A Bifunctional Poly(ethylene glycol) Silane Immobilized on Metallic Oxide-Based Nanoparticles for Conjugation with Cell Targeting Agents

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Abstract
A trifluoroethylester-terminal poly(ethylene glycol) (PEG) silane was synthesized and self-assembled on iron oxide nanoparticles. The nanoparticle system thus prepared has the flexibility to conjugate with cell targeting agents via either carboxylic or amine terminal groups for a number of biomedical applications, including magnetic resonance imaging (MRI) and controlled drug delivery. The trifluoroethylester silane was synthesized by modifying a PEG diacid to form the corresponding bistrifluoroethylester (TFEE), followed by a reaction with 3-aminopropyltriethoxysilane (APS). The APS coupled with PEG chains confers the stability of PEG self-assembled monolayers (SAMs) and increases the PEG packing density on nanoparticles by establishing hydrogen bonding between the carbonyl and amine groups present within the monolayer structure. The success of the synthesis of the PEG TEFE silane was confirmed with 1H NMR and Fourier transform infrared spectroscopy (FTIR). The conjugating flexibility of the PEG TEFE was demonstrated with folic acid that had carboxylic acid groups and amine terminal groups, respectively, and was confirmed by FTIR. TEM analysis showed the well-dispersed nanoparticles before and after they were coated with PEG and folic acid.