An in vitro imaging system to evaluate the stealth function of nanoparticles against mouse macrophages was established using fluorescent organosilica nanoparticles. Surface-functionalized organosilica nanoparticles with polyethylene glycol (PEG) were prepared by a one-step process, resulting in a brush-type PEG layer. A simultaneous dual-particle administration approach enabled us to evaluate the stealth function of nanoparticles with respect to single cells using time-lapse fluorescent microscopic imaging and flow cytometry analyses. Single-cell imaging and analysis revealed various patterns and kinetics of bare and PEGylated nanoparticle uptake. The PEGylated nanoparticles revealed a stealth function against most macrophages (PEG-sensitive macrophages); however, a stealth function against certain macrophages (PEG-insensitive macrophages) was not observed. We identified and characterized the PEG-resistant macrophages that could take up PEGylated nanoparticles at the same level as bare nanoparticles.
Keywords: accelerated blood clearance; macrophages; polyethylene glycol; single-cell analysis; stealth nanoparticles.