Yung-Chiang Chung

Microfluidic chip of fast DNA hybridization using denaturing and motion of nucleic acids

This study presents the effect of fluidic temperatures and velocities on improving DNA hybridization. The efficiency of hybridization could be improved by introducing elevated temperature in the hot region and velocity in the cold region. Compared with the conventional methods, this hybridization microchip was able to increase the hybridization signal 4.6‐fold within 30 min. The 1.4‐kb single‐stranded target DNA was tested. The increasing tendency of the fluorescence intensity was apparent when the temperature was higher than 82°C, and the fluorescence intensity reached an asymptotic value at T >90°C. A mathematical model was proposed to relate the fluorescence intensity of DNA hybridization with the hot‐region temperature and the cold‐region velocity. Based on these results, the new hybridization chip with the processes of temperature and velocity differences will improve efficiency of DNA detection. The microchip combined with hot‐region temperature and cold‐region bulk flow velocity effects could provide additional efficiency in DNA hybridization.

The effect of velocity and extensional strain rate on enhancing DNA hybridization

A study of the effect of fluidic velocities and extensional strain rates on DNA hybridization microchips was conducted. The hybridization efficiency could be improved by introducing velocity and extensional strain rate. Compared with conventional hybridization methods, this microchip was able to increase the hybridization signal nine-fold within 30 min. Three different devices were designed, fabricated and tested using 1.4 kb single stranded DNA as the target. Excellent correlation between simulation analysis and experimental data was obtained. Experimental results showed that the effect of extensional strain rate on the hybridization was larger than that of velocity. Based on this information, a new design of hybridization chip with microfluidic concepts of velocity and extensional strain rate may provide additional efficiency in DNA detection. This hybridization microchip can provide potential applications in genomic study in the future.

Fabrication and testing of surface ratchets primed with hydrophobic parylene and hexamethyldisilazane for transporting droplets

We demonstrate a way to transport droplets by an arrowed micropillar array surface with hydrophobic parylene. The lightly hydrophilic parylene surface could be changed to hydrophobic one by treating with fluorine-based plasma (CF4 or SF6). The droplet on this hydrophobic parylene surface with arrowed ratchets could be transported by a speaker, and the average measured velocity was 29 mm/s. Moreover, the authors compared driving performance of the parylene surface ratchets with the ones modified by the hexamethyldisilazane (HMDS) vapor. Both the results of using hydrophobic parylene and HMDS were better than the previous work.

Comparison of different metal film thicknesses of cyclic olefin copolymer–substrate polymerase chain-reaction chips with single-side and double-side heaters

The polymerase chain reaction (PCR) chips of different metal film thicknesses were fabricated, and the PCR machine with/without a top heater and the single-side/double-side heater PCR chips were compared. Before fabricating the chips, one simulated the effect of various thin-film thicknesses and the temperature distributions of various powers, and it helped one to find the optimum parameters. The total substrate material was cyclic olefin copolymers, and the gold film was fabricated on the substrate by evaporation. The results after PCR for the deoxyri bonucleic acid (DNA) of an Escherichia coli TG-1 cell were obtained. The results of the DNA amplifying 225 bps were 0.84-0.92 ng/µl, and these were 78-85% of the result of PCR machine with a top heater. There was no PCR product in the PCR machine without a top heater and single-side PCR chip. The thermal deformation temperature, thermal conductivity, and substrate thickness are the important parameters in a polymer substrate PCR chip, and the thermal deformation temperature is the key parameter.

Experimental Verification of A Bi-Directional Driving System for Microfluids

A bi-directional microfluidic driving system was developed experimentally in this work. The bi-directional driving module combines two individual components for suction and exclusion. The individual components can be combined using a T-shape connection as well as in parallel. Modular devices with a parallel connection, presented herein, can provide flexible, predictable and linear control of bi-directional microfluid pumping. This work demonstrated the driving system and investigated the influences of the characteristics of the working liquids. The driving force, both suction and exclusion, for the liquid with the lower viscosity is stronger than those with the higher viscosity. Furthermore, the required flow rate at the suction component is quite large due to the strong surface tension of water.

A new vortex-based device using dragonfly wing to reduce the chip size

This work presents a new vortex-based flow device. A corrugated dragonfly wing blocks in a microchannel of 250 µm wide good to capture particles and to reduce the chip size. Two conclusions have been found. The new flow chips made of PDMS and their microbes filling experiments firstly revealed that only one dragonfly wing in the channel works in particle capture but without choking. Secondly, COMSOL-Multiphysics simulation of the new design using dragonfly wing predicted that the reduced entrance channel length by 50% was achieved by adding a dragonfly wing to the previous design by Sollier. This new design of vortex-based devices is good for the integration and application for tumor cell collection, capture and sorting in the future.

