High‐gravity‐assisted synthesis of aqueous nanodispersions of organic fluorescent dyes for counterfeit labeling

Organic fluorescent dyes have attracted wide interest because of their high photoluminescence quantum efficiencies. However, there are several application limitations arising from their hydrophobicity, poor dispersity and large particle sizes. These problems can be improved by preparing nanoparticles with a small size. Herein, we present a continuous approach to efficiently prepare an aqueous nanodispersion of water-insoluble organic fluorescent dye Nile red (NR) with monodispersed and uniform nanoparticles (35 nm) by high-gravity antisolvent precipitation in a rotating packed bed (RPB). In contrast, NR nanodispersions prepared using a traditional batch stirred tank (ST) had a broad size distribution (20-150 nm). Due to its small size effect and good dispersity in water, the RPB nanodispersion displayed significantly increased saturation solubility and much stronger fluorescent intensity compared to raw NR, and was obviously superior to the ST counterpart. Furthermore, NR nanodispersions were mixed with ink to draw fluorescent patterns on paper for counterfeit labeling.