Droplet- and Bead-Based Microfluidic Technologies for Rheological and Biochemical Analysis.

摘要

The development of microfluidics in recent decades has opened new methods for chemical, physical, and biomedical analysis. Two particularly exciting possibilities are portable, self-contained analysis systems and high-throughput, multiplexed analysis systems. While earlier systems have been based on continuous-flow microfluidics, the advantages of droplet-based microfluidics, with droplets of one liquid phase surrounded and isolated by a continuous immiscible second liquid phase, are becoming apparent. However, many of the analysis tools which exist for continuous phase microfluidics are lacking in the droplet regime. This dissertation describes the development of tools for analysis of rheological properties of nanoliter-volume (20 to 30 nL) microfluidic droplets. We report measurements of viscosity and viscoelastic phase angle. Viscosity measurements are achieved by observing the motion of a droplet through a contraction in the channel and relating the pressure, flow rate, and geometric parameters to the viscosity with the Hagen-Poiseuille equation. Phase angle is measured by applying an oscillatory pressure to a droplet located in a contraction and comparing the applied pressure to the droplet interface response. At low frequencies, where the elasticity of the interface is expected to dominate, droplets behave similarly regardless of polymer concentration. As the frequency increases, to a maximum of 6 Hz (~37 rad/s), the elastic contribution of the droplet fluid becomes apparent and samples can be distinguished. In addition, a simple, single mask method for fabricating microstructures with smooth 3D gradients and arbitrary shape in SU-8 and polydimethylsiloxane (PDMS) is presented. Demonstration applications are shown, involving particle organization, particle imaging, and size-based particle sorting. Alone or in combination with droplet-based approaches, particle-based microfluidic assays offer potential for high-throughput and multiplexed assays. This fabrication technique makes accessible different methods for particle-based assays, especially for presentation of results. This dissertation also presents preliminary work toward a micro-scale dielectric barrier discharge plasma-based electronic pressure actuator, for control of microfluidic flows. Finally, there is discussion of the distributed health diagnostics design, in particular for microfluidic technologies, through the lens of technology assessment. This highlights the importance of interacting with users and considering the broader factors of governments, regulations, infrastructure, economics, climate, geography, culture, and religion.