Yi Je Juang

Design and fabrication of CD-like microfluidic platforms for diagnostics: Polymer-based microfabrication

Several microfabrication methods for polymer-based CD microfluidic platforms are presented in this paper. For prototyping, both traditional CNC-machining and photolithography techniques were used. For mass production, mold inserts were made by CNC-machining of tool steel and LIGA-like processes such as UV photolithography, photolithography/electroplating, and photolithography/deep reactive ion etching (DRIE). Several molding methods were tried, including liquid resin casting, thin wall injection molding, and hot embossing. Advantages and disadvantages of each method are explained. Plastic bonding for microfluidic platforms is also briefly discussed.

Long-range and superfast trapping of DNA molecules in an ac electrokinetic funnel

In this work we report a microfluidic platform capable of trapping and concentrating a trace amount of DNA molecules efficiently. Our strategy invokes nonlinear electro-osmotic flow induced by charge polarization under high-frequency ac fields. With the asymmetric quadrupole electrode design, a unique converging flow structure can be created for generating focusing effects on DNA molecules. This focusing in turn transforms into a robust funnel that can collect DNA molecules distantly from the bulk and pack them into a compact cone with the aid of short-range dipole-induced self-attraction and dielectrophoresis. Our results reveal that not only can DNA molecules be concentrated within just a few seconds, but also they can be focused into threads of 1 mm in length, demonstrating the superfast and long-range trapping capability of this funnel. In addition, pico M DNA solutions can be concentrated with several decades of enhancement without any continuous feeding. Alternating concentration and release of DNA molecules is also illustrated, which has potentials in concentrating and transporting biomolecules in a continuous fashion using microdevices.

Black silicon SERS substrate: Effect of surface morphology on SERS detection and application of single algal cell analysis

In this study, we have investigated the effect of the surface morphology of the black silicon substrate on surface enhanced Raman spectroscopy (SERS) and explored its application of single algal cell detection. By adjusting the O2 and SF6 flow rates in the cryogenic plasma etching process, different surface morphologies of the black silicon substrate was produced without performing the lithographic process. It was found the Raman signals were better enhanced as the tip density of the black silicon substrate increased. In addition, as the thickness of the deposited gold layer increased, the SERS effect increased as well, which could be owing to the generation of more hot spots by bridging individual silicon tips through deposition of gold layer. For the black silicon substrate with tip density of 30 tips/μm(2) and covered by 400 nm deposited gold layer, the detection limit of 10 fM R6G solution concentration with uniform SERS effect across the substrate was achieved. Furthermore, detection of individual algal cell (Chlorella vulgaris) was performed at the SERS substrate as fabricated and the Raman signals of carotenoid and lipid were substantially enhanced.

Microfluidic Enzyme-Linked Immunosorbent Assay Technology

In this chapter, we have presented an overview of microfluidic enzyme-linked immunosorbent assay (ELISA) by first introducing the principle of immunoassay, ELISA, and microfabricated devices, followed by a discussion of microfabrication technology and the characterization of microfluidic components. Significant advances in laboratory technology are contributing to the further understanding of microfluidic function, surface modification and immobilization, which lead to the development of improved biomolecule detection methods and prospective applications. For the future, the exploitation of more robust-manufacturing processes and integrated assay systems in an automatic fashion with much reduced assay time and reagent consumption will allow for the effective detection and quantification of biological agents that are of interest in medical diagnostics, food safety surveillance, and environmental monitoring.

Packaging of microfluidic chips via interstitial bonding technique

In this paper, we describe an interstitial bonding technique for packaging of microfluidic chips. The cover plate is first placed on top of the microfluidic chip, followed by dispensing the UV‐curable resin into the resin‐loading reservoirs. With the interstitial space between the cover plate and the microfluidic chip connecting to the loading reservoirs, the UV‐curable resin wicks through capillary force action and hydrostatic pressure generated by the liquid level in the resin‐loading reservoirs. When reaching the microchannels, the UV‐curable resin stops flowing into the microchannels due to the force balance between the surface tension and hydrostatic pressure. The assembly is then placed under the UV light, followed by further curing in the thermal oven. It is found that there is no leakage from the bonded microfluidic chips and a good DNA separation result was obtained by using the microfluidic chips as fabricated. This bonding technique is relatively simple and fast, which can be applied to the packaging of microfluidic chips made from hybrid materials with complicated designs as long as the interstitial space connects to the loading reservoirs.

