodium catalysts in conjunction with the flow synthesis of diazo compounds. This allows the utilization of the energetic diazo compounds in a safe manner and the recycling of the dirhodium catalysts multiple times. This approach is amenable to application in a bulk‐scale synthesis employing asymmetric C?H functionalization by stacking multiple fibers in one reactor module. The products from this sequential flow–flow reactor are compared with a conventional batch reactor or flow–batch reactor in terms of yield, regioselectivity, and enantioselectivity.     

Trapping of DNA by dielectrophoresis

Under suitable conditions, a DNA molecule in solution will develop a strong electric dipole moment. This induced dipole allows the molecule to be manipulated with field gradients, in a phenomenon known as dielectrophoresis (DEP). Pure dielectrophoretic motion of DNA requires alternate current (AC) electric fields to suppress the electrophoretic effect of the molecules net charge. In this paper, we present two methods for measuring the efficiency of DEP for trapping DNA molecules as well as a set of quantitative measurements of the effects of strand length, buffer composition, and frequency of the applied electric field. A simple configuration of electrodes in combination with a microfluidic flow chamber is shown to increase the concentration of DNA in solution by at least 60-fold. These results should prove useful in designing practical microfluidic devices employing this phenomenon either for separation or concentration of DNA.     

Microfluidic sensing devices employing in situ-formed liquid crystal thin film for detection of biochemical interactions

Although biochemical sensing using liquid crystals (LC) has been demonstrated, relatively little attention has been paid towards the fabrication of in situ-formed LC sensing devices. Herein, we demonstrate a highly reproducible method to create uniform LC thin film on treated substrates, as needed, for LC sensing. We use shear forces generated by the laminar flow of aqueous liquid within a microfluidic channel to create LC thin films stabilized within microfabricated structures. The orientational response of the LC thin films to targeted analytes in aqueous phases was transduced and amplified by the optical birefringence of the LC thin films. The biochemical sensing capability of our sensing devices was demonstrated through experiments employing two chemical systems: dodecyl trimethylammonium bromide (DTAB) dissolved in an aqueous solution, and the hydrolysis of phospholipids by the enzyme phospholipase A(2) (PLA(2)).     

Rapid discovery of potent siRNA-containing lipid nanoparticles enabled by controlled microfluidic formulation

The discovery of potent new materials for in vivo delivery of nucleic acids depends upon successful formulation of the active molecules into a dosage form suitable for the physiological environment. Because of the inefficiencies of current formulation methods, materials are usually first evaluated for in vitro delivery efficacy as simple ionic complexes with the nucleic acids (lipoplexes). The predictive value of such assays, however, has never been systematically studied. Here, for the first time, by developing a microfluidic method that allowed the rapid preparation of high-quality siRNA-containing lipid nanoparticles (LNPs) for a large number of materials, we have shown that gene silencing assays employing lipoplexes result in a high rate of false negatives (~90%) that can largely be avoided through formulation. Seven novel materials with in vivo gene silencing potencies of >90% at a dose of 1.0 mg/kg in mice were discovered. This method will facilitate the discovery of next-generation reagents for LNP-mediated nucleic acid delivery.     

Automated analysis of single stem cells in microfluidic traps

We report a reliable strategy to perform automated image cytometry of single (non-adherent) stem cells captured in microfluidic traps. The method rapidly segments images of an entire microfluidic chip based on the detection of horizontal edges of microfluidic channels, from where the position of the trapped cells can be derived and the trapped cells identified with very high precision (>97%). We used this method to successfully quantify the efficiency and spatial distribution of single-cell loading of a microfluidic chip comprised of 2048 single-cell traps. Furthermore, cytometric analysis of trapped primary hematopoietic stem cells (HSC) faithfully recapitulated the distribution of cells in the G1 and S/G2-M phase of the cell cycle that was measured by flow cytometry. This approach should be applicable to automatically track single live cells in a wealth of microfluidic systems.     

Polymer microfluidic devices

Since the introduction of lab-on-a-chip devices in the early 1990s, glass has been the dominant substrate material for their fabrication (J. Chromatogr. 593 (1992) 253; Science 261 (1993) 895). This is primarily driven by the fact that fabrication methods were well established by the semiconductor industry, and surface properties and derivatization methods were well characterized and developed by the chromatography industry among others. Several material properties of glass make it a very attractive material for use in microfluidic systems; however, the cost of producing systems in glass is driving commercial producers to seek other materials. Commercial manufacturers of microfluidic devices see many benefits in employing plastics that include reduced cost and simplified manufacturing procedures, particularly when compared to glass and silicon. An additional benefit that is extremely attractive is the wide range of available plastic materials which allows the manufacturer to choose materials' properties suitable for their specific application. In this article, we present a review of polymer-based microfluidic systems including their material properties, fabrication methods, device applications, and finally an analysis of the market that drives their development.     

Generation of concentration gradient by controlled flow distribution and diffusive mixing in a microfluidic chip

We have developed a simple method to generate a concentration gradient in a microfluidic device. This method is based on the combination of controlled fluid distribution at each intersection of a microfluidic network by liquid pressure and subsequent diffusion between laminas in the downstream microchannel. A fluid dynamic model taking into account the diffusion coefficient was established to simulate the on-chip flow distribution and diffusion. Concentration gradients along a distance of a few hundred micrometers were generated in a series of microchannels. The gradients could be varied by carefully regulating the liquid pressure applied to the sample injection vials. The observed concentration gradients of fluorescent dyes generated on the microfluidic channel are consistent with the theoretically predicted results. The microfluidic design described in this study may provide a new tool for applications based on concentration gradients, including many biological and chemical analyses such as cellular reaction monitoring and drug screening.     

A multi-functional electrochemical sensing system using microfluidic technology for the detection of urea and creatinine

This study presents a new microfluidic system capable of precise measurements of two important biomarkers, urea and creatinine, automatically. In clinical applications, high levels of these two biomarkers are early indicators of nephropathy or renal failure and should be monitored on a regular basis. The microfluidic system is composed of a microfluidic chip, a control circuit system, a compressed air source and several electromagnetic valves to form a handheld system. The microfluidic chip is fabricated by using micro-electromechanical systems and microfluidic techniques comprising electrochemical sensor arrays and polydimethylsiloxane-based microfluidic structures such as micropumps/micromixers, normally closed valves and microchannels. The microfluidic system performs a variety of critical processes including sample pretreatment, mixing, transportation and detection on a single chip. The experimental results show that the entire procedure takes approximately 40 min, which is much faster than the traditional method (more than 6 h). Furthermore, the total sample volume consumed in each operation is only 0.1 mL, which is significantly less than that required in a large system (5 mL). The developed automatic microfluidic system may provide a powerful platform for further clinical applications.