Showing papers by "Gwo-Bin Lee published in 2004"

Vertical focusing device utilizing dielectrophoretic force and its application on microflow cytometer

Abstract: Focusing of particles/cells in the vertical direction inside a micromachined flow cytometer is a critical issue while using an embedded optical detection system aligned with microchannels. Even if the particles/cells have been focused centrally in the horizontal direction using coplanar sheath flows, appreciable errors may still arise if they are randomly distributed in the vertical direction. This work presents a vertical focusing device utilizing dielectrophoretic (DEP) forces and its application on micromachined flow cytometer. A pair of parallel microelectrodes is deposited on the upper and bottom surface of the microfluidic channel to drive particles/cells into the vertical center of the sample flow. This new microfluidic device is capable of three-dimensional (3-D) focusing of microparticles/cells and thus improves the uniformity of the optical detection signals. This 3-D focusing feature of the sample flow is realized utilizing the combination of dielectrophoretic and hydrodynamic forces. Initially, two sheath flows are used to focus the sample flow horizontally by means of hydrodynamic forces, and then two embedded planar electrodes apply negative DEP forces to focus the particles/cells vertically. A new micromachined flow cytometer integrated with an embedded optical detection mechanism is then demonstrated. Numerical simulation is used to analyze the operation conditions and the dimension of the microelectrodes for DEP manipulation. The dynamic trace of the moving particles/cells within a flow stream under the DEP manipulation is calculated numerically. Micro polystyrene beads and diluted human red blood cells (RBC) are used to test the performance of the proposed device. The experimental results confirm the suitability of the proposed device for applications requiring precise counting of particles or cells. Experimental data indicates the proposed method can provide more stable signals over the other types of micromachined flow cytometers that were previously reported.

Electrokinetically driven active micro-mixers utilizing zeta potential variation induced by field effect

Abstract: This paper presents a new electrokinetically driven active micro-mixer which uses localized capacitance effects to induce zeta potential variations along the surface of silica-based microchannels. The mixer is fabricated by etching bulk flow and shielding electrode channels into glass substrates and then depositing Au/Cr thin films within the latter to form capacitor electrodes, which establish localized zeta potential variations near the electrical double layer (EDL) region of the electroosmotic flow (EOF) within the microchannels. The potential variations induce flow velocity changes within a homogeneous fluid and a rapid mixing effect if an alternating electric field is provided. The current experimental data confirm that the fluid velocity can be actively controlled by using the capacitance effect of the buried shielding electrodes to vary the zeta potential along the channel walls. While compared with commonly used planar electrodes across the microchannels, the buried shielding electrodes prevent current leakage caused by bad bonding and allow direct optical observation during operation. It also shows that the buried shielding electrodes can significantly induce the field effect, resulting in higher variations of zeta potential. Computational fluid dynamic simulations are also used to study the fluid characteristics of the developed active mixers. The numerical and experimental results demonstrate that the developed microfluidic device permits a high degree of control over the fluid flow and an efficient mixing effect. Moreover, the developed device could be used as a pumping device as well. The development of the active electrokinetically driven micro-mixer could be crucial for micro-total-analysis-systems.

Minimal dead-volume connectors for microfluidics using PDMS casting techniques

Abstract: This paper presents a minimal dead-volume micro-connector fabricated using poly-dimethylsiloxane (PDMS) casting techniques for microfluidic applications. A simple and versatile method of fabricating a micro-connector to have an efficient interconnection to external large-scale fluid equipment was demonstrated. To eliminate the dead volume, a capillary was bridged to a micro-channel via a connection channel, which was formed by the removal of a metal wire after the PDMS casting process. The new method does not require any adhesive, precise drilling, delicate alignment procedure and micromachining processes. It could also effectively prevent blocking of the capillaries which was commonly observed while using adhesives. With this approach, detachable and reusable micro-connectors with a minimal dead volume could be achieved. According to leakage tests, the micro-connector could withstand pressures up to 150 psi and a maximum flow rate of 50 µl min−1. The pull-out tests indicated that the PDMS fitting could provide enough mechanical strength for practical applications. Not only does this micro-connector significantly eliminate the dead volume, but it also increases the detection signal. While compared with more conventional Teflon tubing fitting, the micro-connector could reduce by at least 50% the dilution effect for sample loading analysis due to substantial elimination of the dead volume. Most importantly, this micro-connector has greater versatility for coupling capillaries to various kinds of microfluidic chips made of different materials.

Dispersion control in microfluidic chips by localized zeta potential variation using the field effect.

