Controlled multiphase interfaces in microfluidic systems for chemical/biological sensing

Multiphase interfaces, which are scale-dependant, play an important role in microfluidics to develop a broad range of applications. There are rising demands for interface control methods, which provide more precise control over the positions and the configurations of the interfaces, consume minimum or zero power, possess simple structures, and require fewer fabrication steps. In my studies, I explored the controlled interfaces in microfluidic systems to provide competitive alternatives in the development of chemical/biological sensors and devices.;In Chapter 2, selective alkanethiol treatment on gold or copper surfaces is used to create hydrophilic-hydrophobic boundaries at the boundaries between glass and these metal surfaces in microfluidic channels. Robust liquid-air interfaces, featured with different 3-D structures, are formed at these boundaries. This method has been further extended into the application of liquid crystal for aqueous phase sensing in a microfluidic channel structure, which is described in Chapter 5.;In Chapter 3, an interface of liquid crystal for vapor phase sensing application is stabilized using a micropillar array structure, which provided an effective tool for utilizing liquid crystal interface for sensing. The sensing performance was improved by better design and process optimization. In Chapter 4, a sensing interface between liquid crystal and the target aqueous phase is created using the laminar flow of the liquids within a packaged microfluidic sensing device. This study provided an autonomous sensing scheme, which can be used without technical personnel evolved, and contributed to fulfilling the demand of conducting sensing application in the hostile environments inaccessible to human beings. In Chapter 6, I describe a bubble control device for microfluidic systems, which harnesses the controlled liquid-air interfaces for bubble trapping and removal. This study provided a solution for the long-existing problem of inadvertently introduced and unwanted bubbles in the microfluidic networks, which could negatively and significantly affect the performance of the device as well as the experiment results. The study of cylindrical interfaces was extended and interface between different liquids were realized with potential applications in biological research, bio/chemical sensing, etc. This new extended study is presented in Chapter 7.