Well-Defined SiO2@P(EtOx-stat-EI) Core-Shell Hybrid Nanoparticles via Sol-Gel Processes

Abstract

Positively charged nanoparticles (NPs) are very interesting for biomedical and pharmaceutical applications, such as nonviral gene delivery. Here, the synthesis of SiO2 nanoparticles with a covalently grafted poly(2-ethyl-2-oxazoline) (PEtOx) shell (SiO2@PEtOx) is presented. PEtOx with a degree of polymerization of 20 and 38 is synthesized via microwave supported cationic ring-opening polymerization and subsequently end-functionalized with a triethoxysilyl linker for subsequent grafting to silica particles with hydrodynamic radii of 7, 31, and 152 nm. The resulting SiO2@PEtOx particles are characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM, cryoTEM), and scanning electron microscopy (SEM) to determine changes in particle size. Thermal gravimetrical analysis is used to quantify the amount of polymer on the silica surface. Subsequent in situ transformation of SiO2@PEtOx particles into SiO2@P(EtOx-stat-EI) (poly(2-ethyl-2-oxazoline-stat-ethylene imine) grafted silica particles) under acidic conditions inverts the surface charge from negative to positive according to ζ-potential measurements. The P(EtOx-stat-EI) shell could be used for the deposition of Au NP afterward. The synthesis of SiO2 nanoparticles (NPs) with a covalently grafted poly(2-ethyl-2-oxazoline) or (poly(2-ethyl-2-oxazoline-stat-ethylene imine) shell (SiO2@PEtOx and SiO2@P(EtOx-stat-EI)) is presented. Therefore, PEtOx is end-functionalized with a triethoxysilyl linker and hydrolyzed under acidic conditions after the grafting-to process. The P(EtOx-stat-EI) shell could also be used for the deposition of Au NP afterward.