Abstract: A new technique to minimize the effects of turn-induced dispersion within U-shaped separation channels by using the field effect within a capacitor to vary the zeta potential along the channel walls in the vicinity of the microchannel is described. The effects of the separation channel geometry, the fluid velocity profile, and the use of the field effect to control the zeta potential on the band distribution in the detection area are extensively discussed. The results for a U-shaped separation channel indicate that varying the zeta potential by controlling the field effect significantly reduces the band dispersion induced by the 90° turns within the channel. Finally, it is shown that the application of the proposed localized zeta potential variation method also results in a correction of the band tilting phenomenon and a reduction in the racetrack effect.

Manipulation of microparticles using new modes of traveling-wave-dielectrophoretic forces: numerical Simulation and experiments

Abstract: This paper presents a microchip device which uses traveling-wave-dielectrophoretic (twDEP) forces for the manipulation of microparticles and yeast cells. The dielectrophoretic forces generated under different operating conditions are simulated numerically, and the electric field distributions, force distributions and microparticle traces are investigated thoroughly. The paper presents two innovative modes of microparticle manipulation using positive (only one electrode is active at any instant in time, while the other three electrodes are all switched off) and negative (one electrode is "off", and the other electrodes are "on") dielectrophoretic forces. Micromachining techniques are used to fabricate micro-twDEP chips. The capability of electrode arrays in manipulating bioparticles is demonstrated by driving yeast cells in a suspension medium. The current experimental data confirm that dielectrophoretic forces can be used successfully for the collection, alignment, step-wise movement and general manipulation of cells.

A new fabrication process for a flexible skin with temperature sensor array and its applications

Abstract: This paper reports a novel technique for fabrication of a flexible skin with a temperature sensor array (40×1 sensors). A simplified MEMS technology using platinum resistors as sensing materials, which are sandwiched between two polyimide layers as flexible substrates is developed. The two polyimide layers are deposited on top of a thin aluminum layer, which serves as a sacrificial layer such that the flexible skin can be released by metal etching and peeled off easily. The flexible skin with a temperature sensor array has a high mechanical flexibility and can be handily attached on a highly curved surface to detect tiny temperature distribution inside a small area. The sensor array shows a linear output and has a sensitivity of 7.5 mV/°C (prior to amplifiers) at a drive current of 1 mA. To demonstrate its applications, two examples have been demonstrated, including measurement of temperature distribution around a micro heater of a micro PCR (polymerase chain reaction) chip for DNA amplification and detection of separation point for flow over a circular cylinder. The development of the flexible skin with a temperature sensor array may be crucial for measuring temperature distribution on any curved surface in the fields of aerodynamics, space exploration, auto making and biomedical applications etc.

Integrated Microfluidic Systems for DNA Analysis

Abstract: This study reports the integration of an electrokinetically-driven micro-mixer with a on-chip temperature control system, and applies the integrated microfluidic chip to the DNA amplification process. Using the integrated chip, the cultured cells are initially broken down in a microanalysis reactor. Extracted DNA, primers and reagents are then driven electroosmotically into a mixing region where they are mixed by an electrokinetically-driven micro-mixer. The mixture is then cycled in a micro-PCR (polymerase chain reaction) chamber to perform DNA amplification. Experimental results show that the proposed device can automate the sample pretreatment operation for DNA amplification, thereby achieving significant time and effort savings. This novel integrated microfluidic device, which facilitates cell analysis, sample driving/mixing, and DNA amplification, could make a promising contribution to the continuing efforts aimed at miniaturizing bio-analysis systems

A high-speed low-voltage double-switch optical crossconnect using stress-induced bending micromirrors

Abstract: A high-speed low-voltage double-switch electrostatically actuated optical crossconnect (OXC) is demonstrated using stress-induced bending micromirrors. A curved polysilicon seesaw structure substantially lowers the electrostatic operating voltage of the OXC and provides a double-switch option. Large mirror deflection angles of 13/spl deg/ (mirror elevation of 290 /spl mu/m high) and 5/spl deg/ (cantilever deflection of 90 /spl mu/m high), corresponding to low operating voltages of 25 and 18 V, could be obtained. A submillisecond switching time (<850 /spl mu/s), a low optical insertion loss (0.65 dB), and a small polarization-dependent loss (<0.08 dB) are achieved.

