A miniaturized (bio)chemistry lab to perform an entire sample analysis of small liquid, bioliquid, medical samples on the chip scale, named bioMEMS (microelectromechanical systems), Lab-on-a-Chip (LOC) or muTAS (micro total analysis systems), is an important emerging technology. Two key components are droplet actuation and liquid phase chemical sensing. In this work, we study both components.; This dissertation discusses the first systematic study of thermocapillary droplet actuation on chemically homogeneous and striated surfaces. We developed a model surface on a silicon substrate which allows us to use a conveniently small thermal gradient to drive the droplet. Based on the experimental results, we concluded that a droplet experiences a pinning force during droplet demobilization; when the driving force is larger than this pinning force, the droplet travels at a speed proportional to the product of droplet size and thermocapillary stress. This pinning force can be formulated based on liquid properties and contact angle hysteresis, i.e., the difference of contact angles between the advancing and receding ends.; In the aspect of liquid phase chemical sensing, two label-free liquid sensing techniques, capacitive sensing and quantum cascade laser evanescent-wave sensing, were developed in this thesis. A two-inverter oscillating circuit was employed to sense the droplet volume, chemical composition, and the location of the droplet on the digital thermocapillary device fabricated on glass substrate. Design guidelines of capacitive sensing electrodes have been developed specially for these devices. Evanescent-wave droplet sensing was implemented with a silver halide fiber protruding through the droplet as the evanescent-wave sensing element with mid-infrared quantum cascade lasers as the light sources. The mid-infrared evanescent wave directly excites the vibrational transitions inside the liquid, and thus enables label-free liquid sensing.; Efficient cooling of quantum cascade lasers is a central issue for the stability of the output power, which is of importance when using quantum cascade lasers as the light sources for optical sensing. The final section of this thesis discusses direct liquid cooling of quantum cascade lasers. A refrigerant liquid cools the quantum cascade laser from the top surface of the laser ridge, providing convective cooling in addition to conductive cooling through the laser substrate. Cooling effects with different types of liquids, liquid flow, and cooling modes are presented.
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