Synthesis of Stable Cerium Oxide Nanoparticles Coated with Phosphonic Acid-Based Functional Polymers
Abstract
Functionalpolymers, such as poly(ethylene glycol) (PEG), terminatedwith a single phosphonic acid, hereafter PEG( ik)-Ph are often applied to coat metal oxide surfaces duringpost-synthesis steps but are not sufficient to stabilize sub-10 nmparticles in protein-rich biofluids. The instability is attributedto the weak binding affinity of post-grafted phosphonic acid groups,resulting in a gradual detachment of the polymers from the surface.Here, we assess these polymers as coating agents using an alternativeroute, namely, the one-step wet-chemical synthesis, where PEG( ik)-Ph is introduced with cerium precursorsduring the synthesis.
Characterization of the coated cerium oxidenanoparticles (CNPs) indicates a core-shell structure, wherethe cores are 3 nm cerium oxide and the shell consists of functionalizedPEG polymers in a brush configuration. Results show that CNPs coatedwith PEG(1k)-Ph and PEG(2k)-Ph are of potentialinterest for applications as nanomedicines due to their high Ce(III)content and increased colloidal stability in cell culture media.
Wefurther demonstrate that the CNPs in the presence of hydrogen peroxideshow an additional absorbance band in the UV-vis spectrum,which is attributed to Ce-O-2 (2-) peroxo-complexes and could be used in the evaluation of their catalyticactivity for scavenging reactive oxygen species.