One of the most powerful aspects of microfluidics is the potential to sort microdroplets based on some measurable characteristic, such as fluorescence intensity. There are many different ways to do this (acoustic, electric, magnetic, optical and inertia), the choice of which depends on your given application.
Here, we are very happy to report the success of droplet sorting based on chlorophyll content. This was achieved through application of an electric field in response to chlorophyll concentration measured by a laser. This can be seen in the video below, droplets enter from an inlet channel to a Y-junction, if they do not contain cells they pass into the lower channel. If a droplet containing a cell passes under the detector, a short flash can be observed, and the electrodes at the top of the picture are activated pulling the droplet into the upper channel. To achieve this is was necessary to re-design the sorting chip (from an earlier chip made for working with cyanobacteria) to include a wider outlet channel.
As this phase of the project comes to an end I'm pleasantly surprised to say nearly all our goals have been achieved! The only part remaining would be to create opensource software for this project, but due to time constraints this has not been possible.
Moving forward, we have obtained funding for a follow-up project courtesy of the OpenPlant Fund. So in the coming months we will be concentrating on developing methods for on-chip transformation of protoplasts. The reason for this is currently very large volumes of DNA are required for transformation (>10ug), and this is the last remaining bottleneck before we will truly be able to perform high-throughput analyses.