Lipid-Assisted Formation and Dispersion of Aqueous and Bilayer-Embedded Nano-C60

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Abstract
Lipid assemblies provide a biocompatible approach for preparing aqueous nanoparticles. In this work, dipalmitoylphosphatidylcholine (DPPC) was used to assist in the formation and dispersion of C60 and nano-C60 aggregates using a modified reverse phase evaporation (REV) method. This method led to the rapid formation of aqueous nano-C60 at DPPC/C60 molar ratios from 500:1 to 100:1 (12−38 nm; verified by cryogenic transmission electron microscopy), which were present in the bulk phase and encapsulated within vesicles. In addition to forming nanoparticles, C60 was trapped within the vesicle bilayer and led to a reduction in the lipid melting temperature. Solvent extraction was used to isolate nano-C60 from the lipids and bilayer-embedded C60. Our results suggest that bilayer-embedded C60 was present as molecular C60 and as small amorphous nano-C60 (2.3 ± 0.4 nm), which clustered in the aqueous phase after the lipids were extracted. In addition to developing a new technique for nano-C60 formation, our results suggest that the lipid bilayer may be used as a hydrophobic region for dispersing and assembling small nano-C60.