Lab-on-PCB-based micro-cytometer for circulating tumor cells detection and enumeration

Impedance-based microfluidic cytometer has been introduced to provide a companion diagnostic platform in biological cells analysis. In the conventional way, microfluidic impedance cytometer requires accurately patterning metal electrodes in the corresponding location on silicon/glass substrate, which is expensive and time-consuming. In this short communication, we demonstrate a disposable impedance-based microfluidic cytometer above the commercially available printed circuit board (PCB) with pre-deposited copper electrode, which is reusable. In this experiment, red blood cells (RBCs) and mixture of RBCs, white blood cells (WBCs), and circulating tumor cells (CTCs) are utilized to test the function of the proposed device, which indicated that it can differentiate the WBCs and CTCs from the mixture of the three types of cells. After each sample test, the upper microfluidic cytometer is disposed which shows the great commercial potential in point-of-care test for clinical application.     

Integrated microfluidic system for electrochemical sensing of glycosylated hemoglobin

This article reports a new miniature electrochemical detection system integrating a sample pretreatment device for fast detection of glycosylated hemoglobin (HbA_1C), which is a common indicator for diabetes mellitus. In this system, circular micropumps, normally closed microvalves, dielectrophoretic (DEP) electrodes, and electrochemical sensing electrode are integrated to perform several crucial processes. These processes include separation of red blood cells (RBCs), sample/reagent transportation, mixing, cell lysis, and electrochemical sensing. For the HbA_1C measurement, the RBCs are separated and are collected from whole human blood by using a positive DEP force generated by the DEP electrodes. The collected RBCs are then lysed to release HbA_1C for the subsequent electrochemical detection processes. Experimental data show that the RBCs are successfully separated and are collected using the developed system with a RBCs capture rate of 84.2%. The subsequent detection of HbA_1C is automatically completed by utilizing electrochemical sensing electrode. The microfluidic system only consumes a sample volume of 200 μl. The entire process is automatically performed within a short period of time (10 min). The development of this integrated microfluidic system may be promising for the clinical monitoring of diabetes mellitus.     

Experiments on opto-electrically generated microfluidic vortices

Strong microfluidic vortices are generated when a near-infrared (1,064 nm) laser beam is focused within a microchannel and an alternating current (AC) electric field is simultaneously applied. The electric field is generated from a parallel-plate, indium tin oxide (ITO) electrodes separated by 50 μm. We present the first μ-PIV analysis of the flow structure of such vortices. The vortices exhibit a sink-type behavior in the plane normal to the electric field and the flow speeds are characterized as a function of the electric field strength and biasing AC signal frequency. At a constant AC frequency of 100 kHz, the fluid velocity increases as the square of the electric field strength. At constant electric field strength fluid velocity does not change appreciably in the 30–50 kHz range and it decreases at larger frequencies (>1 MHz) until at approximately 5 MHz when Brownian motion dominates the movement of the 300 nm μ-PIV tracer particles. Presence of strongly focused laser beams in an interdigitated-electrode configuration can also lead to strong microfluidic vortices. When the center of the illumination is focused in the middle of an electrode strip, particles experiencing negative dielectrophoresis are carried towards the illumination and aggregate in this area.     

MEMS Electrostatic Actuation in Conducting Biological Media

We present design and experimental implementation of electrostatic comb-drive actuators in solutions of high conductivity relevant for biological cells. The actuators are operated in the frequency range 1-10 MHz in ionic and biological cell culture media, with ionic strengths up to 150 mmol/L. Typical displacement is 3.5 mum at an applied peak-to-peak signal of 5 V. Two different actuation schemes are presented and tested for performance at high frequency. A differential drive design is demonstrated to overcome the attenuation due to losses in parasitic impedances. The frequency dependence of the electrostatic force has been characterized in media of different ionic strengths. Circuit models for the electric double layer phenomena are used to understand and predict the actuator behavior. The actuator is integrated into a planar force sensing system to measure the stiffness of cells cultured on suspended structures.     

