Polyelectrolyte functionalization of ceria nanozymes: linking dispersion stability and enzyme-like activity

Cerium oxide (CeNPs) nanozymes represent a versatile class of biocatalytic nanomaterials capable of mimicking multiple enzyme functions, however, their practical application is often hindered by limited colloidal stability. Herein, the interaction of oppositely charged polyelectrolytes, namely heparin (HEP), chondroitin sulfate (CS), poly(acrylic acid) (PAA) and methylglycol chitosan (MGC), with CeNPs was investigated with respect to dispersion stability, peroxidase-like activity and biocompatibility. Distinct charging and aggregation regimes were quantitatively identified over a wide range of polyelectrolyte-to-particle mass ratios. At high surface coverage, adsorption of the macromolecules markedly enhanced resistance against salt-induced aggregation owing to electrosteric repulsion. Surface functionalization also improved the peroxidase-like operation of the CeNPs, with polyanion-coated particles exhibiting substantially higher enzymatic activity than the bare nanozymes. Cell viability assays confirmed excellent biocompatibility of both pristine and functionalized CeNPs, with no detectable cell death upon incubation with the nanozymes. These findings demonstrate that polyelectrolyte adsorption provides an effective strategy to simultaneously improve the colloidal stability and biocatalytic performance of CeNPs, widening their implementation in biomedical and industrial applications.