Intrinsic Enzyme-like Activities of Cerium Oxide Nanocomposite and Its Application for Extracellular H ₂O ₂ Detection Using an Electrochemical Microfluidic Device

Abstract

Artificial enzyme mimics have gained considerable attention for use in sensing applications due to their high stability and outstanding catalytic activity. We show that cerium oxide nanosheets (NSs) exhibit triple-enzyme mimetic activity. The oxidase-, peroxidase-, and catalase-like activities of the proposed nanoparticles are demonstrated using both colorimetric and electron paramagnetic resonance (EPR) spectroscopy. On the basis of the excellent catalytic activity of cerium oxide NSs toward hydrogen peroxide, an electrochemical approach for the high-throughput detection of H ₂O ₂ in living cells was established. This report presents an analytical microfluidic chip integrated with a cerium oxide NS mimic enzyme for the fabrication of a simple, sensitive, and low-cost electrochemical sensor. Three Au microelectrodes were fabricated on a glass substrate using photolithography, and the working electrode was functionalized using cerium oxide NSs. The operation of this biosensor is based on cerium oxide NSs and presents a high sensitivity over a wide detection range, between 100 nM and 20 mM, with a low detection limit of 20 nM and a high sensitivity threshold of 226.4 μA·cm ^–2·μM ^–1. This microfluidic sensor shows a strong response to H ₂O ₂, suggesting potential applications in monitoring H ₂O ₂ directly secreted from living cells. This sensor chip provides a promising platform for applications in the field of diagnostics and sensing.