Yick Chuen Chan

High-throughput design and fabrication of an integrated microsystem with high aspect-ratio sub-micron pillar arrays for free-solution micro capillary electrophoresis

A new technology approach for the design, fabrication and application of an integrated free-solution capillary electrophoresis microsystem is presented. Combining the advantages of projection, contact photolithography and deep-reactive-ion-etching, this approach allows fast and flexible formation of micron-sized channels integrated with extremely high aspect-ratio (>50:1) sub-micron pillar arrays on a silicon substrate. Utilizing fluorescence video microscopy, free-solution DNA separation has been demonstrated. Furthermore, the detailed DNA molecular interaction with the pillars inside the microsystem can be analysed. In comparison with the previously reported fabrication technologies, such as electron beam lithography, the newly presented technology approach offers a significant improvement in fabrication time and design flexibility; both are highly desirable not only for potential commercialization of the free-solution electrophoresis microsystem in applications such as lab-on-a-chip but also for systematic studies of micro-scale DNA kinetics.

Design and fabrication of an integrated microsystem for microcapillary electrophoresis

A capillary electrophoresis microsystem integrated with feed-through platinum electrodes was designed and fabricated for the separation of DNA fragments. A novel glass-to-silicon bonding technology, which allows anodic bonding of a glass wafer to a silicon wafer coated with a thick dielectric film by the inclusion of a thin intermediate amorphous silicon layer, was developed and employed to construct the microsystem. Despite the existence of a thick insulating material and non-uniform topography, robust devices without fluid leakage were obtained. Electrophoretic manipulation and separation of DNA fragments after capillary pre-treatment have been demonstrated and several operational considerations are discussed. The system performance suggests that silicon-based microsystems can be advantageous and practical for the fabrication of integrated microcapillary electrophoresis devices.

Effects of embedded sub‐micron pillar arrays in microfluidic channels on large DNA electrophoresis

A study of the influences of embedding artificial structures in a microfluidic device for CE with a free buffer solution is presented. Compared with conventional slab‐gel electrophoresis, three major additional effects on the overall system performance are identified when sub‐micron pillar arrays are integrated into a standard CE microsystem. Since DNA molecules have to migrate in‐between and interact with the pillars, pillar geometry is first demonstrated to have a direct impact on the DNA motion pattern. Electric field re‐distribution is another inevitable outcome when features of sub‐micron dimensions are placed inside a microchannel. This effect is verified by a numerical simulation tool. Furthermore, the integration of the closely packed sub‐micron structures dramatically increases the surface to volume ratios in the microfluidic device and therefore generates a large EOF. The consequence of these additional influences implies a complexity in the measured DNA velocity and indicates that careful considerations have to be taken when these devices are used for DNA electrokinetics study or electrophoresis theory re‐examination.

DNA kinetics in microfabricated devices

The DNA kinetics in micro-capillary electrophoresis is presented. The mobility and diffusion coefficient of 14bp-DNA fragments as a function of concentration in two types of separation sieving matrices, hydroxyethylcellulose (HEC) polymer solution and agarose gel, are extracted through a series of experiments performed in microfabricated devices. In addition, the motion of a DNA plug through a miter bend and splitting a plug in a branch are quantitatively characterized. The concept of equivalent length is introduced to quantify the effect of a bend on the DNA plug motion. In a branching system, a simple kinematic relationship was discovered relating the quantity of DNA in each downstream branch to its relative channel cross-sectional area.

High-throughput fabrication of sub-micron pillar arrays for free-solution DNA electrophoresis without E-beam lithography

A new technology approach for the design, fabrication and application of an integrated free-solution electrophoresis microsystem is presented. The technology approach, which utilizes the dual-photolithography provided from a stepper and a contact aligner, allows fast and flexible formation of sub-micron pillar array patterns on a silicon substrate. Combining with standard microfabrication technique and deep-reactive-ion-etching (DRIE), very high aspect-ratio sub-micron pillar arrays can be integrated in regular microfluidic system for free-solution DNA electrophoresis. DNA interaction with pillars inside the microsystem has been demonstrated, supporting the new technology approach a novel technique for Si-based free-solution electrophoresis microsystem fabrication

Glass-Silicon Bonding Technology with Feed-Through Electrodes for Micro Capillary Electrophoresis

A new technology approach for the design, fabrication and application of a novel integrated microsystem for micro-capillary electrophoresis is presented. The technology approach, using amorphous-silicon-assisted glass-to-silicon anodic bonding, allows the integration of feed-through electrodes formed over a thick insulating layer. In spite of the thick insulating layer and non-uniform topography, hermetic and strong bonding can be achieved due to the contribution of α-silicon during the bonding. Electrophoresis experiments have been performed in the fabricated devices, and the transport of DNA fragments has been demonstrated. The generation of gas bubbles due to electrolysis, which can interfere with the electrophoresis process, and potential solutions are discussed.

Nonlinear Electrophoretic Mobility of Large DNA Molecules in Microsystems with Sub-Micron Pillar Arrays

This paper presents a systematic study of free-solution electrophoretic motion of large DNA molecules in microsystems integrated with sub-micron pillar arrays. A nonlinear dependence of the DNA electrophoretic mobility on the applied electric field is observed. The interaction between DNA molecules and the pillar arrays is inspected under high optical magnification. Several distinct DNA molecular motions at different electric fields, associated with the DNA nonlinear response, are identified. The measured free-solution DNA mobility, inside the pillar arrays, has been found to be within the prediction range based on the Biased Reptation with Fluctuations Model.