Integrations of advanced functional materials and devices for microfluidic applications

In realizing the full potential of lab-on-a-chip devices, it is necessary to integrate various functional components into the system. In this thesis, different types of advanced functional materials and devices are coupled into microfluidic systems to explore functional components.;By combining with hydrodynamics in microfluidic system, micromixer, microvalve and micropump were realized. An effective planar passive micromixer with relatively simple construction was developed based on chaotic velocity distribution in microchannels. On the other hand, a unique bubble generation technique has been developed and applied as micro-valve and micro-pump 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. Integrations of quartz crystal microbalance and lead magnesium niobate-lead titanate (PMN-PT) single crystal resonators show the sensitive and label-free capabilities of the piezoelectric sensing in microfluidic system. Flow rates, viscosity and mass accumulations can be well detected by these systems from observing the resonant frequency shift. Such kind of microfluidic system was further developed by modifying the surface with a nickel pillar array to introduce active magnetic force control for the piezoelectric sensor. The chip was succeeded in trapping and detecting target cancer cells.;Graphene was introduced into microfluidic system for the first time. 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 exhibits the advantage of low 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.