Droplet microfluidic preparation of au nanoparticles-coated chitosan microbeads for flow-through surface-enhanced Raman scattering detection

An integrated microfluidic device was fabricated to enable on-chip droplet forming, trapping, fusing, shrinking, reaction and producing functional microbeads for a flow-through single bead-based molecule detection. Dielectrophoresis (DEP) force was used to transport target polymer droplets into different predefined microwells, where the droplets were fused through electrocoalescence to form a new one with a desired diameter. In a continuous water loss process with water diffusion to oil phase, the polymer droplet was shrunken and solidified to form a polymer microbead. For a demonstration, Au nanoparticles-coated chitosan microbeads were in situ fabricated through droplet trapping, fusion and shrinking, followed by synthesis of Au nanoparticles on the microbead surface via a photoreduction process. The produced Au nanoparticle/chitosan microbead embedded in the microwell resulted in a highly sensitive, flow-through surface-enhanced Raman scattering (SERS) detection of Rhodamine 6G (R6G). This work successfully demonstrates an integrated droplet based lab-on-a chip and its application to fabricate an extremely high-throughput single bead based detection platform.     

A microfluidic-based dynamic microarray system with single-layer pneumatic valves for immobilization and selective retrieval of single microbeads

A simple yet effective dynamic bead-based microarray is necessary for multiplexed high-throughput screening applications in the fields of biology and chemistry. This paper introduces a microfluidic-based dynamic microbead array system using pneumatically driven elastomeric valves integrated with a microchannel in a single polydimethylsiloxane (PDMS) layer that performs the following functions: single-microbead arraying with loading and trapping efficiencies of 100 %, sequential microbead release for selective retrieval of microbeads of interest, and rapid microarray resettability (<1 s). The key feature is the utilization of an elastomeric membrane as a valve for trapping and releasing single microbeads; this membrane is deformable depending on the applied pneumatic pressure, thereby simply providing a dual trap-and-release function. We propose an effective single-microbead-trapping mechanism based on a dynamic flow-change network and a mathematical model as the design criterion of a trapping site. A sequential microbead release technique via a multistep “release-retrap-and-repeat” method was developed for the selective retrieval of trapped microbeads with a simple configuration consisting of a single PDMS layer and a simple macro-to-micro connection. The proposed dynamic microbead array could be a powerful tool for high-throughput multiplex bead-based drug screening or disease diagnosis.     

Development of microfluidic alginate microbead generator tunable by pulsed airflow injection for the microencapsulation of cells

Recently, microbead generation and microencapsulation of cells using microfluidic technology have been actively pursued for various applications. However, most of the proposed systems are not only technically demanding, but might also be harmful to the encapsulated cells. To tackle these issues, this study reports a microfluidic alginate microbead generator consisting of a polydimethylsiloxane (PDMS) microfluidic chip and an integrated quartz microcapillary tube. The working principle is based on the use of a pulsed airflow to segment a continuous alginate suspension flow to form suspension fragments in a microchannel and then alginate microbeads when they were delivered out the microfluidic system to a sterile calcium chloride solution through a microcapillary tube. In this study, the alginate suspension fragments with varied sizes in the microchannel can be generated either by modulating the alginate suspension flow rate or the pulsation frequency of airflow injection. By fine tuning the size of them, the alginate microbeads can be generated in a size-controllable manner. Results showed that alginate microbeads with the size ranging from 150 to 370 μm in diameter can be generated at the suspension flow rate and airflow injection frequency ranges of 2–4 μl/min and 0.6–35 Hz, respectively. Besides, the alginate microbeads generated by the system were tested with excellent size uniformity (CV: 3.1–5.1%). Moreover, its application for the microencapsulation of chondrocytes in alginate microbeads was also demonstrated with high cell viability (96 ± 2%). As a whole, the proposed device has paved an alternative route to perform alginate microbead generation or microencapsulation of cells in a simple, continuous, controllable, uniform, cell friendly, and less contaminated manner.     

Selective position of individual cells without lysis on a circular window array using dielectrophoresis in a microfluidic device

We trapped individual cells between two circular windows using negative dielectrophoretic (DEP) force and then sequentially trapped them inside circular windows by positive DEP force without electrical lysis in a microfluidic device. Three parameters, (1) the transmembrane potential that determines the lysis of a cell, (2) individual cell size that affects the trapped position accuracy of the cell, and (3) the Clausius–Mossotti (CM) factor that decides the trapped efficiency of the cell, were characterized experimentally and numerically in this sequential cell trapping technique. In this characterization, we confirmed that the swap rate of applied voltage frequency, size similarity between the cell and circular window, and instantaneous change rate of Re(f _CM) as a function of frequency were important factors in determining the selective position of individual cells without lysis. Our results provide useful suggestions for designing the structure of microfluidic DEP devices and optimizing variables required to manipulate individual cell trapping using both negative and positive DEP forces.     

