Probing the Role of Charged Functional Groups on Nanoparticles Grafted with Polyglycerol in Protein Adsorption and Cellular Uptake

In biofluids, charged functional groups on the surface of nanoparticles (NPs) interact with cells through the protein corona. However, the cascade effects of charged groups on corona formation and cellular uptake remain unclear. Herein, carboxy, sulfate, and amino groups are quantitatively introduced at the periphery of polyglycerol (PG)-grafted nanodiamond and superparamagnetic iron oxide NP to probe their roles in corona formation and cellular uptake. The uptake efficiency and intracellular aggregation state of NPs are revealed to correlate with protein affinity of the charged groups; sulfate at lower density and carboxylate exhibit no affinity to proteins, inducing negligible or no cellular uptake. In contrast, sulfate at higher density and ammonium associate with fetal bovine serum proteins to alter the aggregation state of the internalized NPs. It is further demonstrated that the distinct protein corona profiles on NP-PG-OSO₃⁻ and NP-PG-NH₃⁺ surfaces dictate their uptake mechanism. The protein corona of NP-PG-OSO₃⁻ suppresses cellular uptake via downregulation of macropinocytosis and clathrin-mediated endocytosis, whereas that of NP-PG-NH₃⁺ enhances uptake through upregulation of macropinocytosis and caveolae-mediated endocytosis. This study clarifies the elusive role of the charged groups in protein adsorption and cellular uptake, which sheds light on NP design for controlled cellular uptake and theranostics in nanomedicine.