Yu-Jen Pan

A glass microfluidic chip adhesive bonding method at room temperature

This paper presents a novel method using UV epoxy resin for the bonding of glass blanks and patterned plates at room temperature. There is no need to use a high-temperature thermal fusion process and therefore avoid damaging temperature-sensitive metals in a microchip. The proposed technique has the further advantage that the sealed glass blanks and patterned plates can be separated by the application of adequate heat. In this way, the microchip can be opened, the fouling microchannels may be easily cleaned-up and the plates then re-bonded to recycle the microchip. The proposed sealing method is used to bond a microfluidic device, and the bonding strength is then investigated in a series of chemical resistance tests conducted in various chemicals. Leakage of solution was evaluated in a microfluidic chip using pressure testing to 1.792 × 102 kPa (26 psi), and the microchannel had no observable leak. Electrical leakage between channels was tested by comparing the resistances of two bonding methods, and the result shows no significant electrical leakage. The performance of the device obtained from the proposed bonding method is compared with that of the thermal fusion bonding technique for an identical microfluidic device. It is found that identical results are obtained under the same operating conditions. The proposed method provides a simple, quick and inexpensive method for sealing glass microfluidic chips.

Electrokinetic flow focusing and valveless switching integrated with electrokinetic instability for mixing enhancement

This study performs an experimental investigation into electrokinetically-driven flow phenomena in microfluidic chips. The study commences by investigating the electrokinetic focusing/valveless switching of multiple sample flows in an M × N microfluidic chip, where M is the number of sample streams and N is the number of outlet channels. The experimental results show that the sample flows can be electrokinetically pre-focused into narrow streams via sheath flows and then guided to the desired outlet ports by applying a simple voltage control model which specifies the intensity of the external electrical field to be applied to the inlet channels and the required potential conditions of the individual outlet channels, i.e. grounded or isolated. The study then investigates the electrokinetic instability phenomenon induced at the interfaces between the sample flows and the sheath flows by the application of an external electrical field of sufficient intensity. It is shown that inducing this instability phenomenon yields a significant improvement in the mixing performance within the microchannel. Finally, it is demonstrated that by applying a high electrical potential to the inlet channel and specifying appropriate potential conditions for the individual outlet channels, two sample streams can be directed to any one of the N outlet channels in order to carry out mixing via electrokinetic instability effects.

Transient analysis of electro-osmotic secondary flow induced by dc or ac electric field in a curved rectangular microchannel

This study investigates transient secondary flow in a rectangular curved microchannel in which the fluid is driven by the application of an external dc or ac electric field. The resultant flow field evolutions within the microchannel are simulated using the backwards Euler time stepping numerical method in order to clarify the relationship between the changes in the transverse flow field conditions and the intensity of the applied electric field. The transient secondary flow evolutions provide evidence of the growth and decay of vortices in the transverse section. As the applied dc or ac electric field intensity is activated, a small vortex appears in each corner of the microchannel. Both upper and lower corner vortices gradually grow in size and strength and finally merge to form a single vortex, which compresses the original recirculation in the upper and lower half of the transverse section. In this study, the formation of these vortices is investigated through total applied force per unit area existing in the flow. The velocity magnitude of the vortices can be as high as 15% of the core axial speed.

M/spl times/N micro flow switches using electrokinetic forces

This paper presents experimental and numerical investigation on electrokinetic-focusing 1/spl times/N (1 sample inlet-port and N outlet-ports) and M/spl times/N (M sample inlet-ports and N outlet-ports) flow switches for bio-analytical applications. The microfluidic device integrates two important microfluidic phenomena, including electrokinetic-focusing and valveless flow switching inside multi-ported microchannels. A voltage control model is proposed, which achieves electrokinetic focusing/switching in a pre-focusing flow switch system. Using the developed methods, the sample can be electrokinetically pre-focused to a narrow stream and can be continuously injected into desired outlet ports. The microfluidic chip presented here is promising for high-throughput chemical analysis, cell fusion, fraction collection, fast sample mixing and many other applications in the field of micro-total-analysis systems.

An investigation of the effects of inlet channel geometry on electrokinetic instabilities

Numerical and experimental investigations are performed to examine the feasibility of inducing electrokinetic instability (EKI) phenomena in two-channel junctions containing two aqueous electrolytes with a 10:1 conductivity ratio via the application of a low-intensity DC electrical field. A deep microchannel with 700 μm in depth and 100 μm in width was designed, fabricated and used in this investigation. The results show that when the species streams are injected such that the conductivity gradient between them is perpendicular to the DC electrical driving field, an EKI effect can only be induced by applying a high electrical field intensity of 0.54 V/cm. However, when the potentials applied to the reservoirs of the microchip are switched such that the conductivity gradient is not perpendicular to the electrical field, flow instability can be achieved by applying a lower electrical field intensity.