小球藻电介质电泳特性的实验研究

生物电介质电泳是指生物微粒在非均匀电场中，因介质极化而受电场力的作用，产生宏观位移运动的现象，本文运用针状电极，首次对小球藻的电介质电泳特性进行了研究。通过在５０Ｈｚ￣１ＭＨｚ频率范围内对小球藻细胞收集率频谱的测量，发现在１００Ｈｚ和１ＭＨｚ附近存在两个特征收集谱峰。还对影响小球藻收集率的因素进行了初步的实验研究。实验结果对于研制基于介质电泳的微生物传感器具有指导意义。     

测量油品含水量的电容式传感器机理

电容式传感器利用油与水介电常数差别较大的特性 ,可测出油品中水的质量分数。从物质分子结构的特征出发 ,探讨传感器的工作原理 ,分析在交变电场作用下水与油的极化过程以及交变电场频率对极化强度的影响。得出在交变电场频率为 10MHz时 ,油与水的介电常数差别最大 ,因而将 10MHz作为传感器的工作频率 ,可获得最高灵敏度     

Heat-shock protein-27, -70 and peroxiredoxin-II show molecular chaperone function in sickle red cells: Evidence from transgenic sickle cell mouse model

Sickle cell disease (SCD) is an autosomal recessive genetic red cell disorder characterized by the production of a defective form of hemoglobin, hemoglobin-S, that is worldwide-distributed. The acute clinical manifestations of SCD are related to hemoglobin cyclic-polymerization and to the generation of rigid, dense red blood cells (RBCs). We studied RBCs membrane proteome from human sickle RBCs, fractioned according to density compared to normal RBCs. 2-DE followed by MS analysis was carried out. We identified 65 proteins differently expressed, divided into five major clusters according to their functions: (i) membrane-cytoskeleton proteins; (ii) metabolic enzymes; (iii) ubiquitin-proteasome-system; (iv) flotillins; (v) chaperones. HSP27, HSP70 and peroxiredoxin-II (Prx-II) showed the most relevant changes. They were differently recruited to sickle RBCs membrane in response to in vitro hypoxia. Potential markers were then validated in a transgenic-mouse model for SCD, the SAD mice, exposed to hypoxia mimicking acute SCD vaso-occlusive-crisis (VOCs); we found that HSP70 and HSP27 bound to RBCs membrane respectively after 12?h and 48?h of hypoxia, while Prx-II membrane binding was modulated during hypoxia. Our data indicate that HSP27 and HSP70 play a novel role as RBCs membrane protein protectors and as possibly new markers of severity of RBCs membrane damage during acute VOCs.     

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.     

Label-free continuous lateral magneto-dielectrophoretic microseparators for highly efficient enrichment of circulating nucleated cells from peripheral blood

We have developed a continuous lateral magneto-dielectrophoretic (MAP-DEP) microseparator for the highly efficient enrichment of circulating nucleated cells from peripheral blood, based on native magnetic and dielectric properties of blood cells. Lateral magnetophoretic (MAP) force is achieved using a high-gradient magnetic field, caused by a ferromagnetic wire array inlaid on the bottom glass substrate. Lateral dielectrophoretic (DEP) force is achieved using a planar interdigitated electrode array, patterned on the top glass substrate. Red blood cells in peripheral blood are primarily driven by the lateral MAP force, while white blood cells are primarily forced by the lateral DEP force, the direction of which is opposite to that of the lateral MAP force. These lateral MAP and DEP forces are produced evenly on the whole area of the microchannel, thereby achieving highly efficient enrichment. The experimental results showed that the lateral MAP-DEP microseparator can continuously enrich circulating nucleated cells by 20,000-fold from peripheral blood simply by using an external magnetic flux of 0.3 T and a 2-MHz sinusoidal voltage of 4 Vp-p. Additionally, by using the intrinsic magnetic and dielectric properties of blood cells, we eliminated the need for laborious sample preparation procedures before and after enrichment, and also reduced the cost.     

