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.     

On-chip separation of Lactobacillus bacteria from yeasts using dielectrophoresis

Dielectrophoresis, the induced motion of dielectric particles in non-uniform electric fields, enables the separation of suspended bio-particles based on their dimensions or dielectric properties. This work presents a microfluidic system, which utilises a combination of dielectrophoretic (DEP) and hydrodynamic drag forces to separate Lactobacillus bacteria from a background of yeasts. The performance of the system is demonstrated at two operating frequencies of 10?MHz and 100?kHz. At 10?MHz, we are able to trap the yeasts and bacteria at different locations of the microelectrodes as they experience different magnitudes of DEP force. Alternatively, at 100?kHz we are able to trap the bacteria along the microelectrodes, while repelling the yeasts from the microelectrodes and washing them away by the drag force. These separation mechanisms might be applicable to automated lab-on-a-chip systems for the rapid and label-free separation of target bio-particles.     

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.

     

Particle separation in alternating-current electro-osmotic micropumps using field-flow fractionation

This work presents a novel method for continuous particle separation on the microscale by means of field-flow fractionation. It is based on the use of asymmetric interdigitated electrode arrays on the channel bottom, which induce an electro-osmotic channel flow when driven harmonically. Suspended particles are influenced by viscous fluid drag, sedimentation as well as by dielectrophoretic repulsion forces from the driving electrodes due to the emerging electric field. The significant dependance of the present forces on particle properties allows for separation with respect to particle density and size. This work analyzes electric and flow field by means of the finite element method and investigates the size and density dependent particle motion as a function of driving voltage and frequency of the electrode array. Matching these driving parameters permits the separation of sedimenting particles by their density independently from their size as well as the separation by size. Finally, channel designs are proposed which enable standard separation by means of selective particle mobility in the channel, separation in terms of opposing motion directions, as well as continuous lateral separation.     

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.     

Robust properties of periodic discrete and multirate systems

For discrete periodic and multirate systems new bounds are derived for three different robustness problems: disturbance attenuation, and stability with time-varying structured and unstructured parameter variations. These results generalize the single rate results to allow multirate capability     

Low-cost microelectrode array with integrated heater for extracellular recording of cardiomyocyte cultures using commercial flexible printed circuit technology

This article reports the use of commercial, flexible printed circuit technology for the fabrication of low-cost microelectrode arrays (MEAs) for recording extracellular electrical signals from cardiomyocyte cultures. A 36-electrode array has been designed and manufactured using standard, two-layer, polyimide-based flexible circuit technology, with electrode diameters of 75 and 100 μm. Copper structures defined on the backside of the array have been used for low-power thermal regulation of the culture. Electrical characterization of the gold-plated electrodes showed impedances below 250 kΩ at 1 kHz. Functional testing was conducted using HL-1 cardiac myocytes. The arrays proved biocompatible, and supported the formation of functional syncytia, as demonstrated by electrical recordings of depolarization waves across the array. A comparison with conventional, glass-based MEAs is presented, which reveals differences in signal strength (smaller for larger electrode) and variability (less for larger electrodes), but no effect of the substrate types on culture parameters such as beat rate or conduction velocity. The performance of the on-chip heating was evaluated, with typical temperature settling times (to ±0.1 °C) below 10 s, for a power consumption around 1 W (at 37 °C). Accuracy and stability are discussed. HL-1 cell responses to various temperature profiles enabled by the on-chip heating are presented, showing a remarkable correlation between temperature and beat rate.     

线性离散周期奇异系统的可解性与渐近稳定性

讨论了线性离散周期奇异系统初值问题的可解性和渐近稳定性问题.首先分析总结了线性离散变系数奇异系统可解性及其广义状态解的一般概念.在此基础上,定义了线性离散变系数奇异系统的一致渐近稳定性,并通过增加系统维数把线性离散周期奇异系统转化为线性定常奇异系统,从而得到了线性离散周期奇异系统可解和一致渐近稳定的充要条件.     

Design and fabrication of a microelectrode array for iodate quantification in small sample volumes

A method for the simple manufacture of microelectrode arrays is described. The construction technique is based on microelectronics technology by conventional sputtering deposition of layers of Ni/Cr and Au, photolithography and a final treatment to improve the chemical stability of the device. Cyclic voltammetry at both sulphuric acid and ferricyanide solutions was employed to inspect the operation of the microelectrodes, which can be individually addressable. This microelectrode system has been used successfully for indirect amperometric measurements of the iodate content in very small volumes (typically 50–200 μL) of solutions prepared from the dissolution of commercial Brazilian salt samples, which illustrates its potentiality as useful tools in electroanalytical chemistry. The possibility of modifying the surface of the gold microelectrodes by electrodeposition of molybdenum oxides was also investigated. The results indicated that the device can also be used as a practical sensor for measuring directly iodate owing to the enhancement of the reduction signal by an electrocatalytic process.     

