Ph.D Thesis

Ph.D StudentShemesh Jonathan
SubjectNanoliter Droplet-Based Microfluidics for Chemical and
Biological Assays
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor PROF. Shulamit Levenberg


Droplet-based micro-devices provide attractive platforms for a wide range of applications which rely on the ability to perform many parallel experiments within discrete and isolated volumes. The microscopic dimensions of the droplets promote rapid mixing and accommodation of large droplet ensembles on a single chip. Applications, ranging from enzymatic, single cell to whole-animal assays, were successfully demonstrated.

Much of the research on droplet-based micro-devices has focused on developing micro-devices with single flow focusing configurations, where uniformly sized droplets with known and fixed composition are produced. This droplet uniformity offers the advantage that large numbers of droplet-based experiments can be set, all sharing similar conditions.

However, this uniformity also limits the ability to conduct more complex experiments, such as high-throughput screening. For assays of this type, a module that generates single droplets, each with a different, controllable, and precise reagent concentration is required as well as an assay that supports droplet sorting.

To address those needs we designed two types of platforms. One for droplet sorting and another one for controlling droplet chemical content. Both modules were operated on-demand, which in the case of sorting, allow one to choose a specific droplet and sort it to a side channel and in the case of concentration control, generate a single droplet with unique chemical composition which was set a priori.

Furthermore, droplet based devices capture much attention due to the demonstrated ability to grow single cells in aqueous droplets. In order to investigate cells over prolonged periods of time, of hours up to days, cell-encapsulated droplets must remain stationary. In spite of its relevance, setting up such stationary droplet array remained difficult. One of the main limitations arose from pressure coupling between drop-generation and drop-capture events, and the requirement to adjust droplet volume to trap size.

To address this, we developed a new platform that overcome these problems and generates hundreds of stabilized, stationary nanoliter droplets in a pressure insensitive manner.  We encapsulated single live cells in droplets and monitored their metabolic activity. Using this method we also determined initial bacterial concentration in sample liquid. The device has multiple advantages such as simplicity, very low reagent consumption and portability.

To summarize, we introduce in this thesis three different platforms that improve droplet based micro-devices; a droplet sorting, controlling droplet chemical concentration, and droplet incubation array (termed SNDA) to rapidly generate hundreds of stationary droplets for further encapsulated cell inspection and analysis.