Stepwise gray-scale light-induced electric field gradient for passive and continuous separation of microparticles

This article presents a gray-scale light-induced dielectrophoresis (GS-LIDEP) method that induces the lateral displacements normal to the through-flow for continuous and passive separation of microparticles. In general, DEP force only can affect the particles within very local areas due to the electric field is exponentially decayed by the distance away from the electrodes. Unlike with conventional LIDEP, a broad-ranged electrical field gradient can easily be created by GS pattern illumination, which induces DEP forces with two directions for continuous separation of particles to their specific sub-channels. Candia albicans were effectively guided to the specific outlet with the efficiency of 90% to increase the concentration of the sample below the flow rate of 0.6?μl/min. 2 and 10?μm polystyrene particles can also be passively and well separated using the multi-step GS pattern through positive and negative DEP forces, respectively, under an applied voltage of 36?V_p–p at the frequency of 10?kHz. GS-LIDEP generated a wide-ranged DEP force that is capable of working on the entire area of the microchannel, and thus the mix of particles can be passively and continuously separated toward the opposite directions by the both positive and negative GS-LIDEP forces. This simple, low cost, and flexible separation/manipulation platform could be very promising for many applications, such as in-field detections/pretreatments.     

Design of new microchannel to reduce applied voltage for microparticles separation using dielectrophoresis method

This paper presents a new structure of microchannel in order to reduce the applied voltage using dielectrophoresis (DEP). DEP is one of the most popular techniques to separate microparticles which needs an electric field in microfluidic devices. In this study, the AC-DEP sidewall electrodes are used. The novelty of this research is to change the outlet microchannel size which effectively reduces applied voltage. In previous work, in order to separate particles with 3.5 and 4 µm diameters, 4.5 V was needed. In new design, we keep all effective parameters constant and change one of the outlet microchannel size from 50 to 60, 70 and 80 µm. Therefore, in order to separate the microparticles, we need only 3, 2 and 1.3 V, respectively.

     

基于FPGA的剩余电压检测系统的设计

提出了一种高准确度低功耗的剩余电压检测方法。该测量装置通过过零检测电路获取工频同步信号,在工频交流峰值时刻切断待测设备的电源,由高输入阻抗的输入回路对待测设备的剩余电压进行取样;在NiosII的控制下,采用高速采样保持电路和高精度模数转换器实现设备掉电1 s和10 s后剩余电压的在线检测。实验证明该测量装置有较好的稳定性,测量准确度达到0.506%,满足测量要求。     

食物致病菌快速检测系统的设计与实现

设计了食物致病菌快速检测一体化系统。基于抗原-抗体特异性结合的原理,采用TiO2纳米线束为敏感元件设计微生物免疫传感器,以高集成度芯片AD5933设计阻抗检测电路来通过电化学阻抗谱法测量该传感器中TiO2纳米线束的阻抗变化量,实现了致病菌数量的快速检测。以大肠杆菌为例作为实验样本对检测一体化系统的性能进行测试,实验结果表明该检测一体化系统可以快速检测出食物中存在的大肠杆菌,检测周期约为1 h,系统的检测下限为4.5×102cfu/mL,传感器在扫描频率为1 000 Hz～10 000 Hz之间表现出来的重复性较好。     

A Programmable Biochip for the Applications of Trapping and Adaptive Multisorting Using Dielectrophoresis Array

The adaptive biochip integrating dielectrophoresis (DEP) traps and a programmable multisorting DEP array for the multisorting applications of biomolecules such as proteins and DNA is proposed and demonstrated in this paper. In this research, movable beads are used as the mobile probes to capture the target protein molecules. These beads are chemically modified and immobilized with p50 proteins in our demonstration. An array of micropyramid DEP traps with a good levitation control on the height of the beads is located at the upstream to enhance the hybridization function of the mobile probes. The sample solution mixed with Cy3-I-kappa-B-alpha complex is used in the demonstration. A programmable multisorting DEP array that is located at the downstream sorts out the hybridized beads, which are fluorescently labeled based on the fluorescent detection signals. The magnitude and direction of the DEP force that is applied to the beads with/without labeling fluorescence in the multisorting DEP array are controlled via the distribution of time-variant nonuniform electric fields. The voltage on the individual electrode of the multisorting DEP array is preprogrammed and controlled by a LabVIEW controller with fluorescence detection feedback signals. In contrast to the research of Manaresi et al. [IEEE J. Solid-State Circuits, vol. 38, no. 12, p. 2297, 2003], which was proposed for trapping and sorting beads and cells via Dent traps, to our knowledge, the design of this biochip with the hybridization enhancement via micropyramid DEP traps and the adaptive multisorting DEP array for the mobile probes has never been proposed and implemented to date.     