Existence and uniqueness results for discrete second-order periodic boundary value problems

We prove existence and uniqueness results for solutions of second-order nonlinear difference equations on a finite discrete segment with periodic boundary conditions. The results are based on the notion of upper and lower solutions.     

Design of multiobjective reconfigurable antenna array with discrete phase shifters using multiobjective differential evolution based on decomposition

The reconfigurable design problem is to find the element that will result in a sector pattern main beam with side lobes. The same excitation amplitudes applied to the array with zero phase should be in a high directivity, low‐side lobe pencil‐shaped main beam. This work presents a multiobjective approach to solve this problem. We consider two design objectives: the minimum value for the dual beam and the dynamic range ratio in qualify the entire array radiation pattern in order to achieve the optimal value between the antenna‐array elements. We use a recently developed and very competitive multiobjective evolutionary algorithm, called MOEA/D. This algorithm uses a decomposition approach to convert the problem of approximation of the Pareto Front into a number of single objective optimization problems. We illustrate that the best solutions obtained by the MOEA/D can outperform stat‐of‐art single objective algorithm: generalized generation‐gap model genetic algorithm (G3‐GA) and differential evolution algorithm (DE). In addition, we compare the results obtained by MOEA/D with those obtained by one of the most widely multiobjective algorithm called NSGA‐II and mutliobjective DE. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 675–681, 2012.     

Improvement of microchannel geometry subject to electrokinesis and dielectrophoresis using numerical simulations

This paper addresses the effects of microchannel geometry with electrically insulating posts on a particle flow driven by electrokinesis and dielectrophoresis. An in-house numerical program is developed using a numerical model proposed in literature to predict particle flows in a microchannel with a circular post array. The numerical program is validated by comparing the results of the present study to those in the literature. Results obtained from a Monte-Carlo simulation confirm the three particle flow types driven by an external DC electric field: electrokinetic flow, streaming dielectrophoretic flow, and trapping dielectrophoretic flow. In addition, we study the effects of electrokinetic and dielectrophoretic forces on particle transports by introducing a ratio of lateral to longitudinal forces exerted on a particle. As a result, we propose an improved microchannel geometry to enhance particle transports across electrokinetic streamlines for a given power dissipation. The improved microchannel has a shorter longitudinal spacing between the circular posts than a reference microchannel. We also discuss the critical values of dimensionless variables that distinguish the three particle flow types for both improved and reference microchannels.     

Limitations of nonlinear discrete periodic control for disturbance attenuation and robust stabilization

This paper presents a performance analysis of nonlinear periodically time-varying discrete controllers acting upon a linear time-invariant discrete plant. Time-invariant controllers are distinguished from strictly periodically time-varying controllers. For a given nonlinear periodic controller, a time-invariant controller is constructed. Necessary and sufficient conditions are given under which the time-invariant controller gives strictly better control performance than the time-invariant controller from which it was obtained, for the attenuation of l_p exogenous disturbances and the robust stabilization of l_p unstructured perturbations, for all p[1,∞].     

Particle separation and sorting in microfluidic devices: a review

Separation and sorting of micron-sized particles has great importance in diagnostics, chemical and biological analyses, food and chemical processing and environmental assessment. By employing the unique characteristics of microscale flow phenomena, various techniques have been established for fast and accurate separation and sorting of microparticles in a continuous manner. The advancements in microfluidics enable sorting technologies that combine the benefits of continuous operation with small-sized scale suitable for manipulation and probing of individual particles or cells. Microfluidic sorting platforms require smaller sample volume, which has several benefits in terms of reduced cost of reagents, analysis time and less invasiveness to patients for sample extraction. Additionally, smaller size of device together with lower fabrication cost allows massive parallelization, which makes high-throughput sorting possible. Both passive and active separation and sorting techniques have been reported in literature. Passive techniques utilize the interaction between particles, flow field and the channel structure and do not require external fields. On the other hand, active techniques make use of external fields in various forms but offer better performance. This paper provides an extensive review of various passive and active separation techniques including basic theories and experimental details. The working principles are explained in detail, and performances of the devices are discussed.     