Improvement for gene transfection of bacteria using magnetic attraction

We propose cells can be descended using magnetic attraction, which leads to shorter experimental time and higher efficiency. We used an electroporation chip with adjustable electromagnetic field as the experimental platform, and tested Escherichia coli and 6-nm magnetic beads combined with DNA plasmid. The magnetic beads were positively charged and easy to bind to the negatively charged cell membrane of E. coli. The magnetic beads and E. coli could be attracted quickly to the bottom because of the electromagnet and could reduce operational time and enhance transfection efficiency. After electroporating and culturing, we obtained the results for E. coli with drug resistance and calculated the number of colony as the transfection efficiency. The achieved transfection efficiency using magnetic beads was seven-fold higher than that without magnetic bead. The following optimum parameter values were determined: 1.4 × 1014 bead/ml for nano-magnetic bead concentration, 200 Gauss for magnetic flux density, and 40 s for magnetic attraction lasting time. The results will help develop transfection applications for low-descent-velocity cells.

Effect of magnetic attraction on gene transfection of bacteria

We propose cells can be descended using magnetic attraction, which leads to shorter experimental time and higher efficiency. We used an electroporation chip with adjustable electromagnetic field as the experimental platform, and tested Escherichia coli and 6-nm magnetic beads combined with DNA plasmid. The magnetic beads were positively charged and easy to bind to the negatively charged cell membrane of E. coli. The magnetic beads and E. coli could be attracted quickly to the bottom because of the electromagnet and could reduce operational time and enhance transfection efficiency. After electroporating and culturing, we obtained the results for E. coli with drug resistance and calculated the number of colony as the transfection efficiency. The achieved transfection efficiency using magnetic beads was seven-fold higher than that without magnetic bead. The following optimum parameter values were determined: 1.4 × 1014 bead/ml for nano-magnetic bead concentration, 200 Gauss for magnetic flux density, and 40 s for magnetic attraction lasting time. The results will help develop transfection applications for low-descent-velocity cells.

The relationship between stretching and force of dsDNA molecules at various temperatures by using magnetic tweezers

Stretching experiments on lambda-DNA were carried out in a microfluidic channel using an inverted fluorescence microscope, micro-flow pump, and electromagnet. The micro-flow channel was fabricated by using micro electromechanical system technology, and the micro electromagnet was analyzed by computer software to simulate the magnetic field distribution. The magnetic field was 248.6 gauss at a current of 0.5 A and the system could exert 20.4 pN of force on a magnetic bead with a diameter of 2.8 μm. When the temperature of the buffer was 25 °C, the average length of lambda-DNA molecules was 1.9 μm without the magnetic field. In a magnetic field of 248.6 gauss, the extension of lambda-DNA molecules was 7.2 μm, the total length was 9.1 μm, and the coefficient of elasticity was 2.83 × 10-6 N/m. When the buffer temperature was increased to 45 °C, the average length of lambda-DNA molecules was 4.6 μm in the absence of a magnetic field. At 45 °C in a magnetic field of 248.6 gauss, the extension of lambda-DNA molecules was 11.9 μm, the total length was 16.5 μm, and the coefficient of elasticity was 1.71 × 10-6 N/m. This system can be applied to the measure the extension and coefficient of elasticity of macromolecules.

Particles sorting in micro-channel using magnetic tweezers and optical tweezers

This study evaluates a method for separating magnetic microparticles in a micro channel by using embedded inverted-laser tweezers, a microflow pump, and a micro magnet. Various particles were separated using optical and/or magnetic tweezers, and were identified and counted to determine the dependence of the sorting rate on the channel flow velocity. The particle sorting experiment showed good separation results when the designed channel and magnetic tweezers were used. For magnetic particles, lower flow velocities corresponded to larger separating rates with a maximum separating rate of 81%. When the designed channel and optical tweezers were used, the polystyrene particle separating rate was as high as 94%. When both the optical tweezers and the magnetic tweezers were used, the optical tweezers were more effective in trapping polystyrene particles with flow velocities between 0.09 and 0.25μm/s. For flow velocities between 0.09 and 0.17 μm/s, the separating rate for polystyrene particles reached 95% and the separating rate for magnetic particles reached 85%.