Rational Development of Co‐Doped Mesoporous Ceria with High Peroxidase‐Mimicking Activity at Neutral pH for Paper‐Based Colorimetric Detection of Multiple Biomarkers

Peroxidase-mimicking nanozymes have been extensively studied, however, their application is limited by the requirement for an acidic pH. Herein, the development of Co-doped mesoporous cerium oxide (Co-m-ceria) is reported, which operates optimally at a near-neutral pH and exhibits a peroxidase-like catalytic efficiency that is 600-times higher than that of pristine m-ceria. Density functional theory (DFT) calculations for the application of pristine and various metal-doped m-ceria in peroxidase-like reactions under different pH environments are conducted to select Co as the appropriate dopant. The high peroxidase-like activity of Co-m-ceria under neutral conditions and its mesoporous nature enable its application in a one-pot cascade reaction system, wherein biomarkers of oxidative enzymes can be detected without altering the pH. Five different oxidative enzymes are immobilized in the pores of Co-m-ceria at high loadings, followed by incorporation of the enzyme-containing Co-m-ceria in paper microfluidic devices for the convenient and simultaneous detection of multiple biomarkers. The Co-m-ceria-incorporated paper microfluidic device enables the selective and sensitive determination of multiple biomarkers using a smartphone-acquired image. This study demonstrates the potential of the rational design of nanozymes and their application in paper microfluidic devices, laying the groundwork for future applications of nanozymes in point-of-care testing environments.