Electrosteric enhanced stability of functional sub-10 nm cerium and iron oxide particles in cell culture medium

TL;DR

This study demonstrates that poly(acrylic acid) coatings significantly enhance the long-term stability of sub-10 nm cerium and iron oxide nanoparticles in cell culture media through electrosteric interactions.

Contribution

It introduces a simple coating protocol using poly(acrylic acid) that improves nanoparticle stability in complex biological environments, outperforming other tested ligands and polymers.

Findings

Poly(acrylic acid) fully stabilizes nanoparticles long-term.

Electrosteric interactions are key to stability.

Anionic polymer coatings are effective alternatives.

Abstract

Applications of nanoparticles in biology require that the nanoparticles remain stable in solutions containing high concentrations of proteins and salts, as well as in cell culture media. In this work, we developed simple protocols for the coating of sub-10 nm nanoparticles and evaluated the colloidal stability of dispersions in various environments. Ligands (citric acid), oligomers (phosphonate-terminated poly(ethylene oxide)) and polymers (poly(acrylic acid)) were used as nanometer-thick adlayers for cerium (CeO2) and iron (gamma-Fe2O3) oxide nanoparticles. The organic functionalities were adsorbed on the particle surfaces via physical (electrostatic) forces. Stability assays at high ionic strength and in cell culture media were performed by static and dynamic light scattering. Among the three coating examined, we found that only poly(acrylic acid) fully preserved the dispersion stability on the long term (> weeks). The improved stability was explained by the multi-point attachments of the chains onto the particle surface, and by the adlayer-mediated electrosteric interactions. These results suggest that anionically charged polymers represent an effective alternative to conventional coating agents.