Effect of proteins on the oxidase-like activity of CeO2 nanozymes for immunoassays

Abstract

Having the benefits of low cost, excellent stability and tolerance to extreme conditions, nanozymes are a potential alternative of horseradish peroxidase (HRP) or other enzymes for bioanalytical chemistry, especially immunoassays. CeO₂ nanoparticles have oxidase-mimicking activity and can avoid the use of unstable H₂O₂. For robust assays, the effect of proteins on the activity of CeO₂ needs to be carefully studied. Herein, we studied the adsorption and desorption of bovine serum albumin (BSA) from CeO₂. The CeO₂ nanoparticles exhibited a higher protein adsorption capacity compared to the other tested metal oxide nanoparticles. Although the oxidase-like activity of CeO₂ was inhibited by BSA, low concentrations of phosphate and fluoride ions boosted the activity of protein-capped CeO₂. CeO₂ was still active under strong acidic conditions and at high temperature, while HRP lost its activity. For immunoassay development, we covered CeO₂ with an amine-modified silane for covalent conjugation to antibodies. A one-step indirect competitive ELISA for fenitrothion was developed, and an IC₅₀ value of 35.6 ng mL⁻¹ and a limit of detection of 2.1 ng mL⁻¹ were obtained.