Abstract
Magnetic nanoparticles (MNPs) are widely used in cell sorting, organelle selection, drug delivery, cell delivery, and cell tracking applications. However, organelle manipulation in living cells has been limited due to the endocytic uptake and sequestration of MNPs. Here, we introduce a method for modifying MNPs with fusogenic liposomes that facilitate MNP passage directly into the cytosol. MNPs were enclosed in fusogenic liposomes that exhibit a core–shell structure under a transmission electron microscope (TEM). The lipid-to-MNP ratio was optimized for one layer of liposome coating around each MNP, so that MNPs were delivered to the cytosol without endosomal or liposomal coatings. After incubation with the retinal pigment epithelial cell line ARPE-19, single-layer liposome-coated MNPs exhibited the highest MNP delivery efficiency. Although uncoated MNPs are taken up through endocytosis, less than 15% of the fusogenic liposome-coated MNPs co-localized with early endosomes. MNPs delivered by fusogenic liposomes showed cytosolic localization early on and increased lysosomal localization at later time points. The movement of intracellular MNPs could be manipulated with an external magnet to estimate cytosolic viscosity. Bypassing endocytosis in this way allowed efficient delivery of MNPs to the cytosol, potentially allowing for the targeting of specific organelles and controlling their motion in living cells.
Highlights
Labeling cells with nanoparticles has broad applications in cell imaging, tracking, manipulation, and drug delivery.[1,2,3,4] Iron oxide nanoparticles have been extensively studied for their magnetic properties and wide applications in biology and life science.[5,6] First, they are widely used to track cells in vivo using magnetic resonance imaging (MRI)[7] and as a contrast agent for the emerging imaging modality known as magnetic particle imaging.[8]
The size distribution is shown in Electronic supplementary information (ESI) Fig. S1.† Before coating Magnetic nanoparticles (MNPs) with liposomes, MNPs were conjugated with Alexa Fluor 647 via Nhydroxysuccinimide ester chemistry
The dye conjugation increased the hydrodynamic size of MNPs from 128 nm to 139 nm and kept the polydispersity index (PDI) within 0.2, which indicates a small size distribution of the MNPs before and a er dye conjugation
Summary
Labeling cells with nanoparticles has broad applications in cell imaging, tracking, manipulation, and drug delivery.[1,2,3,4] Iron oxide nanoparticles have been extensively studied for their magnetic properties and wide applications in biology and life science.[5,6] First, they are widely used to track cells in vivo using magnetic resonance imaging (MRI)[7] and as a contrast agent for the emerging imaging modality known as magnetic particle imaging.[8]. The average sizes of liposome-coated MNPs were 175, 192, and 198 nm when the initial lipid-to-MNP ratios were 0.14, 0.28, and 0.55, respectively. Liposomal coating increased the zeta potential of MNPs, which turned from negative to positive when the initial lipid-to-MNP ratio increased from 0.28 to 0.55 (Fig. 2h).
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