Ultrabright Fluorescent Polymeric Nanoparticles with a Stealth Pluronic Shell for Live Tracking in the Mouse Brain

Khalin, Igor ; Hellal, Farida; Groschup, Bernhard and Plesnila, Nikolaus (2020): Ultrabright Fluorescent Polymeric Nanoparticles with a Stealth Pluronic Shell for Live Tracking in the Mouse Brain. In: Nano, Vol. 14, No. 8: pp. 9755-9770

Abstract

Visualizing single organic nanoparticles (NPs) in vivo remains a challenge, which could greatly improve our understanding of the bottlenecks in the field of nanomedicine. To achieve high single-particle fluorescence brightness, we loaded polymer poly(methyl methacrylate)-sulfonate (PMMA-SO3H) NPs with octadecyl rhodamine B together with a bulky hydrophobic counterion (perfluorinated tetraphenylborate) as a fluorophore insulator to prevent aggregation-caused quenching. To create NPs with stealth properties, we used the amphiphilic block copolymers pluronic F-127 and F-68. Fluorescence correlation spectroscopy and Förster resonance energy transfer (FRET) revealed that pluronics remained at the NP surface after dialysis (at one amphiphile per 5.5 nm2) and prevented NPs from nonspecific interactions with serum proteins and surfactants. In primary cultured neurons, pluronics stabilized the NPs, preventing their prompt aggregation and binding to neurons. By increasing dye loading to 20 wt % and optimizing particle size, we obtained 74 nm NPs showing 150-fold higher single-particle brightness with two-photon excitation than commercial Nile Red-loaded FluoSpheres of 39 nm hydrodynamic diameter. The obtained ultrabright pluronic-coated NPs enabled direct single-particle tracking in vessels of mice brains by two-photon intravital microscopy for at least 1 h, whereas noncoated NPs were rapidly eliminated from the circulation. Following brain injury or neuroinflammation, which can open the blood–brain barrier, extravasation of NPs was successfully monitored. Moreover, we demonstrated tracking of individual NPs from meningeal vessels until their uptake by meningeal macrophages. Thus, single NPs can be tracked in animals in real time in vivo in different brain compartments and their dynamics visualized with subcellular resolution.

• Item Type: Journal article
• EU Funded Grant Agreement Number: 794094
• EU Projects: Horizon 2020 > Marie Skłodowska Curie Actions > Marie Skłodowska-Curie Individual Fellowships > 794094: NEUROTARGET - Treatment of traumatic brain injury using dye-loaded polymeric nanoparticles
• Form of publication: Submitted Version
• Keywords: dye-loaded polymeric nanoparticles; fluorescent nanoparticles; pluronic coating; intravital imaging; single-particle tracking; blood−brain barrier
• Faculties: Medicine > Munich Cluster for Systems Neurology (SyNergy); Medicine > Institute for Stroke and Dementia Research (ISD)
• Subjects: 500 Science > 500 Science
• Language: English
• DFG: Gefördert durch die Deutsche Forschungsgemeinschaft (DFG) - 390857198