基于阻抗原理的磁弹性传感器测试仪设计

设计了一种基于阻抗原理的磁弹性传感器共振频率测试仪。系统集成了微控制器、交流激励信号发生单元、直流偏置信号发生单元和有效值检测电路单元,并通过RS-232串口总线实现与上位机之间的通信。交流激励信号电路采用压控电流源方式,避免了线圈阻抗变化对交流激励电流的影响。实验结果表明：测试仪可以快速检测磁弹性传感器的共振频率,稳定性好,精度高,系统操作简单,集成度高,能够满足磁弹性传感器研究中的检测要求。     

Automated microfluidic processing platform for multiplexed magnetic bead immunoassays

A microfluidic platform is presented which fully automates all incubation steps of a three-stage, multiplexed magnetic bead immunoassay, such as the Luminex^? xMAP technology. Magnetic actuation is used to transfer the microbeads between co-infused adjacent laminar flow streams to transport the beads into and out of incubation and wash solutions, with extended incubation channels to allow sufficient bead incubation times (1–30?min, commonly 5?min per stage) to enable high-sensitivity. The serial incubation steps of the immunoassay are completed in succession within the device with no operator interaction, and the continuous flow operation with magnetic bead transfer defines the incubation sequencing requiring no external fluidic controls beyond syringe pump infusion. The binding kinetics of the assay is empirically characterized to determine the required incubation times for specific assay sensitivities in the range 1?pg/ml to 100?ng/ml. By using a Luminex^? xMAP duplex assay, concurrent detection of IL-6 and TNF-α was demonstrated on-chip with a detection range 10?pg/ml to 1?ng/ml. This technology enables rapid automation of magnetic microbead assays, and has the potential to perform continuous concentration monitoring.     

基于微环形阵列电极的细胞分离富集芯片的设计与实验研究

根据介电泳操作原理,设计了微环形阵列电极结构,建立了细胞分离富集芯片模型,采用COMSOL软件分析微环形阵列电极的电场分布和介电泳力方向并确定了最大和最小电场强度的位置,利用ITO玻璃和PDMS制备了细胞分离富集芯片.通过酵母菌细胞的介电泳富集实验和酵母菌细胞与聚苯乙烯小球的分离富集实验,明确了酵母菌细胞的临界频率,实现了酵母菌细胞和聚苯乙烯小球的分离富集.结果显示,在溶液电导率为60μs/cm,交流信号电压为8Vp-p时,酵母菌细胞在1kHz~45kHz频率范围内做负介电泳运动并富集在环形内部,45kHz为酵母菌细胞的临界频率,在45kHz~10MHz频率范围内做正介电泳运动并富集在环形边缘;1.5MHz时聚苯乙烯小球做负介电泳运动并富集在环形内部,富集倍数达到11.66.     

A Model for Electrostatic Actuation in Conducting Liquids

This paper presents a generalized model that describes the behavior of micromachined electrostatic actuators in conducting liquids and provides a guideline for designing electrostatic actuators to operate in aqueous electrolytes such as biological media. The model predicts static actuator displacement as a function of device parameters and applied frequency and potential for the typical case of negligible double-layer impedance and dynamic response. Model results are compared to the experimentally measured displacement of electrostatic comb-drive and parallel-plate actuators and exhibit good qualitative agreement with experimental observations. The model is applied to show that the pull-in instability of a parallel-plate actuator is frequency dependent near the critical frequency for actuation and can be eliminated for any actuator design by tuning the applied frequency. In addition, the model is applied to establish a frequency-dependent theoretical upper bound on the voltage that can be applied across passivated electrodes without electrolysis.     

