Gwo-Bin Lee

The hydrodynamic focusing effect inside rectangular microchannels

This paper presents a theoretical and experimental investigation into the hydrodynamic focusing effect in rectangular microchannels. Two theoretical models for two-dimensional hydrodynamic focusing are proposed. The first model predicts the width of the focused stream in symmetric hydrodynamic focusing in microchannels of various aspect ratios. The second model predicts the location and the width of the focused stream in asymmetric hydrodynamic focusing in microchannels with a low or high aspect ratio. In both models, the theoretical results are shown to be in good agreement with the experimental data. Hence, the models provide a useful means of performing a theoretical analysis of flow control in microfluidic devices using hydrodynamic focusing effects. The ability of the proposed models to control the focused stream within a micro flow cytometer is verified in a series of experimental trials performed using polystyrene microparticles with a diameter of 20 µm. The experimental data show that the width of the focused stream can be reduced to the same order of magnitude as that of the particle size. Furthermore, it is shown that the microparticles can be successfully hydrodynamically focused and switched to the desired outlet port of the cytometer. Hence, the models presented in this study provide sufficient control to support cell/particle counting and sorting applications.

Integrated microfluidic systems for cell lysis, mixing/pumping and DNA amplification

The present paper reports a fully automated microfluidic system for the DNA amplification process by integrating an electroosmotic pump, an active micromixer and an on-chip temperature control system. In this DNA amplification process, the cell lysis is initially performed in a micro cell lysis reactor. Extracted DNA samples, primers and reagents are then driven electroosmotically into a mixing region where they are mixed by the active micromixer. The homogeneous mixture is then thermally cycled in a micro-PCR (polymerase chain reaction) chamber to perform DNA amplification. Experimental results show that the proposed device can successfully automate the sample pretreatment operation for DNA amplification, thereby delivering significant time and effort savings. The new microfluidic system, which facilitates cell lysis, sample driving/mixing and DNA amplification, could provide a significant contribution to ongoing efforts to miniaturize bio-analysis systems by utilizing a simple fabrication process and cheap materials.

A magnetic bead-based assay for the rapid detection of methicillin-resistant Staphylococcus aureus by using a microfluidic system with integrated loop-mediated isothermal amplification

This study reports a new diagnostic assay for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) by combing nucleic acid extraction and isothermal amplification of target nucleic acids in a magnetic bead-based microfluidic system. By using specific probe-conjugated magnetic beads, the target deoxyribonucleic acid (DNA) of the MRSA can be specifically recognized and hybridized onto the surface of the magnetic beads which are then mixed with clinical sample lysates. This is followed by purifying and concentrating the target DNA from the clinical sample lysates by applying a magnetic field. Nucleic acid amplification of the target genes can then be performed by the use of a loop-mediated isothermal amplification (LAMP) process via the incorporation of a built-in micro temperature control module, followed by analyzing the optical density (OD) of the LAMP amplicons using a spectrophotometer. Significantly, experimental results show that the limit of detection (LOD) for MRSA in the clinical samples is approximately 10 fg μL(-1) by performing this diagnostic assay in the magnetic bead-based microfluidic system. In addition, the entire diagnostic protocol, from bio-sample pre-treatment to optical detection, can be automatically completed within 60 min. Consequently, this miniature diagnostic assay may become a powerful tool for the rapid purification and detection of MRSA and a potential point-of-care platform for detection of other types of infections.

A cell counting/sorting system incorporated with a microfabricated flow cytometer chip

Flow cytometry is a popular technique for counting and sorting individual cells. This study presents and demonstrates a new cell counting/sorting system integrated with several essential components including a micromachined flow cytometer chip device, an optical detection system and a data analysis and control system to achieve the functions of cell sample injection, optical signal detection and cell collection. By using MEMS technology, we have integrated several microfluidic components such as micro pneumatic pumps/valves onto a polymer-based chip device. Three pneumatic micropumps are used to provide the hydrodynamic driving force for both sample and sheath flows such that hydrodynamic flow focusing can be achieved, and a micro flow switch device comprising three pneumatic microvalves located downstream of the micro sample flow channel is used for cell collection. Cell samples of human lung cancer cells labelled with commercially available fluorescent dyes have been detected and collected successfully utilizing the developed device. The real-time image of dye-labelled cell samples being excited and detected can be monitored and observed through the LCD panel by a custom designed CCD/APD holder and moving stage. Finally, micro flow switch devices were used to successfully sort the cells into the desired outlet channel, and the counting results of the specific cell samples were monitored through the counting panel. The current study focuses on the setup of the overall system. The proposed flow cytometer system has several advantages such as portability, low cost and easy operation process. The size of the system is 37 cm × 16 cm × 18 cm and the weight is 3.5 kg. The error rate of counting and sorting was 1.5% and 2%, respectively. The sorting frequency of the microvalve device is calculated to be 120 cells min−1. The developed microfluidic chip device could be a promising tool for cell-based application fields such as profiling, counting and sorting.

Micro flow cytometers with buried SU-8/SOG optical waveguides

This paper reports an innovative micromachine-based flow cytometer integrated with buried optical waveguides on soda-lime glass substrates. A novel optical waveguide using SU-8/spin-on-glass (SOG) double-layer structure is demonstrated, which increases light guiding efficiency due to smoother channel surface and larger difference of refractive index between SU-8 and organic-based SOG. Instead of using complex optical alignment system, detection light source is coupled with the waveguide with direct insertion of an etched optical fiber. A very high coupling efficiency can be achieved using this approach. In this study, the performance of the waveguides and insertion losses are measured. Experimental results show that the optical loss is less than 15 dB for a 40 mm long waveguide. With the integrated optical waveguides, a micro flow cytometer capable of particle counting has been realized. Data show that microparticles can be hydrodynamically focused and counted successfully without fluorescent labeling using the miniaturized flow cytometer with the integrated optical detection system.

