Papers by Keyword: Dielectrophoresis

Abstract: Gold nanoparticles (AuNPs) is known for its high surface area to volume ratio which acts as an excellent receptor when placed in between electrodes in sensors application. Microelectrodes which are bar and needle shape pointed ends with two arrangements; comb and castle wall configurations were designed to be used for fabrication of electrodes to observe the relation between geometry of electrodes and dielectrophoretic of AuNPs on p-gallium nitride (GaN) substrates. The dielectrophoretic behaviour and electrical properties were analysed before and after the drop cast of AuNPs using current-voltage (I-V) curve method with manual probing. Resistance values of each sample were calculated under reverse bias condition. The effect of design on the nanomanipulation of AuNPs will be discussed.

Abstract: A major challenge in chemical engineering is the separation and purification of materials, especially of rare earth compounds. It has been reported that a dielectrophoretic (DEP) apparatus can be used for separating rare earth oxides. The DEP capture of REOs on screen electrode was observed with microscope. The concentration of ROEs was determined using a nephelometer and ICP-OES before and after injection into the DEP apparatus. The results show that three types of REOs, La₂O₃, CeO₂ and Dy₂O₃, generate nDEP in the DEP capture apparatus. There are two factors: voltage and suspension concentration, that affect the capture rate. The capture rate increases as voltage rises within certain limits. The capture rate also increases with increase in the original suspension concentration. Different REOs show marked differences in the DEP capture conditions. Consequently, factors such as voltage and flow rate can be controlled to achieve separation of different REOs.

Abstract: Dielectrophoresis (DEP) force will arise when an inhomogeneous AC electric field with sinusoidal wave is applied to microelectrodes. By using DEP, we could distinguish between viable and non-viable cells by their movement through a non-uniform electric field. In this paper, we propose a yeast cell separation system, which utilizes an Au DEP chip and an optical tweezers. The Au DEP chip is planar quadrupole microelectrodes, which were fabricated by Au thin-film and a box cutter. This fabrication method is low cost and simpler than previous existing methods. The tip of the optical tweezers was fabricated by dynamic chemical etching in a mixture of hydrogen fluoride and toluene. The optical tweezers has the feature of high manipulation performance. That does not require objective lens for focusing light because the tip of optical tweezers has conical shape. By using both the Au DEP chip and optical tweezers, we could obtain three-dimensional manipulation of specific cells after viability separation.

Abstract: Microelectrode geometry has significant influence on particles trapping techniques used on bioanalysis platforms. In this paper, the particle trapping patterns of dipole, quadrupole and octupole microelectrode using dielectrophoretic force (DEP) are discussed. The microelectrodes were constructed on a metal-insulator-metal platform, built on a silicon nitride (Si₃N₄) coated silicon substrate. The back contact is made from 20 nm nickel-chromium (NiCr) and 100 nm gold (Au) as the first layer. Then, SU-8-2005 (negative photoresist) is used on the second layer to create microcavities for trapping the particles. The third layer, where the three geometries were patterned, is made from 20 nm NiCr and 100 nm Au layers. Prior to fabrication, the particles trapping patterns of the microelectrodes were profiled using a finite element software, COMSOL 3.5a. Trapping patterns for the three geometries were evaluated using polystyrene latex microbeads. Results from the experiment validate simulation studies in term of microelectrode trapping ability up to single particle efficiency. It provides the potential of converting the trapping platform into a lab-on-chip system.

Abstract: In this paper, we proposed a four-electrode microdevice for precise isolating and trapping of a single cell using negative dielectrophoresis (nDEP) forces. To generate appropriate nDEP forces, sinusoidal alternating currents (AC) signals with various phase shifting were applied to the microelectrodes, and the finite element analysis (FEA) techniques were used to analyze the resulted electric field distribution. The simulation results implied that effective trapping and rotation forces can be realized by the proposed device structure under specific excitation condition. The geometry effect on the electric field distributions of electrodes was further studied in details. For the electrodes with 50 μm width, the maximum value of the gradient of the squared field strength could reach 10⁶ V²/m³, which is higher than that for electrodes with 20 μm width. The influences of applied voltage to electric field gradient were also simulated and the result shows that the dielectrophoresis (DEP) force increased significantly with the magnitude of applied voltage. These preliminary results may provide useful insight and design guidelines for the future DEP microstructure design and fabrication.