A numerical study of an electrothermal vortex enhanced micromixer

Temperature gradients aroused from the Joule heating in a non-uniform electrical field can induce inhomogeneities of electric conductivity and permittivity of the electrolyte, thus causing an electrothermal force that generates flow motion. A 2D numerical investigation of a micromixer, utilizing electrothermal effect to enhance its mixing efficiency, is proposed in this paper. Results for temperature and velocity distributions, as well as sample concentration distribution are obtained for an electrolyte solution in a microchannel with different pairs of electrodes under AC potentials with various frequencies. Numerical solutions were first carried out for one pair of electrodes, with a length of 10 μm separated by a gap of 10 μm, on one side wall of a microchannel having a length of 200 μm and a height of 50 μm. It is found that the electrothermal flow effect, in the frequency range for which Coulomb force is predominant, induces vortex motion near the electrodes, thus stirring the flow streams and enhancing its mixing efficiency. If more than one pair of electrodes is located on the opposite walls of the microchannel, the mixing efficiency depends on the AC potential applied pattern and the electrodes arrangement pattern. The distance between two pairs of electrodes on two opposite walls is then optimized numerically. Sample mixing efficiencies, using KCl solutions as the working fluid in microchannels with different number of electrodes pairs at optimal electrodes arrangement pattern, are also investigated. If root mean squared voltages of 10 V in an AC frequency range of 0.1–10 MHz are imposed on 16 pairs of electrodes separated at an optimal distance, the numerical results show that a mixing efficiency of 98% can be achieved at the end of the microchannel having a length of 700 μm and a height of 50 μm at Re = 0.01 Pe _C = 100, and Pe _T = 0.07. However, the mixing efficiency decreases sharply at a frequency higher than 10 MHz owing to the drastically decrease in the Coulomb force.     

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.     

Effect of reservoir geometry on vortex trapping of cancer cells

Vortex-aided particle separation is a powerful method to efficiently isolate circulating tumor cells from blood, since it allows high throughput and continuous sample separation, with no need for time-consuming sample preprocessing. With this approach, only the larger particles from a heterogeneous sample will be stably trapped in reservoirs that expand from a straight microfluidic channel, allowing for efficient particle sorting along with simultaneous concentration. A possible limitation is related to the loss of particles from vortex traps due to particle–particle interactions that limit the final cellularity of the enriched solution. It is fundamental to minimize this issue considering that a scant number of target cells are diluted in highly cellular blood. In this work, we present a device for size-based particle separation, which exploits the well-consolidated vortex-aided sorting, but new reservoir layouts are presented and investigated in order to increase the trapping efficiency of the chip. Through simulations and experimental validations, we have been able to optimize the device design to increase the maximum number of particles that can be stably trapped in each reservoir and therefore the total efficiency of the chip.     

一种多功能正弦信号发生器的设计

介绍了一种以FPGA和单片机为控制核心,基于调制原理配合使用DDS专用芯片AD9851,实现了一种多功能正弦信号发生器。实现了在30Hz～12MHz频率范围内正弦信号的无失真输出,且在输出端接50Ω功率电阻的条件下,输出电压峰峰值在5.8V～6V范围内。系统还具有AM、FM、ASK、FSK、PSK调制的功能,整体工作稳定,界面友好,操作简单。     

基于FPGA的DDS信号源设计与实现

DDS广泛应用于电信与电子仪器领域,是实现设备全数字化的关键技术。文章设计并运用ISE10．0软件完成了三相正弦波信号、矩形波信号、调频调相信号的波形仿真,并以Xilinx的FPGA核心板SPARTAN3AN,结合高性能的MCU-ATMEGA128,完成了DDS的硬件设计及实现。仿真和实测结果表明,对于频率范围在0．1Hz到10MHz的正弦信号,输出信号的频率精度优于0．1％,频率稳定度优于10^-6,输出信号峰峰值≥20V,且相位以1°任意步进,具有电路简单、输出波形调整灵活以及性价比高等特点。     

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.     

