Microfluidic devices for droplet sorting, on-line sensing, and microwiner

Microfluidics is a promising technology that involves microsystem engineering, physics, materials, chemistry, and biotechnology. Microfluidic devices have many advantages such as small liquid volume and energy consumption, fast reaction, and good throughput of assays.;The first study of this thesis is focused on the development of a microfluidic droplet sorter able to select micro-droplet-based biochemical reactors based on their optical properties. The sorting is accomplished utilizing two bilayer pneumatic micro-valves as sorting controllers. This micro-valve, consisting of a liquid flow channel in the bottom layer, an air flow channel in the upper layer, and a flexible thin membrane in the middle layer, is a widely used building block for many large-scale integrated microfluidic systems. Rapid deflation of a pressurized micro-valve generates a fluidic pressure exerted at an optically targeted micro-droplet. This, in turn, diverts the droplet into one of multiple outlet channels. This sorter is advantageous over others by having a reduced interference to biological species or microorganisms encapsulated inside droplets and facilitating easy integration of a sorting function into large-scale microfluidic systems.;The second study aims at developing a microfluidic sensing device for improving efficiency of online concentration measurement in liquid solutions. The device integrates multiple electrical impedance-based sensors and a microfluidic concentration gradient generator onto a low-cost printed circuit board platform, to achieve a cost-effective microsystem solution. This device allows acquiring sufficient measurement data at a high concentration resolution that is generally required to create complex impedance-to-concentration mapping relationships for analyzing a multi-composition liquid solution. The Principle Component Analysis method is employed to analyze the measured data and reduce the data complexity from three to two dimensions. This further allows differentiating and quantifying unknown concentrations of multiple compositions in a liquid sample.;The third study involves a novel continuous flow micro-winery with a great potential to rapidly screen important parameters involved in making quality wines such as types of juice and yeast, and fermentation temperature and light conditions. This microsystem technology advances the winemaking area by reducing the fermentation time from 1-2 weeks to 1-3 days and eliminating the operation of separating wine product from yeast cells. In the device, a hydrophilic porous membrane separates a serpentine juice flow channel from a yeast storage chamber, at which yeast cells are immobilized and fermentation takes place; a hydrophobic porous membrane is additionally placed on the bottom of yeast chamber to allow escaping CO2 from the device. The immobilized yeasts, exposed to a continuous juice flow, have a higher juice-to-wine conversion rate and thus an increased fermentation efficiency.;In conclusion, this research has advanced the microfluidics area with a novel micro-droplet sorter, an online concentration measurement device, and an unprecedented microscale winery chip.