Enhanced Intraliposomal Metallic Nanoparticle Payload Capacity Using Microfluidic-Assisted Self-Assembly

Hybrids composed of liposomes (L) and metallic nanoparticles (NPs) hold great potential for imaging and drug delivery purposes. However, the efficient incorporation of metallic NPs into liposomes using conventional methodologies has so far proved to be challenging. In this study, we report the fabrication of hybrids of liposomes and hydrophobic gold NPs of size 2-4 nm (Au) using a microfluidic-assisted self-assembly process. The incorporation of increasing amounts of AuNPs into liposomes was examined using microfluidics and compared to L-AuNP hybrids prepared by the reverse-phase evaporation method. Our microfluidics strategy produced L-AuNP hybrids with a homogeneous size distribution, a smaller polydispersity index, and a threefold increase in loading efficiency when compared to those hybrids prepared using the reverse-phase method of production. Quantification of the loading efficiency was determined by ultraviolet spectroscopy, inductively coupled plasma mass spectroscopy, and centrifugal field flow fractionation, and qualitative validation was confirmed by transmission electron microscopy. The higher loading of gold NPs into the liposomes achieved using microfluidics produced a slightly thicker and more rigid bilayer as determined with small-angle neutron scattering. These observations were confirmed using fluorescent anisotropy and atomic force microscopy. Structural characterization of the liposomal-NP hybrids with cryo-electron microscopy revealed the coexistence of membrane-embedded and interdigitated NP-rich domains, suggesting AuNP incorporation through hydrophobic interactions. The microfluidic technique that we describe in this study allows for the automated production of monodisperse liposomal-NP hybrids with high loading capacity, highlighting the utility of microfluidics to improve the payload of metallic NPs within liposomes, thereby enhancing their application for imaging and drug delivery.