Measurement of local electric field in microdevices for low-voltage electroporation of adherent cells

In this study, we present the measurement of the local electric field in a microdevice designed for electroporation of adherent cells. The microdevice mainly consists of a coverslip that has a transparent conductive layer and an insulating layer. The insulating layer has small cylindrical holes that focus the field lines to reduce the voltage required for electroporation. We estimated the local electric field at the cells by analyzing the ionic current based on a simple equivalent circuit model and investigated the correlation between the field strength and the efficiency of electroporation. We prepared various designs with matrices of electrodes with diameters ranging from 5 to 10 μm and center-to-center distances between adjacent electrodes ranging from 20 to 75 μm to perform systematic and statistical investigations. Furthermore, we discussed the efficiency of the electrode design in terms of the degree of field focusing, the applicability of optical observations, and the probability of positioning cells on the electrodes.     

Simultaneous electrokinetic flow and dielectrophoretic trapping using perpendicular static and dynamic electric fields

Microfluidics is a rapidly growing field that offers great potential for many biological and analytical applications. There are important advantages that miniaturization has to offer, such as portability, shorter response times, higher resolution and sensitivity. There is growing interest on the development of microscale techniques. Among these, electrokinetic phenomena have gained significant importance due to their flexibility for handling bioparticles. Dielectrophoresis (DEP), the manipulation of particles in non-uniform electric fields due to polarization effects, has become one of leading electrokinetic techniques. DEP has been successfully employed to manipulate proteins, DNA and a wide array of cells, form bacteria to cancer. Contactless DEP (cDEP) is a novel dielectrophoretic mode with attractive characteristics. In cDEP, non-uniform electric fields are created using insulating structures and external electrodes that are separated from the sample by a thin insulating barrier. This prevents bioparticle damage and makes cDEP a technique of choice for many biomedical applications. In this study, a combination of cDEP generated with AC potentials and electrokinetic liquid pumping generated with DC potentials is employed to achieve highly controlled particle trapping and manipulation. This allows for lower applied potentials than those used in traditional insulator-based DEP and requires a simpler sytem that does not employ an external pump. This is the first demonstration of electrokinetic (EK) pumping in which the driving electrodes are not in direct contact with the sample fluid. Multiphysics simulations were used to aid with the design of the system and predict the regions of particle trapping. Results show the advantages of combining AC-cDEP with DC EK liquid pumping for dynamic microparticle trapping, release and enrichment.     

Droplet group production in an AC electro-flow-focusing microdevice

We report the production of droplet groups with a controlled number of drops in a microfluidic electro-flow-focusing device under the action of an AC electric field. This regime appears for moderate voltages (500–700 V peak-to-peak) and signal frequencies between 25 and 100 Hz, much smaller than the droplet production rate (\({\sim }\,{500}\) Hz). For this experimental condition the production frequency of a droplet package is twice the signal frequency. Since the continuous phase flow in the microchannel is a Hagen–Poiseuille flow, the smaller droplets of a group move faster than the bigger ones leading to droplet clustering downstream.     

Controlling reflectivity of silver-corundum-silver nanostructure by DC voltage

Significant changes of the permittivity of a silver film have been detected using the surface plasmon resonance (SPR) method when a constant electric field is applied to the 177-nm dielectric corundum film placed between two silver films 49 nm and 36 nm thick. The effect manifests itself as a significant change of the reflectivity of the structure when the voltage of up to 30 V is applied to the electrodes. It is shown that the optical parameters of the anode and cathode layers strongly differ if dc voltage is above 4 V.     

源搅拌混响室天线布置方式实验研究

根据谐振腔理论,分析了理想情况下影响源搅拌混响室性能的主要因素.通过实验方法,对提出的两种源搅拌方案从场均匀性和统计特性两方面进行分析.经过对采样数据处理可知,在一定数量采样值的情况下,这两种方式都可以实现较好的场均匀性,同时借助K-S拟合对测量值的统计特性进行了分析,结果表明源搅拌混响室的一维场分布服从瑞利分布,通过...