Abstract: Due to their excellent properties, carbon nanotubes (CNTs) have the potential to be applied as functional elements for nanoelectronics, nanoelectromechanical systems, new energy, sensors, and others. One precondition for many of these applications is to assemble CNTs into devices and the number and position of assembled CNTs usually need to be controlled. The process factors for CNT assembly by dielectrophoresis (DEP), which include the magnitude of the applied voltage, the concentration of the CNT suspension, the duration of the electric field, and the geometry of the CNTs, and the shape of the electrodes, have great influence on the assembly results. Some techniques based on DEP, such as those adding floating electrodes, optically induced DEP (ODEP) and using hydrodynamic force, can realize precise positioning of CNTs. This paper introduces the factors and techniques which influence the number and position of assembled CNTs. The research intends to provide help for the application of CNTs in nanoelectronics.

Abstract: Carbon nanotubes (CNTs) have been widely studied for their unique size-dependent electrical, mechanical, and chemical properties. However, CNTs need to be precisely positioned in complex device structures. Dielectrophoresis (DEP) is an effective and practical method for precise assembly of CNTs. In this paper, the researches on simulation of precise positioning of CNTs by DEP are reviewed. Single electrode pairs include those with round, triangle, and rectangular tip shapes and electrode arrays such as comb electrodes are also taken accounted. The moving trajectories of CNTs during DEP from the selected literature are introduced. The effect of floating electrodes on precise manipulation of CNTs is examined as well.

Abstract: We propose fabrication method of a planar quadrupole microelectrode for dielectrophoresis (DEP), which is fabricated by Au thin-film, ion coater and box cutter. This method is more cost effective and simpler than previous existing methods. We conducted two experiments for confirming usefulness of the Au DEP chip. Those are separation of yeast cells and trap force of DEP. To separate yeast cells, we used viable and non-viable cells. DEP force arises when an inhomogeneous AC electric field and sine wave frequency were applied to microelectrode. The Au DEP chip is able to distinguish between viable and non-viable cells and separate them by frequency dependence and the flow with Syringe pump. The chip can obtain viable cells which were trapped without contact to the microelectrode. The viable cells can use for fusion or cell culture. Furthermore, we carried out another experiment to investigate the trap force. The trap force of Negative-DEP becomes gradually weak when the frequency increases with 0.1, 0.5 and 1MHz. We were able to confirm relation between trap force and frequency by the Au DEP chip. The trap force has frequency dependence. Through the two experiments, we have established usefulness of the Au DEP chip.

Abstract: Cell fusionis difficult so that research institutions try to fusion with many methods. For example, method of using polyethylene glycol (PEG) is useful and it mainly use in fusion. However cell fusion efficiency of this method is less. In this paper we suggest efficient fusion of PEG with combining optical tweezers and dielectrophoresis (DEP). Optical tweezers is useful tool in cell manipulation ant it has features of non-invasive and non-contact. Using this technique, we can take target cell from many cells. DEP are known to manipulate cell and form pearl chain by non-uniform electric field. We think DEP lead to efficient cell fusion of PEG because probability of cell adhered by only PEG is less.So we performed firstly take protoplast of red cabbage as specific cell from cells to parallel electrodes by optical tweezers and second, we observed cell-cell fusion by PEG with cell formed pearl chain by DEP. Furthermore we demonstrated using optical tweezers at 980 nm, showed manipulation dates of polymer microspheres, yeast cell and protoplast of red cabbage.

Abstract: Generally, the metal probe for NSOM (Near field scanning optical microscopy) or STM (Scanning Tunneling Microscope) was made with gold or tungsten. However, they were not suitable for the cell trap in our research for the reasons of cost, hardness, etc. In our research, these problems were solved by choosing brass as a material of a probe. Since the probe production by electrolytic polishing can change the shape of the top, tip angle, and taper length etc, we can propose a probe suitable for a cell trap. Therefore, in this examination, we propose the brass probe by electrolytic polishing with low cost and sufficient hardness for cell trap.