Investigation of controlled solvent exchange precipitation of fluorescent organic nanocrystals

The process of bottom-up organic nanocrystal precipitation is influenced by various parameters, like precursor concentration, flow rates (if using a mixing system) and presence of supporting substances, e.g. surfactants. Knowing that supporting substances are often undesired and harmful in the context of biomedical engineering and drug technology, designing an efficient, controllable and surfactant-free process is important. Organic nanocrystals can be used in delivery of poorly soluble drugs and in the optical detection of tumors when fluorescent nanocrystals are employed. Both drugs and fluorescent agents take the advantage of a small size, purity and possibilities of functionalization for targeting cancer cells. We investigated key process parameters in the precipitation of [2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) fluorescent nanocrystals in a hydrodynamic focusing device. We have identified the influence of fluorescent dye solution concentration and water/dye solution flow rate ratio on obtained product polydispersity, size, zeta potential, and fluorescence. We have compared the results with bulk precipitated crystals. Device-obtained nanocrystals present higher monodispersity, diameters in a range of 90-150 nm and low fluorescence compared to crude crystals. Moreover, for high flow rate ratio and high dilutions of the dye, the nanocrystals present both monodispersity and intense fluorescence, even higher than crude crystals obtained in the bulk mixing process.