posted on 2019-03-07, 00:00authored byXinyue Wang, Nicolas Anton, Pichandi Ashokkumar, Halina Anton, Tkhe Kyong Fam, Thierry Vandamme, Andrey S. Klymchenko, Mayeul Collot
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 <50 nm ultrabright
NEs (with brightness as high as 30 × 106 M–1 cm–1) with negligible dye leakage in biological
media. Beyond a comprehensive optical and physicochemical characterization
of fluorescent NEs, cellular two-photon excitation imaging was performed
with polymer-coated cell penetrating NEs. Thanks to their impressive
brightness and photostability, NEs displaying different charge surfaces
were microinjected in HeLa cells and were individually tracked in
the cytosol to study their relative velocity.