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The dielectrophoresis (DEP) interactions of a few particles in a uniform two-dimensional (2D) electrical field have well been studied by Maxwell stress tensor (MST) method. Multiple particle interactions in three-dimensional (3D) electrical field are investigated in this work using iterative dipole moment (IDM) method which is an analytic algorithm without complicated numerical computations to solve for electrical field. The interactive DEP forces of particles calculated by IDM are found to be well agreed with those of MST method and much simple to implement. Using IDM method, a series of examples of multiple particles interactions and particle chains in a 3D uniform DC electrical field is presented. Randomly distributed similar dense particles (either all positive DEP (pDEP) or all negative DEP (nDEP) particles) in 3D uniform electrical field can generally form chains in lines parallel to the electrical field, except the case that all similar particles are in a plane perpendicular to the electrical field where the particles repel each other and move away in the plane. Randomly distributed dissimilar dense particles (mixture of pDEP and nDEP particles) can form (1) chains in lines, (2) clusters in a plane or (3) 3D groups. The chains, clusters and groups are of staggered arrangements of pDEP and nDEP particles, which are perpendicular to the electrical field.

In this paper, an integrated microfluidic analysis microsystems with bacterial capture enrichment and in-situ impedance detection was purposed based on microfluidic chips dielectrophoresis technique and electrochemical impedance detection principle. The microsystems include microfluidic chip, main control module, and drive and control module, and signal detection and processing modulet and result display unit. The main control module produce the work sequence of impedance detection system parts and achieve data communication functions, the drive and control circuit generate AC signal which amplitude and frequency adjustable, and it was applied on the foodborne pathogens impedance analysis microsystems to realize the capture enrichment and impedance detection. The signal detection and processing circuit translate the current signal into impendence of bacteria, and transfer to computer, the last detection result is displayed on the computer. The experiment sample was prepared by adding Escherichia coli standard sample into chicken sample solution, and the samples were tested on the dielectrophoresis chip capture enrichment and in-situ impedance detection microsystems with micro-array electrode microfluidic chips. The experiments show that the Escherichia coli detection limit of microsystems is $5\times 10^4$ CFU/mL and the detection time is within 6 min in the optimization of voltage detection 10 V and detection frequency 500 KHz operating conditions. The integrated microfluidic analysis microsystems laid the solid foundation for rapid real-time in-situ detection of bacteria.

The design of a MEMS ultrasonic sensor has been presented that exploits the Single Bubble Sonoluminescence (SBSL) phenomenon to realize an energy transduction mechanism from acoustical to electrical domain. In the developed scheme, highly stable laser like short duration light pulses are emitted when ultrasound waves strike a thermally generated microbubble stabilized in a confined volume of 1% xenon-enriched water. The emitted light pulses are detected by an integrated profiled silicon type photodetector to generate ultrastable 100 picoseconds duration current pulses per acoustical cycle. The sensor exhibits energy amplification during the transduction process itself that is not achievable by conventional types of MEMS or non-MEMS acoustical sensors. The cylindrical sensor geometry is 650 μm in diameter and 300 μm in height and is designed to have a sensitivity of 5.56 mA/atm/cycle. The sensor can be used in applications where detection of high pressure ultrasound waves is necessary or as an ultrastable very short duration current pulse generator for use in tissue and nerve repair or microsurgery.

This paper presents a novel dielectrophoresis (DEP) device where the DEP electrodes define the channel walls. This is achieved by fabricating microfluidic channel walls from highly doped silicon so that they can also function as DEP electrodes. Compared with planar electrodes, this device increases the exhibited dielectrophoretic force on the particle, therefore decreases the applied potential and reduces the heating of the solution. A DEP device with triangle electrodes has been designed and fabricated. Compared with the other two configurations, semi-circular and square, triangle electrode presents an increased force, which can decrease the applied voltage and reduce the Joule effect. Yeast cells have been used to for testing the performance of the device.

The assembly of multiwalled carbon nanotube (MWCNT) films through dielectrophoresis is described and the electrical response of aligned and randomly oriented MWCNT films to temperature variations is evaluated. The resistance of the randomly oriented MWCNT films was found to decrease exponentially with temperature. The decrease was less marked when the films were annealed and kept dehydrated during the electrical measurements. Alignment of MWCNTs led to an apparent reduction in the electrical response of the films with temperature changes and a small measurement-to-measurement variability, suggesting that dielectrophoresis-aligned MWCNT films would be more reproducible detectors in applications exploiting CNT-mediated electronic sensing.

Dielectrophoresis (DEP) force is generated by dielectrically polarized particles in non-uniform electrical fields. In this paper, we report the use of DEP in microfluidic sample preparation. The chip uses DEP force to concentrate mammal cells and magnetic beads, in order to extract and purify mRNA from these cells. Both the mammal cells and magnetic beads exhibit negative DEP properties and are concentrated in the same region in the electrical field ie. regions of weaker electrical field of the chip. Therefore, the magnetic beads coated with Oligo (dT) can easily capture mRNA released from the cells when cell is lysed by chemical lyse. Thus a high mRNA yield can be obtained. Silicon is used to make the chip channel and the DEP electrodes. The working principle of the micro-fluidic chip, its fabrication process and experiment results are described in this report.

Cell-based approaches in medicine, biotechnology and in pharmaceutical research offer unique prospects to cope with future challenges in the field of public health. Stem cell research, autologous cell therapies and tissue engineering are only a few possible key applications. Progress in these fields will depend on the successful implementation of versatile and flexible tools for the gentle manipulation and characterization of cells. In recent years, we and others have introduced microfluidic lab-on-chip systems that include dielectrophoretic elements for the contact-less handling and the analysis of cells. Here, we present results that were obtained by combining our labon-on-chip devices with a low-cost centrifugation stage for the efficient and gentle separation of microparticles and live human cells. Our approach is supposed to overcome limitations that arise from the use of bulky and expensive external pumping stages.