Characterization of SnO2/TiO2 Double-Layer Films as Alcohol Sensing Materials

Abstract: The aim of this study is to improve the sensitivity of alcohol sensors by combining the advantages of TiO 2 and SnO 2 films in a double layer device In this study, an RF magnetron sputtering system was employed to fabricate SnO 2 /TiO 2 double-layer and SnO 2 single-layer films for applications as alcohol sensors The TiO 2 layer of the SnO 2 /TiO 2 double-layer thin film and the SnO 2 single-layer film were all deposited under various O 2 /Ar ratios of 02, 04, 06, and 08 The SnO 2 layer, the top coating of SnO 2 /TiO 2 double-layer, was deposited at a fixed O 2 /Ar ratio of 02 with an argon flow rate of 50 seem The crystal structure and surface morphology of the films were examined by X-ray diffraction (XRD), Grazing Incident X-Ray Diffraction (GID) and Scanning Electron Microscopy (SEM) The sensitivity value of the film can be calculated from the change in the resistance of the film when exposed to alcohol The results show that SnO 2 /TiO 2 double layer films have better sensitivity and quicker recovery time compared to those of single-layer SnO 2 films

Stress-Induced Bending of Micromachined Bilayer Cantilever and Its Optical Application

Abstract: In this paper, the shape effect of metal films on stress-induced bending of micromachined bilayer cantilever was first systematically investigated The cantilever makes use of residual stresses in thin films to produce a bending of micro-structures by applying preloads A finite element analysis (FEA) model was established to analyze such a deformation, with the support of experimental and theoretical results A new founding on the post-processing temperature of the micromachined structure was reported The post-processing temperature and residual stresses reveal close relations While the post-processing temperature ascends, the residual stress of the metal increases, resulting in a bigger out-of-plane deformation of the cantilever The residual stress rises to a saturated value while the temperature reaches a critical value Finally, a switchable micromachined corner mirror and a high-speed low-voltage double-switch electrostatically actuated optical crossconnect (OXC) were demonstrated using stress-induced cantilevers

A novel magnetic tweezers for manipulation of a single DNA molecule

Abstract: We report a novel magnetic tweezers for manipulation of a single DNA molecule. The micromachined DNA manipulator can stretch and rotate a single DNA molecule using arrayed microcoils. Key platform technologies including localized DNA immobilization, microcoil fabrication and microfluidics, have been integrated to form the magnetic DNA tweezers. A single DNA molecule is specifically attached onto a magnetic bead and a gold surface and manipulated under a magnetic field generated by built-in hexagonally-aligned microcoils. A highly effective method for the construction of DNA two sticky ends is developed, which is compatible with MEMS technologies. We have successfully demonstrated the rotation of the tethered-bead DNA molecule linked to the gold pattern by circular permutation of the currents applied to the microcoils.

High-throughput micro capillary electrophoresis chip for bio-analytical application utilizing multi-wavelength detection

Abstract: This paper presents a novel microfluidic device for high-throughput capillary electrophoresis (CE) analysis utilizing multi-wavelength detection. In general, fluorescent dye can only be excited using a specific range of wavelength and then it will emit specific fluorescence signal with a longer wavelength. In this study, pairs of multi-mode optic fiber are embedded at the downstream of the separation channel of the CE chips for multiple-wavelength fluorescence detection. The proposed device could detect multiple samples with different kinds of fluorescence labeling in the same channel in a single run. Experimental results show that a mixture of Rhodamine B and FITC fluorescein can be detected individually while using different kinds of light source for fluorescence excitation. Sample moving speed in the microchannel and DNA fragments are also measured and detected using the proposed device.

Method for modification of glass-based microchannel

Abstract: A method for modification of glass-based microchannels, which uses liquid organic-based solution containing siloxane for the modification of microchannels on the glass substrate, such as quartz, boron glass, sodium glass, and the like, to form a solid film to isolate the glass surface of the microchannels from the environment Therefore, the present invention can be applied for electrophoresis experiment, so that the operation causes no electrical-double-layer effects, and further eliminates the occurrence of electro-osmosis flow, thus the separation efficiency of electrophoresis chips is improved

The application of an automated oxygen concentration control and measurement system to a miniaturized energy consumption measurement system using resistive-type oxygen gas sensors

Abstract: Although the conventional indirect calorimeter is a valuable tool, its size and expense prohibits its widespread use in hospitals. Furthermore, its flow-through measurement technique dilutes the respiratory variations, and hence some form of high-precision detection instrumentation is required. These limitations may be overcome by combining MEMS with CMOS circuit design technology to develop an innovative SOC biochip as the basis of a miniaturized energy consumption measurement system. In order to measure the characteristics of the oxygen sensors which form one part of this system, this study develops an automated oxygen concentration control and measurement system. This system can simulate the miniscule respiratory variations of a premature infant and can subsequently establish a suitable oxygen concentration environment to ensure the infant's well being. The proposed system is capable of establishing environments with oxygen concentrations ranging from 5% to 100%, and can control the oxygen concentration to a resolution of 0.006%. The minimum time required to increase the oxygen concentration from 21% to 100% is approximately 5.6 seconds. The proposed system can also automatically measure the properties of the oxygen sensors, including their resistance characteristics at different oxygen concentrations, the relationship between their sensitivity and the oxygen concentration, and the influence of working temperature and humidity upon their sensitivity. The necessary measurement data is acquired locally and can then be transmitted to a remote PC via the Internet.