Abstract: A device for real time monitoring of fluid composition in microfluidic devices. The invention can be integrated into any microfluidic device where fluid moves along a pathway with a measurement region consisting of at least two measurement electrodes. The fluidic pathway can contain an unbound droplet, a droplet confined in at least one aspect, or a continuous flow. The device also includes control circuitry connected to measurement electrodes that allows for the determination of the droplet composition by measuring at least one of capacitance, resistance, or impedance between said electrodes. This invention can (1) measure droplet composition, (2) compare composition against a known sample, (3) monitor droplet mixing, (4) control mixing to achieve specific mixing ratios, (5) measure the particle concentration within a droplet, (6) determine the position of particles in a droplet, and (7) monitor chemical reactions. These functions call all be performed in real time.

Abstract: A method and apparatus for moving droplets passed a porous obstructions in microfluidic devices is presented. The invention describes the process of using of an enabling droplet to allow a droplet to pass an obstruction. The enabling droplet and the unfiltered droplet approach the obstruction from opposite sides, merge together within the obstruction, and the interface on the enabling side of the droplet is actuated to pull fluid through the obstruction. This technique was successful for filters with pore sizes between 2 ?m and 72 without the use of surfactants. This invention can (1) move droplets past physical obstructions, (2) allow fluid within a particle to pass an obstruction while limiting the motion of man-made or biological particles within the droplet, (3) sort particles based on size in droplet-based microfluidic devices, or (4) provide an interface between continuous and discrete flow regions on a microfluidic device.