The performance of a nanoscale sensor is not limited by the sensitivity of the sensor itself but rather by the diffusion time required for target molecules to reach to the extremely small sensor surface. In this work, we developed a carbon nanotube device that performed the dual functions of concentrating and detecting microorganisms in a sample solution. The sensor surface area was increased by fabricating a carbon nanotube network device using thermal chemical vapor deposition and standard microfabrication techniques. The target Escherichia coli (E. coli) cells were concentrated at the sensor surface via dielectrophoretic concentration by the carbon nanotube network channels. After 10 min of collection, the chip was washed with ample amounts of a clean buffer solution, and only the E. coli cells that were bound to the antibodies remained on the sensor surface. The binding of E. coli to the CNT network device decreased the conductance, presumably due to an increase in the scattering at the sensor surface. The detection limit and the time required for microorganism detection was greatly improved by combining dielectrophoresis with the carbon nanotube devices.

"Label-free" biomolecule sensors are designed and fabricated utilizing polystyrene microparticles and gold nanoparticles as sensing elements for quantification of the ultrasensitive cardiac biomarker troponin-T. A powerful diagnostic tool electrochemical impedance spectroscopy, used to characterize significant changes at biomolecular level, has been employed to detect troponin-T at 10 fg/mL sensitivity in phosphate buffered saline. This paper presents the theory, modeling and experimental study on the behavior of micro and nanoparticles under the influence of applied sinusoidal potential. This paper also demonstrates the advantages of utilizing gold nanoparticles to amplify electrical impedance signals obtained due to particle–biomolecule conjugation for designing electrical immunoassays for detecting troponin-T. The results indicate that electrode design and particle scaling are critical factors that determine the performance for rapid biomolecular analysis. Size-based scaling enhances sensitivity by amplifying the measured signal by an order of 10 when the sizes of the particles were reduced from 5 μm to 5 nm.

In this paper, a dielectrophoretic (DEP) micro separator is studied for plasma-blood separation. DEP forces created by non-uniform electric fields are used as deflected forces to deplete blood cells from side walls at a given inlet flow rate (Q_in). Then one can extract plasma through a microchannel on side wall at certain extraction flow rate (Q_p). In this experiment, saline isotonic solution is chosen as dilute solution for whole blood. The minimum dilute ratio (whole blood: saline dilute) is found to be 1:3 for DEP to substantially deplete blood cells from side walls. Exraction of plasma from whole blood sample by DEP force is also investigated. Experimental results show blood cells do not enter side channel by DEP force at inlet flow rate Q_in=0.5 μ1/min when plasma extract flow rates is Q_p ≤ 0.3 μ1/min. By calculating pure plasma extraction volume fraction, the efficiency in current experiment can reach as high as 20% if dilute ratio 1:3 of whole blood sample is considered.

This article reports a new class of silicon-based microgas sensors utilizing hexagonally-ordered mesoporous carbon powders (MCPs) as the sensitive film. The mesoporous carbon powders featuring high-specific surface area are replicated by the SBA-15 silica template and immobilized between Cr electrodes on a 9 × 9 cm silicon chip by using a.c. dielectrophoresis (DEP) process at room temperature. The silicon sensor platform comprises Cr microheaters embedded in a dielectric thin membrane manufactured by microelectromechanical systems back-etching techniques. It is shown that MCPs can be satisfactorily aligned along electric fields and accumulated to the electrode area. Investigations into CO detection are carried out to verify gas-sensitive characteristics of the MCP nanofilm. Our experimental results disclose the mesoporous carbon powders are successfully chemoresistive to CO, and demonstrate distinct resistance change with respect to ppm-level variation. In addition, response time, recovery time, and reproducible sensing behavior are experimentally obtained.

A microelectrode array-based cell electrofusion chip was fabricated by using the MEMS technique. Because of the short distance between two counter microelectrodes, the working voltage on this chip was only 1/100–1/20 as that in the traditional cell electrofusion method. Simulation method was used to analyze the on-chip electric field distribution and optimize the structure of the microelectrodes. The results showed the length and width of the microelectrode, and the distance between two microelectrodes in the horizontal and vertical direction would impact the strength and distribution of the electric field. Thus, optimized chip architecture was obtained, on which six individual chambers were integrated. At least 1680 microelectrodes were patterned within any one chamber. Alternating current signals have been used to manipulate and align cells, and most cells were aligned as cell–cell twins. High-intensity (~10³ V/cm) electric pulses were used to fuse the aligned cell–cell twins. The fusion efficiency was about 40%, which was much higher than that in traditional chemical method (less than 1‰) and electrofusion methods (less than 5%).

This paper presents the simulation of general and travelling dielectrophoretic forces, as well as the movement of the particles in a sandwich structure micro-device. The electrode geometry of the micro device used for simulation is an interdigitated bar electrode. The simulation method used to solve the equations is based on the least square finite difference method (LSFD). The simulation first calculates all forces acting at any place in the chamber, with these forces the trajectory of a particle can now be proposed. All of the particles parameters like radius, voltage, initial height, etc can easily be changed and the simulation can be redone. With this continuous trial we receive different behavior of the particles and examine the relevancy of the different changes made. This detailed information about the influences of the parameters on the procedure in the micro-device can be used for the development of further micro-devices.