Micromachine-based humidity sensors with integrated temperature sensors for signal drift compensation

This paper presents a novel technique for the fabrication of a micro humidity sensor with suspending structures. A MEMS device is developed which uses thin-film platinum resistors as temperature sensing elements and a nitride/silicon microstructure suspended at a small distance above the surface of a glass substrate as the movable electrode of a capacitor. A mechanism is proposed for the measurement of the capacitance between the suspended wafer structure and the glass substrate for different values of relative humidity. The fundamental component of the micromachine-based humidity sensor is a nitride/silicon cantilever coated with a vapor-absorbent polymer film (polyimide). A variation in humidity causes moisture-dependent bending of the microcantilever, which changes the measured capacitance between the microcantilever and the substrate. The current experimental data show that the low stiffness of the microcantilever and the large electrode area on the microcantilever tip yield a high degree of sensitivity, i.e. 2.0 nF/% RH. To compensate for the temperature drift of the capacitance signals, the proposed humidity sensor is integrated with a micro resistance-type temperature detector comprised of platinum resistors. The experimental data indicate a low hysteresis value at high relative humidity (>65% RH). The relationship between the measured resistance/capacitance and relative humidity is fully explored and documented. The numerical and experimental samples all indicate a high degree of linearity (R2 = 0.9989), a high stability (±0.76%) and a reasonable response time (1.10 s).

Hydrodynamic Focusing for a Micromachined Flow Cytometer

This paper describes hydrodynamic focusing inside a micromachined flow cytometer. Flow cytometry is a process whereby cells are analyzed and sorted based on hydrodynamic focusing phenomenon and specific cellular characteristics. In this study, the hydrodynamic focusing phenomenon is first modeled by employing potential flow theory. Then the flow field inside the flow cytometer is numerically simulated. The effect of the device geometry and relative sheath and sample flow rate on the focusing of the center flow is explored systematically. At last, a micromachine-based flow chamber is designed and fabricated on plastic substrates as a micro flow cytometer. Hydrodynamic focusing is verified with the use of microscopic visualization of water sheath flows and dyecontaining sample flow. Experimental data indicate that the size of focused sample stream can be reduced to about 3mm, which is applicable to cell sorting and counting. @DOI: 10.1115/1.1385514#

Micro flow cytometry utilizing a magnetic bead-based immunoassay for rapid virus detection☆

The current study presents a new miniature microfluidic flow cytometer integrated with several functional micro-devices capable of viral sample purification and detection by utilizing a magnetic bead-based immunoassay. The magnetic beads were conjugated with specific antibodies, which can recognize and capture target viruses. Another dye-labeled anti-virus antibody was then used to mark the bead-bound virus for the subsequent optical detection. Several essential components were integrated onto a single chip including a sample incubation module, a micro flow cytometry module and an optical detection module. The sample incubation module consisting of pneumatic micropumps and a membrane-type, active micromixer was used for purifying and enriching the target virus-bound magnetic beads with the aid of a permanent magnet. The micro flow cytometry module and the optical detection module were used to perform the functions of virus counting and collection. Experimental results showed that virus samples with a concentration of 10(3)PFU/ml can be automatically detected successfully by the developed system. In addition, the entire diagnosis procedure including sample incubation and virus detection took only about 40min. Consequently, the proposed micro flow cytometry may provide a powerful platform for rapid diagnosis and future biological applications.

Micromachined flow cytometers with embedded etched optic fibers for optical detection

This paper presents a device that integrates a micromachined flow cytometer with two embedded etched optic fibers in order to carry out on-line detection of particles and cells. A simple and reliable fabrication process is used to fabricate the cytometer on soda-lime glass substrates. It is shown experimentally that particles/cells can be squeezed hydrodynamically into a narrow stream by two neighboring sheath flows such that they flow individually through a detection region. The resulting scattered light is then detected by etched optic fibers downstream. The proposed approach has the advantage that particles/cells can be counted without the need for fluorescent labeling or delicate optical alignment procedures. The current study confirms the success of the proposed microchip in the counting of polystyrene beads and human blood cells. The results also indicate that the intensity of the scattered light is proportional to the size of the particles/cells, which suggests that the proposed device may offer the potential to distinguish between particles/cells of different sizes.

A flexible MEMS technology and its first application to shear stress sensor skin

A new microfabrication technology that enables the integration of MEMS devices on a flexible polyimide skin has been developed. Mechanically, the flexible skin consists of many individual Si islands (necessary for silicon MEMS/electronics devices) that are connected together by a thin/thick polyimide film (typically 1-100 /spl mu/m thick). To create the islands, Si diaphragms are first formed with a desirable thickness (10-500 /spl mu/m) by Si wet etching and then patterned from the back side by reactive ion etching (RIE). As a first application, flexible shear-stress sensor skins for aerodynamics study have been fabricated. The finished skin is 3 cm long and 1 cm wide, and it consists of about 100 sensors. The skin polyimide is 17 /spl mu/m thick and the silicon islands are 75 /spl mu/m thick. These skins have been successfully taped on a semi-cylindrical (1.3 cm diameter) delta wing leading edge to perform real-time 2-D shear stress profiling.