*2.1. Materials*

DSPC was provided by Lipoid GmbH (Ludwigshafen, Germany). PEG40-stearate and cholesterol were purchased from Sigma-Aldrich (Zwijndrecht, The Netherlands), 1,2-distearoyl-*sn*-glycero-3-phosphoethanolamine-*N*-carboxy-(polyethylene glycol) (DSPE-PEG2000) was purchased from Iris Biotech GmbH (Marktredwitz, Germany), and 1,2 distearoyl-*sn*-glycero-3-phosphoethanolamine-*N*-biotinyl(polyethylene glycol) (DSPE-PEG2000-biotin) was purchased from Avanti Polar Lipids (Alabaster, AL, USA). Perfluoro butane (C4F10) was purchased from F2 Chemicals (Preston, UK), and argon gas was purchased from Linde Gas Benelux (Schiedam, the Netherlands). Streptavidin Oregon Green 488 was purchased from BioSynthesis (Louisville, TX, USA), and Lissamine rhodamine B 1,2-dihexadecanoyl-*sn*-glycero-3-phosphoethanolamine, triethylammonium salt (rhodamine-DHPE) was purchased from Thermo Fisher (Waltham, MA, USA).
