Easy formation of functional liposomes in water using a pH- responsive microbial glycolipid: encapsulation of magnetic and up-converting nanoparticles

30 The compartmentalization of colloids into topologically closed, vesicular, microphases offers 31 an attractive mean to concentrate a functional cargo in aqueous solutions for a range of 32 biomedical, cosmetic, and biotechnological applications. In this paper, we develop a simple, 33 phospholipid-free, phase change method employing a pH-responsive glycolipid. The method is 34 applied to the encapsulation of a sonicated, metastable, aqueous dispersion of functional 35 colloids in the lumen of lipid vesicles: uncoated magnetic maghemite -Fe2O3 and oleic-acid 36 coated upconverting NaYF4:Yb/Ln (Ln= Er or Tm) nanoparticles (NPs). We find a stable 37 liposomal dispersion containing a sub-population of crowded liposomes with high 38 concentrations of NPs. The encapsulated NPs, formed at nearly neutral pH and room 39 temperature, are stable over time and towards extrusion. The vesicular microphase is entirely 40 composed of pH-responsive glycolipids, which undergo a pH-mediated mesoscopic structural 41 transition from an open lamellar (2 < pH < 4) to topologically closed vesicular state (pH > 4). 42 3 We also show that encapsulation successfully works with a stable colloidal aqueous dispersion 43 of iron clusters stabilized in ferritin cages. This compartmentalization approach combining self-44 assembly with an orthogonal nonequilibrium dispersion of nanoparticles shows untapped 45 potential for synthesizing unusual classes of mixed matter. 46 47 Introduction 48