Nucleation and growth during a fluorogenic precipitation in a micro-flow mapped by fluorescence lifetime microscopy

We have observed the precipitation of a fluorescent dye in a microfluidic 3D hydrodynamic mixing set up. In addition to the short fluorescence lifetime of the DBDCS molecule and to the long lifetime of its crystal, nuclei with an intermediate lifetime are observed. We show that the precipitation is slowed down by the presence of a viscous skin at the interface between water and THF. From the analysis of the decays, we map the concentration of the three species over half a million pixels and show that nucleation and growth occur all along the device by a slow diffusion of the water into the THF inner flow.