Cheng-Wey Wei

Crack-free direct-writing on glass using a low-power UV laser in the manufacture of a microfluidic chip

Glass is an excellent material for use as a microfluidic chip substrate because it has great chemical and thermal stability. This work describes a flexible platform for the rapid prototyping of microfluidic chips fabricated from glass. A debris-free laser direct-writing technology that requires no photomask generation is developed. A 266 nm laser with a high repetition rate is employed in laser-induced backside wet etching (LIBWE) for glass machining. A microfluidic pattern is designed using computer drawing software and then automatically translated into computer numerical control motion so that the microtrench is directly fabricated on the glass chip. The overall machining speed can be increased by increasing the repetition rate to ~6 kHz. Without a clean room facility or the highly corrosive acid, HF, the overall development time is within hours. Trenches with complex structures that are hard to fabricate by photolithography were easily produced by laser direct-writing. An integrated microreactor/concentrator is demonstrated. The crack-free and debris-free surface was characterized by SEM and a surface profiler. Various effective etching chemicals for the LIBWE process were investigated to understand the etching mechanism. The minimal laser power used for glass etching was approximately 20 mW for a 6 µm wide microtrench. Several new compounds have been demonstrated to be effective in ablation. The etch threshold is minimum and does not decrease further as the unit length absorbance increases above 8000 in acetone solution.

Rapid cell-patterning and microfluidic chip fabrication by crack-free CO2 laser ablation on glass

This paper uses a widely available CO2 laser scriber (λ = 10.6 µm) to perform the direct-writing ablation of quartz, borofloat and pyrex substrates for the development of microfluidic chips and cell chips. The surface quality of the ablated microchannels and the presence of debris and distortion are examined by scanning electron microscopy, atomic force microscopy and surface profile measurement techniques. The developed laser ablation system provides a versatile and economic approach for the fabrication of glass microfluidic chips with crack-free structures. In the laser writing process, the desired microfluidic patterns are designed using commercial computer software and are then transferred to the laser scriber to ablate the trenches. This process eliminates the requirement for corrosive chemicals and photomasks, and hence the overall microchip development time is limited to less than 24 h. Additionally, since the laser writing process is not limited by the dimensions of a photomask, the microchannels can be written over a large substrate area. The machining capability and versatility of the laser writing system are demonstrated through its application to the fabrication of a borofloat microfluidic chip and the writing of a series of asymmetric trenches in a microwell array. It is shown that the minimum attainable trench width is 95 µm and that the maximum trench depth is 225 µm. The system provides an economic and powerful means of rapid glass microfluidic chip development. A rapid cell-patterning method based on this method is also demonstrated.

ELECTROOSMOTIC MIXING INDUCED BY NON-UNIFORM ZETA POTENTIAL AND APPLICATION FOR DNA MICROARRAY IN MICROFLUIDIC CHANNEL

In this study, we describe a modification of the conventional microarray format. 20-mer oligonucleotide probes and singly labeled 20-mer targets, representative of the T-cell acute lymphocytic leukemia 1 (TAL1) gene, has been used to elucidate the performance of this hybridization approach. DNA microarray is integrated with microfluidic channel on a poly(methyl methacrylate) (PMMA) to generate non-uniform zeta potential inside the channel. A microtrench is designed and fabricated on a PMMA chip using a widely available CO2 laser scriber The electroosmotic mixing effect induced by the non-uniform zeta potential is utilized to enhance the DNA-DNA hybridization. The flow field in microfluidic channel is measured by particle image velocimetry (PIV). The enhanced signal to noise (S/B) ratio and reduced hybridization time is observed when the electroosmotic mixing is applied in the DNA-DNA hybridization.

Crack-free laser direct-writing on quartz and glass for microfluidic chip development

We present a flexible microfluidic channel fabrication platform that can be used to develop microfluidic chips. A DPSS (diode pumped solid state) frequency quadrupled (λ = 266 nm, the UV system) Nd:YAG laser and a CO2 laser (λ = 10.6 μm, the IR system) are compared for their ablation capability on quartz and glass. We have also compared their performance in developing microfluidic chips. The resultant surface quality, including microcracking, debris, and distortion, is examined by SEM and a surface profiler. In these systems, users design microfluidic patterns by commercial software. The pattern is then transferred to a CNC stage for trenching. The microfabrication process can be completed in several minutes. Without the need to fabricate photomask for patterning, the development time can be reduced from weeks to hours. In addition, the substrate size is not limited by the dimension of the photomask. Asymmetric trenches demonstrating the machining capability of these systems have been fabricated by these systems. The minimal feature for the IR system and the UV system is 140 μm and 5 μm, respectively. These systems are very powerful for rapid glass microfluidic chip development.

Innovative Laser Machining and Surface Modification for Plastic Microfluidic Chip

An innovative plastic machining and accompanying surface modification method has been developed for rapid microfluidic chip manufacturing on poly(methyl methacrylate) substrate. The method provides an economic and swift way to fabricate microfluidic channels with various aspect ratios using a widely available CO2 laser. The machined surface has been modified to introduce functional group. The surface smoothness is also greatly enhanced with thermal annealing after laser machining. Several microfluidic patterns have been prepared to demonstrate the capability and flexibility of this method.

The Integration of Microarray and Microchannel Using Plastic Chip

A novel microarray platform is being developed. The strategy involves embedding microarry into microfluidic channel to overcome some drawbacks of microarray. The use of a poly(methyl methacrylate) (PMMA)-based microfluidic channel can be conveniently micromachined using a widely available CO2 laser scriber. The expected benefits of incorporating microarray into microchannel includes reduced sample amount, enhanced detection limit and minimized data variation. For immobilization of DNA on the PMMA surface, the chip surface is modified with reducing reagents to convert the ester group on PMMA surface into hydroxyl linkage. The resultant hydroxyl linkage renders the PMMA surface suitable for silanization chemistry widely used in glass surface treatment for DNA and protein immobilization.

A microfluidic coculture system for cell-cell interaction study

A novel microfluidic coculture system was developed for more accurately modelling the interaction of macrophages and osteoblasts. The microfluidic coculture chip was fabricated by CO/sub 2/ laser direct-writing on poly(methyl methacrylate) (PIMMA) and was designed to separate two cell types by a microchannel, while permitting cellular media to transfer. The released inflammatory cytokines (ex: IL-I/spl beta/, TNF-/spl alpha/ activated in upstream macrophages flow through a microfluidic system and generate linear concentration gradients in down-stream wells and induce down-stream osteoblasts to release prostaglandin E2 (PGE2), which is well-known as a bone resorption marker. Colorimetric MTT assay was used to examine the osteoblast viability. This system can be used to evaluate the cell-cell interaction while physically separate the interacting cells.