Engineering Well-Characterized PEG-Coated Nanoparticles for Elucidating Biological Barriers to Drug Delivery

Poly(ethylene glycol) (PEG) coatings can substantially reduce nanoparticle uptake and clearance by immune cells as well as nonspecific interactions with the biological environment, thus potentially improving nanoparticle circulation times and biodistribution in target tissues such as tumors. Naturally, the "stealth" properties of PEG coatings are critically dependent on the density and conformation of surface PEG chains. However, there are significant technical hurdles to both generating sufficiently dense PEG coatings on nanoparticles and precisely characterizing their PEG grafting densities. Here, we describe methods for preparing PEGylated polymeric nanoparticles with precisely tunable PEG coatings without the use of organic solvents, quantifying PEGylation efficiency and density using a standard fluorescence assay, and evaluating nanoparticle uptake by immune cells using flow cytometry.