Bead-based polymerase chain reaction on a microchip

We present a bead-based approach to microfluidic polymerase chain reaction (PCR), enabling fluorescent detection and sample conditioning in a single microchamber. Bead-based PCR, while not extensively investigated in microchip format, has been used in a variety of bioanalytical applications in recent years. We leverage the ability of bead-based PCR to accumulate fluorescent labels following DNA amplification to explore a novel DNA detection scheme on a microchip. The microchip uses an integrated microheater and temperature sensor for rapid control of thermal cycling temperatures, while the sample is held in a microchamber fabricated from (poly)dimethylsiloxane and coated with Parylene. The effects of key bead-based PCR parameters, including annealing temperature and concentration of microbeads in the reaction mixture, are studied to achieve optimized device sensitivity and detection time. The device is capable of detecting a synthetically prepared section of the Bordetella pertussis genome in as few as 10 temperature cycles with times as short as 15?min. We then demonstrate the use of the procedure in an integrated device; capturing, amplifying, detecting, and purifying template DNA in a single microfluidic chamber. These results show that this method is an effective method of DNA detection which is easily integrated in a microfluidic device to perform additional steps such as sample pre-conditioning.     

微机检测信号的两种算法

由于某些微机受其字长的限制以及系统信号本身的变化，使得计算机对输入信号的实时快速面准确地处理受到影响，本文提出了一种适用于缺少乘、除法指令的八位机实时检测被控对象有功、无功、电压与电流的有效值（最大值）、阻抗的快速算法及一种检测信号频率变，校正采样周期的算法。     

新型改进锁相环FBD电流检测方法的实现

传统的谐波检测方法中,在电网电压畸变和频率偏移时,锁相环系统锁相不准确,影响谐波检测精度.在Fryze算法(FBD法)的基础上,提出利用改进的陷波器(LPN)锁相环(PLL)方法,该方法对两路线电压进行处理,再通过陷波器滤出畸变电压中的零序、负序分量和高次谐波,得到与基波正序电压同频同相的三相参考电压信号.理论推导和仿真结果表明,所提出的改进方法能有效地改善电网电压畸变时谐波电流的检测精度.     

A microfluidic device for rapid concentration of particles in continuous flow by DC dielectrophoresis

This article presents a microfluidic device (so called concentrator) for rapid and efficient concentration of micro/nanoparticles using direct current dielectrophoresis (DC DEP) in continuous fluid flow. The concentrator is composed of a series of microchannels constructed with PDMS-insulating microstructures to focus efficiently the electric field in the flow direction to provide high field strength and gradient. Multiple trapping regions are formed within the concentrator. The location of particle trapping depends on the strength of the electric field applied. Under the experimental conditions, both streaming movement and DEP trapping of particles simultaneously take place within the concentrator at different regions. The former occurs upstream and is responsible for continuous transport of the particles, whereas the latter occurs downstream and rapidly traps the particles delivered from upstream. The observation agrees with the distribution of the simulated electric field and DEP force. The performance of the device is demonstrated by successfully and effectively concentrating fluorescent nanoparticles. At the sufficiently high electric field, the device demonstrates a trapping efficiency of 100%, which means downstream DEP traps and concentrates all (100%) the incoming particles from upstream. The trapping efficiency of the device is further studied by measuring the fluorescence intensity of concentrated particles in the channel. Typically, the fluorescence intensity becomes saturated in Trap 1 by applying the voltage (400 V) for >2 min, demonstrating that rapid concentration of the nanoparticles (10⁷ particles/ml) is achieved in the device. The microfluidic concentrator described can be implemented in applications where rapid concentration of targets is needed such as concentrating cells for sample preparation and concentrating molecular biomarkers for detection.     

射频信号的S变换检测

本文针对射频(RF)信号的频率高、瞬变等特点,提出了一种基于S变换的射频信号检测方法。仿真结果表明,S变换具有很好的时频分析能力,能很好地分辩出射频信号的时频性能。     

Bioparticle separation and manipulation using dielectrophoresis

Manipulation and separation of micro-sized particles, particularly biological particles, using the dielectrophoretic (DEP) force is an emerging technique in MEMS technology. This paper presents a DEP-based microsystem for the selective manipulation and separation of bioparticles using dielectrophoretic effects. The microfabricated DEP device consists of a sandwich structure, in which a microchannel with electrode array lining on its bottom is sandwiched between the substrate and the glass lid. Dielectrophoretic behavior of polystyrene particles with diameter of 4.3 μm was studied. Both positive DEP and negative DEP were observed. Particles under positive DEP were attracted to the edges of the electrodes, while those under negative DEP were repelled away from the electrodes and levitated at certain height above the electrodes (within a proper range of frequencies of the electric field). Levitation height of the particles was measured. It was demonstrated that the levitation height of a specific particle strongly depends on the combined contributions of a number of parameters, such as the frequency of the electric field, dielectric properties of the particles and the surrounding medium. Different particles can be separated and manipulated on the basis of their difference in these parameters.     

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.