Yun-Ju Chuang

Microfluidic Systems for Biosensing

In the past two decades, Micro Fluidic Systems (MFS) have emerged as a powerful tool for biosensing, particularly in enriching and purifying molecules and cells in biological samples. Compared with conventional sensing techniques, distinctive advantages of using MFS for biomedicine include ultra-high sensitivity, higher throughput, in-situ monitoring and lower cost. This review aims to summarize the recent advancements in two major types of micro fluidic systems, continuous and discrete MFS, as well as their biomedical applications. The state-of-the-art of active and passive mechanisms of fluid manipulation for mixing, separation, purification and concentration will also be elaborated. Future trends of using MFS in detection at molecular or cellular level, especially in stem cell therapy, tissue engineering and regenerative medicine, are also prospected.

A novel fabrication method of embedded micro channels employing simple UV dosage control and antireflection coating

This paper proposes a novel method to fabricate multi-layers of embedded micro fluidic structures by simply employing time-controlled UV exposure on thick SU-8 resist and an anti-reflection coating on the bottom surface to eliminate the reflection light induced exposure. Test results show that the top wall thickness of embedded channels can be well controlled to a resolution of 2 /spl mu/m for a UV dose of 120-190 mJ/cm/sup 2/. Stacked channels have also been successfully fabricated and show no interference on the bottom structures when exposing the top structures. This simple and inexpensive method can be applied to fabricate multi-layers of complex fluidic systems, for applications such as /spl mu/TAS, inkjet printheads, capillary electrophoresis, and micro PCR.

Self-masked high-aspect-ratio polymer nanopillars

In this paper, a simple, cost effective, and potentially universal method is proposed for the formation of high-aspect-ratio nanopillars on various polymers. Our method involves direct reactive ion etching (RIE) using self-formed nanomasks oriented from a dummy material (cover glass). The mechanism is evaluated using nanopillar characterization and surface analysis results from x-ray photoelectron microscopy (XPS) and Auger electron microscopy (AES). By varying the dummy material configuration and modifying the RIE etching time, the distribution and dimensions of the nanopillars can be manipulated to meet a range of requirements. The maximum structural aspect ratio of 60 (6.7 microm high and 112 nm thick nanopillars) can be easily prepared using a 60 min self-masked high-aspect-ratio polymer nanopillars fabrication (SMHAR) process on poly(monochloro-p-xylylene) (Parylene C). Furthermore, nanopillars can also be generated using the same SMHAR process on poly(dimethylsiloxane) (PDMS) and SU-8 photoresist, creating nanostructured PDMS or SU-8 materials in lab-on-a-chip (LOC) or nano/micro-electromechanical systems (N/MEMS).

Dynamics of hydrogen nanobubbles in KLH protein solution studied with in situ wet-TEM

Although the stability of the nanobubble remains a controversial issue that is subject to the classical predictions of high Laplace pressure, we demonstrate that a hydrogen nanobubble can be generated and stabilized in an aqueous solution of Keyhole limpet hemocyanin (KLH) protein via an electron radiolysis process. The hydrogen gas inside the nanobubble is in a “dense gas” phase that is characterized by a Knudsen number and number density of hydrogen molecules. The dynamics of nanobubbles are analyzed using time-series electron microscopy images. The growth of small nanobubbles will be affected by the largest neighboring nanobubble; however, a diffusive shielding effect for small nanobubbles is observed. Locally, anti-Ostwald ripening of nanobubbles can be observed; however, the global growth behavior among the nanobubbles is randomly correlated because the characteristic diffusion length of the hydrogen molecules is considerably greater than the average spacing among the nanobubbles.

A Wettability Switchable Surface Driven by Electrostatic Induced Surface Morphology Change Without Energy Interference On Reagents in Droplets

A novel surface wettability switchable device was successfully demonstrated by changing the surface morphology to induce contact angle change. The surface morphology transformation carried out from the deflection of thin PDMS membrane, driven by electrostatic force, can dynamically change the surface contact angle from 131 ° to 152 ° based on the contact area variation. The electrostatic energy can be throughout shielded out from droplets thanks to ground shielding effect. Since there is no direct physical or chemical (thermal, electrical, UV light etc.) interference from this actuation mean to biological solutions, the proposed method has great potential on microscale droplet transportation and is suitable to many applications especially digital fluidic systems.

Self-Formed High-Aspect-Ratio Polymer Nanopillars by RIE

In this work, a novel fabrication process of self-formed polymer nanopillars by reactive ion etching (RIE) is proposed. During this one-step RIE process, polymer nanopillars were generated adjacent XPS surface analysisto glass slide that was partially covered on treated polymer of either PDMS or parylene C. The surface morphologies and water contact angles were compared for different RIE parameters of RF-power and etching time. The aspect-ratio and water contact angle of nanopillar could reach 10 and 162.6deg, respectively. Furthermore, the mechanism of this novel fabrication process was established based on the evidences of nanopillar distribution and XPS surface analysis.

A thermal droplet generator with monolithic photopolymer nozzle plate

A monolithic thermal droplet generator with photopolymer nozzle plate has been developed and demonstrated to operate successfully. The micro droplet generators are realized by direct formation of the nozzles plate, made by SU-8 photoresist, on the top of a silicon wafer with a micro heater array. For the monolithic fabrication, a UV-dosage control and antireflection coating techniques are used to form chambers, manifolds and nozzles. This simpler and more cost-effective fabrication process can lower the fabrication complexity as well as cost, and achieve high alignment accuracy on the nozzle plate to the heater.

The Preparation of Self-formed PDMS Nanostructures by RIE Etching

In this study, a novel fabrication method of nanostructure by reactive ion etching (RIE) process on PDMS without predefinition of nanopattern is proposed. During etching process, self-formed high-aspect-ratio nanostructure was observed on PDMS surface adjacent to SiO2 area, suggested the provision of nano masks from the SiO2 residue during RIE etching. In tuning the flow rate of working gases (CF4, O2), the distribution of nanostructure can be controlled. Furthermore, it was observed that different species of nanostructures could be fabricated by the selection of mask materials (SiO2, Cu) under RIE etching.

Fabrication and Characterization of a High-Performance Multi-Annular Backscattered Electron Detector for Desktop SEM

Scanning electron microscopy has been developed for topographic analysis at the nanometer scale. Herein, we present a silicon p-n diode with multi-annular configuration to detect backscattering electrons (BSE) in a homemade desktop scanning electron microscope (SEM). The multi-annular configuration enables the enhancement of the topography contrast of 82.11 nA/μm as compared with the commercial multi-fan-shaped BSE detector of 40.08 nA/μm. Additionally, we integrated it with lateral p-n junction processing and aluminum grid structure to increase the sensitivity and efficiency of the multi-annular BSE detector that gives higher sensitivity of atomic number contrast and better surface topography contrast of BSE images for low-energy detection. The responsivity data also shows that MA-AL and MA p-n detectors have higher gain value than the MA detector does. The standard deviation of measurements is no higher than 1%. These results verify that MA p-n and MA-AL detectors are stable and can function well in SEM for low-energy applications. It is demonstrated that the multi-annular (MA) detectors are well suited for imaging in SEM systems.