Characterization of microparticle separation utilizing electrokinesis within an electrodeless dielectrophoresis chip.

This study demonstrated the feasibility of utilizing electrokinesis in an electrodeless dielectrophoresis chip to separate and concentrate microparticles such as biosamples. Numerical simulations and experimental observations were facilitated to investigate the phenomena of electrokinetics, i.e., electroosmosis, dielectrophoresis, and electrothermosis. Moreover, the proposed operating mode can be used to simultaneously convey microparticles through a microfluidic device by using electroosmotic flow, eliminating the need for an additional micropump. These results not only revealed that the directions of fluids could be controlled with a forward/backward electroosmotic flow but also categorized the optimum separating parameters for various microparticle sizes (0.5, 1.0 and 2.0 µm). Separation of microparticles can be achieved by tuning driving frequencies at a specific electric potential (90 Vpp·cm(-1)). Certainly, the device can be designed as a single automated device that carries out multiple functions such as transportation, separation, and detection for the realization of the envisioned Lab-on-a-Chip idea.

Rapid whole-cell sensing chip for low-level arsenite detection.

A novel whole-cell sensing chip system consisted of a micro-concentrator, a set of electrochemical detection electrodes, and a microfluidic channel was developed for rapid detection of arsenite in water. Firstly, the E. coli cells transformed with arsenited-regulated reporter plasmids were incubated with solution contained arsenite. Under this condition, the level of reporter protein, ß-galactosidase, expressed by E. coli cells is dependent on the concentration of arsenite. Using the dielectrophoretic force, the micro-concentrator continuously enriched the E. coli cells into a small area above the embedded detection electrodes. And then the relative expression levels of ß-galactosidase were obtained using the electrochemical method to measure the amount of p-aminophenol (PAP) which converted from the p-aminophenyl-ß-D-galactopyranoside (PAPG) by ß-galactosidase. From the result, it indicates this device can detect as low as 0.1 ppm of arsenite within 30 min. Compared with other traditional detection methods, our new device provides better performance like higher sensitivity, shorter analysis time, and lower cost in detecting the arsenite.

A micro circulating PCR chip using a suction-type membrane for fluidic transport.

A new micromachined circulating polymerase chain reaction (PCR) chip is reported in this study. A novel liquid transportation mechanism utilizing a suction-type membrane and three microvalves were used to create a new microfluidic control module to rapidly transport the DNA samples and PCR reagents around three bio-reactors operating at three different temperatures. When operating at a membrane actuation frequency of 14.29 Hz and a pressure of 5 psi, the sample flow rate in the microfluidic control module can be as high as 18 microL/s. In addition, an array-type microheater was adopted to improve the temperature uniformity in the reaction chambers. Open-type reaction chambers were designed to facilitate temperature calibration. Experimental data from infrared images showed that the percentage of area inside the reaction chamber with a thermal variation of less than 1 degrees C was over 90% for a denaturing temperature of 94 degrees C. Three array-type heaters and temperature sensors were integrated into this new circulating PCR chip to modulate three specific operating temperatures for the denaturing, annealing, and extension steps of a PCR process. With this approach, the cycle numbers and reaction times of the three separate reaction steps can be individually adjusted. To verify the performance of this circulating PCR chip, a PCR process to amplify a detection gene (150 base pairs) associated with the hepatitis C virus was performed. Experimental results showed that DNA samples with concentrations ranging from 10(5) to 10(2)copies/microL can be successfully amplified. Therefore, this new circulating PCR chip may provide a useful platform for genetic identification and molecular diagnosis.