Functional
polymers, such as poly(ethylene glycol) (PEG), terminated
with a single phosphonic acid, hereafter PEGik-Ph are often applied to coat metal oxide surfaces during
post-synthesis steps but are not sufficient to stabilize sub-10 nm
particles in protein-rich biofluids. The instability is attributed
to 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 alternative
route, namely, the one-step wet-chemical synthesis, where PEGik-Ph is introduced with cerium precursors
during the synthesis. Characterization of the coated cerium oxide
nanoparticles (CNPs) indicates a core–shell structure, where
the cores are 3 nm cerium oxide and the shell consists of functionalized
PEG polymers in a brush configuration. Results show that CNPs coated
with PEG1k-Ph and PEG2k-Ph are of potential
interest for applications as nanomedicines due to their high Ce(III)
content and increased colloidal stability in cell culture media. We
further demonstrate that the CNPs in the presence of hydrogen peroxide
show an additional absorbance band in the UV–vis spectrum,
which is attributed to Ce–O22– peroxo-complexes and could be used in the evaluation of their catalytic
activity for scavenging reactive oxygen species.