title: Counterion-enhanced cyanine dye loading into lipid nano-droplets for single-particle tracking in zebrafish.
abstract: Superior brightness of fluorescent nanoparticles places them far ahead of the classical fluorescent dyes in the field of biological imaging. However, for in vivo applications, inorganic nanoparticles, such as quantum dots, are limited due to the lack of biodegradability. Nano-emulsions encapsulating high concentrations of organic dyes are an attractive alternative, but classical fluorescent dyes are inconvenient due to their poor solubility in the oil and their tendency to form non-fluorescent aggregates. This problem was solved here for a cationic cyanine dye (DiI) by substituting its perchlorate counterion for a bulky and hydrophobic tetraphenylborate. This new dye salt, due to its exceptional oil solubility, could be loaded at 8 wt% concentration into nano-droplets of controlled size in the range 30-90 nm. Our 90 nm droplets, which contained >10,000 cyanine molecules, were >100-fold brighter than quantum dots. This extreme brightness allowed, for the first time, single-particle tracking in the blood flow of live zebrafish embryo, revealing both the slow and fast phases of the cardiac cycle. These nano-droplets showed minimal cytotoxicity in cell culture and in the zebrafish embryo. The concept of counterion-based dye loading provides a new effective route to ultra-bright lipid nanoparticles, which enables tracking single particles in live animals, a new dimension of in vivo imaging.
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France.
authors.forename: Vasyl N
authors.initials: VN
authors.lastname: Kilin
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France.
authors.forename: Halina
authors.initials: H
authors.lastname: Anton
authors.affiliation: Laboratoire de Conception et Application de Molecules Bioactives, UMR CNRS 7199, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Anton
authors.affiliation: IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Inserm U964, CNRS UMR7104, Université de Strasbourg, 1 rue Laurent Fries, 67404 Illkirch, France.
authors.forename: Emily
authors.initials: E
authors.lastname: Steed
authors.affiliation: IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Inserm U964, CNRS UMR7104, Université de Strasbourg, 1 rue Laurent Fries, 67404 Illkirch, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Vermot
authors.affiliation: Laboratoire de Conception et Application de Molecules Bioactives, UMR CNRS 7199, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France.
authors.forename: Thierry F
authors.initials: TF
authors.lastname: Vandamme
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Mely
authors.affiliation: Laboratoire de Biophotonique et Pharmacologie, UMR 7213 CNRS, Université de Strasbourg, Faculté de Pharmacie, 74, Route du Rhin, 67401 Illkirch, France. Electronic address: andrey.klymchenko@unistra.fr.
authors.forename: Andrey S
authors.initials: AS
authors.lastname: Klymchenko
mesh_terms: D000792:Angiography; D000818:Animals; D002232:Carbocyanines / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D004655:Emulsions; D057927:Hydrophobic and Hydrophilic Interactions; D057054:Molecular Imaging / Q000379:methods*; D053758:Nanoparticles / Q000737:chemistry*; D061848:Optical Imaging; D045663:Quantum Dots; D015027:Zebrafish / Q000097:blood / Q000196:embryology
chemical_list: D002232:Carbocyanines; D004396:Coloring Agents; D004655:Emulsions
keywords: counterion-assisted dye loading; fluorescence; lipid; nano-emulsion; nanoparticle; singleparticle tracking