Browsing by Subject "Microfluidics."

Now showing 1 - 4 of 4

Open Access
Injection molding of polymeric microfluidic devices
(2013) Koska, Arif Koray
Mass-production of microfluidic devices is important for fields in which disposable devices are widely used such as clinical diagnostic and biotechnology. Injection molding is a well-known, promising process for the production of devices on a mass-scale at low-cost. The major objective of this study is to develop a technique for repeatable, productive and accurate fabrication of integrated microfluidic devices on a mass production scale. To achieve this, injection molding process is adapted for the fabrication of a microfluidic device with a single microchannel. During the design procedure, numerical experimentation was performed using Moldflow® simulation tool. To increase the product quality, high-precision mechanical machining is utilized for the manufacturing of the mold of the microfluidic device. A conventional injection molding machine is implemented for the injection molding process of the microfluidic device. Injection molding is performed at different mold temperatures. The warpage of the injected pieces is characterized by measuring the part deformation. The effect of the mold temperature on the quality of the final device is assessed in terms of part deformation and the bonding quality. From the experimental results, one-to-one correspondence between the warpage and the bonding quality of the molded pieces is observed. As the warpage of the pieces decresases, the bonding quality increases. A maximum point for the breaking pressure of the bonding and the minimum point for the warpage was found at the same mold temperature. This mold temperature was named as the optimum temperature for designed microfluidic device. The experimental results are also used to discuss the assessment of the simulation results. It was observed that although Moldflow® can predict many aspects of the process, all the physics of the injection molding process cannot be covered.
Open Access
Microfluidic based differential electrochemical sensors
(2013) Akay, Özge
Lab-on-a-chip systems aim to integrate analytical techniques on a single chip to achieve high-throughput measurements with little reagent. Microfluidic devices use the advantage of fluid dynamics in microscale to generate new physical phenomena which are less familiar in macroscale. Laminar flow is one of these emergent phenomena in microscale dimensions. Fluids flowing in a microchannel with low Reynolds number (Re), have small inertial effects which suppress the turbulent mixing. Ability to control liquids without turbulent mixing provides new tools for integration of analytical techniques on a single chip. In this work we present a new type of electrochemical device based on hydrodynamic modulation in a microfluidic channel. The presented microfluidic device is a kind of hydrodynamic modulation voltammetry (µ-HMV) that uses a periodic modulation of two laminar streams of buffer and analyte solutions in a micro channel. The periodic modulation of the laminar flow generates periodic variation of mass transport to the electrode surface. The generated periodic electrochemical current is detected by a phase-sensitive detector. The differential electrochemical sensor eliminates charging and other transient background current and provides high sensitivity with a detection limit of 10 nM. This technique provides a convenient hydrodynamic electrochemical detection with a relatively simple and compact instrument which does not require any moving mechanical parts.
Open Access
Microfluidic device with 3D electrode structure for high throughput dielectrophoretic applications
(2014-10) Zeinali, Soheila
Microfluidics is the combination of micro/nano fabrication techniques together with knowledge of fluid behavior at the microscopic level to pursue powerful techniques in controlling, manipulating and measuring chemical, physical and biological processes at micro/nano scale. Sorting and separation of bio-particles are highly considered in diagnostics and biological analyses. By implementing the characteristics of microscale flow phenomenon, dielectrophoresis (DEP) has offered unique advantages for microfluidic devices. In DEP devices asymmetric pair of planar or three dimensional (3D) electrodes could be employed to generate non-uniform electric field. In DEP applications, facing 3D sidewall electrodes is considered to be the key solution of increasing device throughput because of producing homogeneous electric fields along the height of microchannels. Despite all advantages, fabrication of 3D vertical electrodes requires considerable challenge. In this thesis, in order to highlight the advantage of 3D electrodes over planar electrodes, the simulations are performed. Based on the developed computational model, the design parameters are decided. For the fabrication of the device, two different fabrication techniques have been proposed. In the first method, both the mold and the electrodes are fabricated using high precision machining. In the second method, the mold is fabricated with tilted sidewalls using high precision machining and the electrodes are deposited on the sidewall using sputtering together with a shadow mask fabricated using wire electric discharge machining (WEDM). The both techniques are assessed as highly repeatable and robust methods. Only the manipulation of particles with negative-DEP has been demonstrated in the experiments, and the throughput values up to 105 particles/min have been reached in a continuous flow.
Open Access
Microfluidics for plasmonic sensors
(2009) Ertaş, Yavuz Nuri
In this thesis, we integrate microfluidics with grating-coupled surface plasmon configurations for sensing applications. First, in order to observe optimal excitations, we introduce procedures for modification of the surface profiles of gratings acquired from commercially available optical storage disks. A must requirement in plasmonic systems, thin film metal deposition is performed. Soft lithographic techniques are applied to coated disks to transfer the surface topography of the disks to an elastomeric material, PDMS. Optical lithography is used to fabricate microfluidic channels to where fluid will be injected. After fabricating the final structure, ellipsometric measurement is used to investigate the device performance. Experimental results were in consistence with the theoretical simulations providing similar behaviours of reflection spectra. The resonance wavelengths are found to be occuring very near to the expected values along with high quality factors. However, to the device structure, an intensity loss is observed which can be further improved. We achieved the tuning of the resonance wavelength by changing the refractive index of the medium inside the microchannel. Integration of the microfluidic channel to surface plasmon studies may open up many applications such as biomolecular sensing.