An open microfluidic device based on thermocapillary actuation: Design, fabrication and sensor integration

Miniaturized automated systems for liquid routing, mixing, and analysis are expanding diagnostic capabilities in medicine, genomic research, environmental monitoring and biodefense. Within this field of research, a new approach to fluidic actuation based upon the modulation of liquid surface tension has emerged in which discrete droplets are transported in open channel architectures. This thesis focuses on the development of one such actuation technique known as thermocapillary flow where time-varying spatial temperature distributions are used to manipulate nanoliter liquid samples.; Using the thermocapillary microfluidic device presented herein, thin-film micro-heater arrays are programmed to generate temperature fields which modify liquid surface tension, thereby providing electronic control over the direction, timing and flow of droplets along lithographically defined liquophilic pathways. Droplets are induced to move, split, merge, and dispense from adjacent reservoirs using low operating power between 20 and 150 mW.; A quantitative analysis of the dispensing process is performed in which thermocapillary forces regulate rivulet length and split droplets off liquid emerging from a reservoir. The minimum power necessary for the droplet formation process is determined as a function of both reservoir volume and channel width. Static and time-dependent hydrodynamic simulations provide an estimate of resulting droplet volumes.; Droplet detection, liquid thickness measurements and liquid differentiation are achieved via indirect evaluation of transient microheater thermal profiles. Analytical and numerical simulations show the effect of liquid density and heat capacity on thermal rise times. Numerical models also indicate that an increase in liquid volume to surface area ratio will decrease the resolution with which one can measure droplet thickness.; A non-intrusive optical method for microfluidic analysis is demonstrated based on evanescent wave sensing. SiNx waveguides integrated with the thermocapillary actuation device are used to monitor solution concentration and enzyme reaction rates of droplets transported on the waveguide surface. Numerical models of the liquid/waveguide system are evaluated to investigate droplet induced scattering effects.