(357d) Enzyme-Mimetic Antioxidant Luminescent Nanoparticles for Highly Sensitive Hydrogen Peroxide Biosensing

Hydrogen peroxide (H₂O₂) is an abundant molecule associated with biological implications and reacts with natural enzymes, such as catalase. Thus, H₂O₂ quantification constitutes a powerful tool for detection of disease biomarkers linked to enzyme-based assays. However, the optical H₂O₂ biosensing without organic-dyes in biological media and at low, submicromolar, concentrations has yet to be achieved. Herein, we rationally design biomimetic artificial enzymes based on antioxidant CeO₂ nanoparticles that become luminescent upon their Eu³⁺ doping. We vary systematically their diameter from 4 to 16 nm and study their catalase-mimetic antioxidant activity, manifested as catalytic H₂O₂ decomposition in aqueous solutions, revealing a strong nanoparticle surface area dependency. The interaction with H₂O₂ influences distinctly the nanozyme luminescence rendering them highly sensitive H₂O₂ biosensors down to 0.15 mM (5.2 ppb) in biologically-relevant solutions. Our results link two, so far, unrelated research domains, the CeO₂ nanoparticle antioxidant activity and luminescence by rare-earth doping. When these nanozymes are coupled with alcohol oxidase, biosensing can be extended to ethanol exemplifying how their detection potential can be broadened to additional biologically relevant metabolites. The biomimetic artificial enzyme developed here could serve as a starting point of sophisticated in vitro assays towards highly sensitive detection of disease biomarkers.