Priority-based Media Delivery using SVC with RTP and HTTP streaming

Media delivery, especially video delivery over mobile channels may be affected by transmission bitrate variations or temporary link interruptions caused by changes in the channel conditions or the wireless interface. In this paper, we present the use of Priority-based Media Delivery (PMD) for Scalable Video Coding (SVC) to overcome link interruptions and channel bitrate reductions in mobile networks by performing a transmission scheduling algorithm that prioritizes media data according to its importance. The proposed approach comprises a priority-based media pre-buffer to overcome periods under reduced connectivity. The PMD algorithm aims to use the same transmission bitrate and overall buffer size as the traditional streaming approach, yet is more likely to overcome interruptions and reduced bitrate periods. PMD achieves longer continuous playback than the traditional approach, avoiding disruptions in the video playout and therefore improving the video playback quality. We analyze the use of SVC with PMD in the traditional RTP streaming and in the adaptive HTTP streaming context. We show benefits of using SVC in terms of received quality during interruption and re-buffering time, i.e. the time required to fill a desired pre-buffer at the receiver. We present a quality optimization approach for PMD and show results for different interruption/bitrate-reduction scenarios.     

Multi-instance classification through spherical separation and VNS

A two-class classification problem is considered where the objects to be classified are bags of instances in d-space. The classification rule is defined in terms of an open d-ball. A bag is labeled positive if it meets the ball and labeled negative otherwise. Determining the center and radius of the ball is modeled as a SVM-like margin optimization problem. Necessary optimality conditions are derived leading to a polynomial algorithm in fixed dimension. A VNS type heuristic is developed and experimentally tested. The methodology is extended to classification by several balls and to more than two classes.     

Analytical formulation of electric field and dielectrophoretic force for moving dielectrophoresis using Fourier series

Electrokinetics manipulation and separation of living cells employing microfluidic devices require good knowledge of the strength and distribution of electric field in such devices. AC dielectrophoresis is performed by generating non-uniform electric field using microsize electrodes. Among the several applications of dielectrophoretic phenomenon, this present study considers the recently introduced phenomenon of moving dielectrophoresis. An analytical solution using Fourier series is presented for the electric field distribution and dielectrophoretic force generated inside a microchannel. The potential at the upper part of the microchannel has been found by solving the governing equation of the electric potential with specific boundary conditions. The solutions for the electric field and dielectrophoretic force show excellent agreement with the numerical results. Microdevices were fabricated and experiments were carried out with living cells confirming and validating the analytical solutions.     

Fabrication of bio/nano interfaces between biological cells and carbon nanotubes using dielectrophoresis

The authors have previously demonstrated the manipulation of bacteria and carbon nanotubes (CNTs) using dielectrophoresis (DEP) and its application for various types of biological and chemical sensors. This paper demonstrates simultaneous DEP handling of bacteria and CNTs, which are mixed and suspended in water. The CNTs were solubilized in water using microplasma-based treatment. When a microelectrode was energized with an ac voltage in the suspension of Escherichia coli (E. coli) cells and multi-walled CNTs (MWCNTs), both of them were simultaneously trapped in the microelectrode gap. Scanning electron microscopy (SEM) images revealed that E. coli cells were trapped on the surface or the tip of MWCNTs, where the electric field strength was intensified due to high aspect ratio of MWCNTs. As a result, bio/nano interfaces between bacteria and MWCNTs were automatically formed in a self-assembly manner. A potential application of the DEP-fabricated bio/nano interfaces is a drug delivery system (DDS), which is realized by transporting drug molecules from CNTs to cells across the cell membrane, which can be electroporated by the local high electric field formed on the CNT surface.     

Video processing for panoramic streaming using HEVC and its scalable extensions

Multimedia Tools and Applications - Panoramic streaming is a particular way of video streaming where an arbitrary Region-of-Interest (RoI) is transmitted from a high-spatial resolution video, i.e....     

Flexible and efficient IR using array databases

The Matrix Framework is a recent proposal by Information Retrieval (IR) researchers to flexibly represent information retrieval models and concepts in a single multi-dimensional array framework. We provide computational support for exactly this framework with the array database system SRAM (Sparse Relational Array Mapping), that works on top of a DBMS. Information retrieval models can be specified in its comprehension-based array query language, in a way that directly corresponds to the underlying mathematical formulas. SRAM efficiently stores sparse arrays in (compressed) relational tables and translates and optimizes array queries into relational queries. In this work, we describe a number of array query optimization rules. To demonstrate their effect on text retrieval, we apply them in the TREC TeraByte track (TREC-TB) efficiency task, using the Okapi BM25 model as our example. It turns out that these optimization rules enable SRAM to automatically translate the BM25 array queries into the relational equivalent of inverted list processing including compression, score materialization and quantization, such as employed by custom-built IR systems. The use of the high-performance MonetDB/X100 relational backend, that provides transparent database compression, allows the system to achieve very fast response times with good precision and low resource usage.