Che-Hsin Lin

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.

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 rapid three-dimensional vortex micromixer utilizing self-rotation effects under low Reynolds number conditions

This paper proposes a novel three-dimensional (3D) vortex micromixer for micro-total-analysis-systems (μTAS) applications which utilizes self-rotation effects to mix fluids in a circular chamber at low Reynolds numbers (Re). The microfluidic mixer is fabricated in a three-layer glass structure for delivering fluid samples in parallel. The fluids are driven into the circular mixing chamber by means of hydrodynamic pumps from two fluid inlet ports. The two inlet channels divide into eight individual channels tangent to a 3D circular chamber for the purpose of mixing. Numerical simulation of the microfluidic dynamics is employed to predict the self-rotation phenomenon and to estimate the mixing performance under various Reynolds number conditions. Experimental flow visualization by mixing dye samples is performed in order to verify the numerical simulation results. A good agreement is found to exist between the two sets of results. The numerical results indicate that the mixing performance can be as high as 90% within a mixing chamber of 1 mm diameter when the Reynolds number is Re = 4. Additionally, the results confirm that self-rotation in the circular mixer enhances the mixing performance significantly, even at low Reynolds numbers. The novel micromixing method presented in this study provides a simple solution to mixing problems in the lab-chip system.

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

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.

Micro capillary electrophoresis chips integrated with buried SU-8/SOG optical waveguides for bio-analytical applications

This paper reports an innovative micro electrophoresis chip, which is integrated with buried optical waveguides on glass substrates for on-line detection of bio-analytical samples. A novel buried optical waveguide structure using SU-8/SOG (spin-on-glass) double layers is demonstrated, which can increase light guiding efficiency due to large difference of refractive index between SU-8 ( n = 1.8, after hard-baking) and organic-based SOG (n = 1.36). Etched optic fibers are directly inserted into the waveguide channel for connection of light signal between microfluidic devices and peripheral optical sensors. With these novel approaches, delicate optical systems and tedious alignment procedures are not required for biomedical sample detection, resulting in a more compact or even a portable detection system. Experimental results show the developed micro capillary chip can detect Rhodamine B fluoresceins with a concentration as low as 10 −7 M by using multi-mode optic fibers as the connection of light between buried waveguides and the optical sensor. Two samples have been demonstrated to verify the performance of the chip, including a mixture of Rhodamine B and Cy 3 fluorescent dyes and FITC-labeled polypeptide samples. Both of them can be separated and detected successfully using the proposed device. The proposed device provides a cheap and simple method for on-line detection of biological samples.

A high-discernment microflow cytometer with microweir structure

Using a simple and reliable isotropic wet etching process, we fabricated a microflow cytometer in which cells/particles are concentrated in the center of the sample stream using a 2‐D hydrodynamic focusing technique and an microweir structure. Having focused the cells/particles, they are detected and counted using a LIF method. The experimental and numerical results confirm the effectiveness of the hydrodynamic sheath flows in squeezing the cells/particles into a narrow stream in the horizontal X–Y plane. Furthermore, it is shown numerically that the microweir structure results in the separation of the cells/particles in the vertical X–Z plane such that they pass through the detection region in a sequential fashion and can therefore be counted with a high degree of precision. The experimental results obtained using fluorescent polystyrene beads with diameters of 5 and 10 μm, respectively, confirm the suitability of the proposed device for microfluidic applications requiring the high‐precision counting of particles or cells within a sample flow.

Multi-cell-line micro flow cytometers with buried SU-8/SOG optical waveguides

This paper reports a micro flow cytometer integrated with an innovative buried optical waveguide on soda-lime glass substrates. A novel optical waveguide using SU8/SOG (spin-on-glass) double-layer structure was demonstrated. The light guiding efficiency was improved due to smoother channel surface and larger difference of refractive index between SU-8 and organic-based SOG. Instead of using complicated optical alignment system, detection light source was coupled into the waveguide by directly inserting an etched optical fiber. A very high coupling efficiency could be achieved by this approach. In this study, the performance of the waveguides and insertion losses of the chip were measured. Results showed that the optical loss was less than 15 dB for a 40-mm long waveguide. The buried optical waveguide provides a built-in detection source for cell counting. Preliminary results indicated that a multi-cell-line flow cytometer with built-in detection system could be realized.

Double-L injection technique for high performance capillary electrophoresis detection in microfluidic chips

This paper reports low-leakage injection techniques to deliver sample plugs within double-T-form electrophoresis microchips. Experimental and numerical investigations are used to predict and evaluate the leakage behavior during electrokinetic driving of the sample plugs. The principal material transport mechanisms including traditional cross-form, electro-floating, diffusion sampling injection techniques are discussed in this study. A simple and precise double-L injection technique that employs electrokinetic manipulations to avoid sample leakage within the microchip is also reported. The method needs only one electrical control point during injection and separation, so the control system can be smaller and cheaper. Experimental and numerical results show the proposed injection technique is able to reduce sample leakage significantly. No leakage happens after 16 sample injections using the double-L injection method while leakage usually happens using the traditional cross-form injection technique. The double-L injection technique proposed in this study has a great potential for use in high-precision analysis applications utilizing chip-based capillary electrophoresis.

Integrated microfluidic chip for rapid DNA digestion and time-resolved capillary electrophoresis analysis.

An integrated microfluidic chip is proposed for rapid DNA digestion and time-resolved capillary electrophoresis (CE) analysis. The chip comprises two gel-filled chambers for DNA enrichment and purification, respectively, a T-form micromixer for DNA/restriction enzyme mixing, a serpentine channel for DNA digestion reaction, and a CE channel for on-line capillary electrophoresis analysis. The DNA and restriction enzyme are mixed electroomostically using a pinched-switching DC field. The experimental and numerical results show that a mixing performance of 97% is achieved within a distance of 1 mm from the T-junction when a driving voltage of 90 V/cm and a switching frequency of 4 Hz are applied. Successive mixing digestion and capillary electrophoresis operation clearly present the changes on digesting φx-174 DNA in different CE runs. The time-resolved electropherograms show that the proposed device enables a φx-174 DNA sample comprising 11 fragments to be concentrated and analyzed within 24 min. Overall, the results presented in this study show that the proposed microfluidic chip provides a rapid and effective tool for DNA digestion and CE analysis applications.

Experimental and numerical estimations into the force distribution on an occlusal surface utilizing a flexible force sensor array

This study presents a novel flexible force sensor array for measuring the distribution of the force distribution over the first molar. The developed force sensor array is composed of a flexible polyimide electrode and barium-titanate-based multilayer ceramic capacitors (MLCCs). The piezoelectric and material properties of industrial-grade MLCCs are ideal for measuring large-force loadings. The sensors are cheap and easy to integrate with automated manufacturing processes. Prior to experimental measurements, the force responses for the MLCC sensor cells were systematically measured and evaluated, confirming their high fracture strength and good sensing properties. Finite element (FE) simulations were used to calculate the force distribution over the tooth crown from the measurement results of the 3×3 force sensor array. Results indicate that the sensor has great sensitivity and linearity under a high-speed cycle loading of 500 N/s conducted to simulate normal chewing. The total force measured using the developed sensor array within the artificial tooth had an error of less than 5%. In addition, the force distributions over the molar crown obtained using a numerical method of FE analysis agree well with those obtained from experiments. The developed flexible force sensor array thus has potential for in-situ bite force measurements that are low-cost and reliable.