Microparticle parking and isolation for highly sensitive microRNA detection.

Isolating small objects, such as particles, cells, and molecules, in individual aqueous droplets is useful for chemical and biological assays. We have developed a simple microfluidic platform to immobilize (park) microparticles at defined locations, and isolate particles in monodisperse droplets surrounded by immiscible oil. While conventional methods can only achieve stochastic encapsulation of objects within larger droplets, our in situ method ensures that a single particle is entrapped in a similar-sized droplet, with ∼95% yield for parking and isolation. This enables time-lapse studies of reactions in confined volumes and can be used to perform enzymatic amplification of a desired signal to improve the sensitivity of diagnostic assays. To demonstrate the utility of our technique, we perform highly sensitive, multiplexed microRNA detection by isolating encoded, functional hydrogel microparticles in small aqueous droplets. Non-fouling hydrogel microparticles are attractive for microRNA detection due to favorable capture kinetics. By encapsulating these particles in droplets and employing a generalizable enzyme amplification scheme, we demonstrate an order of magnitude improvement in detection sensitivity compared to a non-amplified assay.