Optimizing the Fluorescence Properties of Nanoemulsions for Single Particle Tracking in Live Cells

Nanoemulsions (NEs) are biocompatible lipid nanoparticles composed of an oily core stabilized by a surfactant shell. It is acknowledged that the surface decoration with poly­(ethylene glycol), through the use of nonionic surfactants, confers high stealth in biological medium with reduced nonspecific interactions. Tracking individual NE by fluorescence microscopy techniques would lead to a better understanding of their behavior in cells and thus require the development of bright single particles with enhanced photostability. However, the understanding of the relationship between the physicochemical properties and chemical composition of the NEs, on the one hand, and its fluorescence properties of encapsulated dyes, on the other hand, remains limited. Herein, we synthesized three new dioxaborine barbituryl styryl (DBS) dyes that displayed high molar extinction coefficients (up to 120 000 M–1 cm–1) with relatively low quantum yields in solvents and impressive fluorescence enhancement when dissolved in viscous oils (up to 0.98). The reported screening of nine different oils allowed disclosing a range of efficient “oil/dye” couples and understanding the main parameters that lead to the brightest NEs. We determine vitamin E acetate/DBS-C8 as the representative most efficient couple, combining high dye loading capabilities and low aggregation-induced quenching, leading to