Separation of microalgae with different lipid contents by dielectrophoresis

In this study, the effect of the solution conductivity on the behavior of microalgal cells (Chlorella) with different lipid contents under a non-uniform electric field was investigated. It was found that, for the algal cells with 11 wt% lipid content, the crossover frequency is between 2 and 10 MHz when the solution conductivity is within 1.4 and 2.95 mS/cm, and increases as the solution conductivity increases. As to the microalgal cells with 45 wt% lipid content, they experienced negative DEP at frequency below 20 MHz when the solution conductivity is within 2.06 and 2.95 mS/cm. However, positive DEP was observed when the solution conductivity becomes 1.4 mS/cm. In a mixture of the algal cells, those with different lipid contents were successfully separated by DEP at solution conductivity of 2.95 mS/cm and frequency of 20 MHz.

Electrokinetic trapping and surface enhanced Raman scattering detection of biomolecules using optofluidic device integrated with a microneedles array

In this study, microneedles which possess sharp tips were utilized to trap and detect the biomolecules. Owing to the large curvature, the tips of the microneedles created a substantially high gradient of electric field under the non-uniform electric field which served as not only the trapping sites but also the substrate for surface enhanced Raman scattering (SERS). Separation of polystyrene microparticles with different sizes and two kinds of biomolecules (Staphylococcus aureus (S. aureus) and the red blood cells (RBCs)) were demonstrated. Moreover, in situ detection of S. aureus was performed immediately after separation was completed. The results showed that, after 15 s of sample collection, the Raman signals of S. aureus were detected and greatly enhanced through SERS effect.

Applications of microfluidics in microalgae biotechnology: A review

Microalgae have been one of the important sources for biofuel production owing to their competitive advantages such as no need to tap into the global food supply chain, higher energy density, and absorbing carbon dioxide to mitigate global warming. One of the key factors to ensure successful biofuel production is that it requires not only bioprospecting of the microalgae with high lipid content, high growth rate and tolerance to environmental parameters but also on‐site monitoring of the cultivation process and optimization of the culturing conditions. However, as the conventional techniques usually involve in complicated procedures, or are time‐consuming or labor intensive, microfluidics technology offers an attractive alternative to resolve these issues. In this review, applications of microfluidics to bioprospecting in microalgae biotechnology were discussed such as cell identification, cell sorting/screening, cell culturing and cell disruption. In addition, utilization of microalgae in micro‐sized fuel cells and microfluidic platforms for biosensing was addressed. This review reports the recent studies and offers a look into how microfluidics is exploited to tackle the issues encountered in the microalgae biotechnology.

Development of flow through dielectrophoresis microfluidic chips for biofuel production: Sorting and detection of microalgae with different lipid contents

In this study, a continuous flow dielectrophoresis (DEP) microfluidic chip was fabricated and utilized to sort out the microalgae (C. vulgaris) with different lipid contents. The proposed separation scheme is to allow that the microalgae with different lipid contents experience different negative or no DEP force at the separation electrode pair under the pressure-driven flow. The microalgae that experience stronger negative DEP will be directed to the side channel while those experience less negative or no DEP force will pass through the separation electrode pair to remain in the main channel. It was found that the higher the lipid content inside the microalgae, the higher the crossover frequency. Separation of the microalgae with 13% and 21% lipid contents, and 24% and 30%-35% lipid contents was achieved at the operating frequency 7 MHz, and 10 MHz, respectively. Moreover, separation can be further verified by measurement of the fluorescence intensity of the neutral lipid inside the sorted algal cells.

Fabrication of long poly(dimethyl siloxane) nanochannels by replicating protein deposit from confined solution evaporation

A relatively simple, inexpensive and reliable technique was developed to fabricate an array of nanochannels. Moreover, the nanochannels are directly integrated to microchannels as a whole, which facilitates solution loading from the millimeter-scaled loading reservoirs into the nanochannels. It is found that continuous bovine serum albumin (BSA) line structures with triangle-like cross section at nanoscale can be obtained by evaporation of BSA solution with concentration between 0.5 wt. % and 1 wt. % inside the microchannels. The poly(dimethyl siloxane) nanochannels were replicated from these line structures, followed by sealing with the glass slide. The DNA molecules can be stretched inside the nanochannels as fabricated.