Ceria Nanoparticles Act Like Enzymes

Polymer-coated cerium oxide nanoparticles exhibit unique oxidase-like activity at low pH without the need for hydrogen peroxide as an oxidizing agent, a finding that could lead to simpler and less expensive immunoassays (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200805279). The nanoparticles created by Atul Asati, J. Manuel Perez, and coworkers at the University of Central Florida's Nanoscience Technology Center are robust aqueous redox catalysts. The team tested the oxidizing capability of the nanoparticles on 3,3′,5,5′-tetramethylbenzidine (TMB) and 2,2-azinobis(3-ethylbenzothizoline-6-sulfonic acid) (AzBTS), which are dyes that undergo a color change when oxidized and are commonly used in horseradish peroxidase-based bioassays. These assays usually require H₂O₂ as an oxidant to work in conjunction with the enzyme, but the ceria nanoparticles work well at pH 4 without H₂O₂. Inspired by their success, the researchers added folic acid groups to the surface of poly(acrylic acid)-coated ceria nanoparticles, enabling them to bind to folate receptors, which are overexpressed in many types of cancer cells. When the folate-modified nanoparticles were combined with lung cancer cells and subsequently incubated with TMB, the team saw a color change associated with TMB oxidation, indicating a positive test for the cancer cells.