Author: Zhang, Kai
Title: Integrations of advanced functional materials and devices for microfluidic applications
Degree: Ph.D.
Year: 2011
Subject: Microfluidics
Microfluidic devices
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xxiv, 173 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: Microfluidic systems promise reducing laboratory operations in miniaturized chips, which are featured with reduced reagent consumption and shorter analysis time. In realizing the full potential of these lab-on-a-chip devices, it is necessary to integrate various functional components into the system, like: sample prehandling, manipulation, and detection. However, the complex interface between fluid networks and external (electric, thermal, optical, etc.) components limits the full development of microfluidic functions and leaves great space for integrations. In this thesis, a series of advanced functional materials and devices are coupled into microfluidic systems to explore functional components. By combining with dynamic fluid flow design and laser induced thermal bubble technique, micromixer, microvalve and micropump were realized in microfluidic chips. An effective planar passive micromixer with relatively simple construction was developed based on chaotic velocity distribution in microchannels. Experimental results show that, for these two flows with a wide range of flow rates, good mixing uniformity with high mixing efficiency were obtained. On the other hand, a unique bubble generation technique has been developed and applied as micro-valve and micro-pump in microfluidic system by utilizing laser-induced heat. It was demonstrated in the experiments that, efficient generation of thermal bubbles with controllable sizes can be achieved using different geometries of chromium pads immersed in various types of fluids. Effective blocking of microfluidic channel and direct pumping of the fluid with selectable directions have also been demonstrated, respectively.
To develop alternative bioassay components, various piezoelectric sensors have been integrated into microfluidic systems for in-situ dynamic fluid properties monitoring and chemical and biological analysis. A microfluidic system with acoustic wave sensor employing quartz crystal microbalance embedded in the microfluidic channel was developed by soft lithography technique and characterized by measuring resonance frequency of the sensor under different service conditions. Detections of dynamic fluids in various concentrations and flow rates showed that shift of resonant frequency was observed when there was variation in mass or viscosity of the fluid passing through the microchannels. Such kind of microfluidic system was further developed by modifying the surface of quartz crystal microbalance with a nickel pillar array to introduce active magnetic force control for the piezoelectric sensor. The functionalities of the system were tested by trapping suspended superparamagnetic micro-beads (SPMBs) in fluids onto the nickel pillar array with a manually controlled magnetic field and by detecting the accumulated mass from the resonant characterization of the piezoelectric sensor at the same time. Resorting to surface functionalized SPMBs, the microfluidic system then succeeded in trapping and detecting target cancer cells. After that, similar techniques were utilized to develop microfluidic devices integrated with lead magnesium niobate-lead titanate (PMN-PT) single crystal-based piezoelectric resonators. Finally, the potentials of graphene to be used as a functional material for surface modification of microfluidic channels and in fluid-gated field effect transistors (FETs) were studied. Hydrodynamic property of graphene was analyzed with the fabricated graphene-modified microchannels. Results show that the wetting property dominates the hydrodynamic behavior rather than the nanotribological characteristics for graphene sheet. Furthermore, a novel graphene FET based on fluid gate was developed and analyzed. The transistor behaves similar ambipolar characteristics as conventional back-gated transistors while owns the advantage of lower power consumption. Experimental results also demonstrated the fact that threshold voltage and output current of the graphene FETs can be tuned accordingly by the wetting property and electrical double layer of the top fluid gates.
Rights: All rights reserved
Access: open access

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