MEMS Interfaces for Bioanalysis Systems

Abstract: This thesis deals with various aspects of using open microfluidic interfaces. Three specific areas of application are studied.The first is air-to-liquid interfacing in biosensors with possibilities for component inte­gration. A micromachined interface for airborne sample-to-liquid and droplet-to-liquid adsorption is discussed. It enables a robust sheet liquid flow serving as adsorption site. The inter­face properties are presented. Along with the interface, a novel method and system for rapid detection of dust and vapour-based narcotics and explosives traces is introduced. The QCM sensor detection principle with antibody immunoassay is described. Having shown the working principles of molecular adsorption to liquid surface and molecular detection with QCM technology, an integrated device is introduced. Diffusion as an effective transport mechanism in this microfluidic device is discussed. By holding the two components (inter­face and QCM) together with a double-sided adhesive, anisotropically vertically conductive tape, we achieve three functions, namely fixation, electrical connection and liquid sealing. Finally, enhanced electrostatic trapping of small particles to the liquid interface is demon­strated.The second area concerns open microfluidics for the integration of capillary electropho­resis and mass spectroscopy. A technique for hyphenation between CE and MALDI-MS is presented. Two closed fused-silica capillaries were connected via a silicon chip comprising an open microcanal. The influence of the capillary-to-microcanal connection is discussed, as well as a simple technique to control evaporation from the open microcanal.The third area concerns microfluidics enabling studies of single cells in asymmetric en­vironments. Using extracellular matrix or synthetic gel-embedding cells in an assay chamber, cells thrive and proliferate. This makes it possible to carry out medium to long term cultiva­tion of cells in a more physiological, controlled 3D environment than in traditional 2D cul­tures. The gels are discussed in terms of handling as well as their properties. A gel and micro­fluidic device for three dimensional cell culture with microgradient environments is pre­sented. Finally, a method for studying cilia-forming cells in asymmetric microfluidic environments is presented. Bending the primary cilium with a fluid flow will give rise to a response, but sensitivity to flow direction has only been sparsely studied. Design considerations are presented and discussed.

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