Surface Modification of Co₃O₄ Nanoplates as Efficient Peroxidase Nanozymes for Biosensing Application

Nanomaterial-based mimetic enzymes, called nanozymes, received more and more attention in recent decades; however, their lack of biocompatibility limited the biomedical applications, which could be solved by surface modification. In this work, the Co₃O₄ nanoplates were modified by different functional groups, including the amino group, carboxyl group, hydroxyl group, and sulfhydryl group (NH₂-Co₃O₄, COOH-Co₃O₄, OH-Co₃O₄, and SH-Co₃O₄). And the modified Co₃O₄ nanoplates were characterized by XRD, SEM, TEM, XPS, FTIR, TG, and the Zeta potential, verifying the successful modification of different functional groups. Their mimetic peroxidase properties and kinetics process were further studied and showed that the order of their catalytic activities was as follows: NH₂-Co₃O₄ > SH-Co₃O₄ > COOH-Co₃O₄ > pure Co₃O₄ > OH-Co₃O₄, and the catalysis of modified Co₃O₄ nanozymes all followed Michaelis-Menten kinetics. The results indicated that the different functional groups changed their electron transfer ability, and further affected their catalytic activity. H₂O₂ detection was selected as an application model system to evaluate the modified Co₃O₄ nanozymes. Compared with other Co₃O₄ nanozymes, a wider linear range from 0.01 to 40 mmol L^-1 and a lower detection limit of 1.5 μmol L^-1 was constructed with NH₂-Co₃O₄ nanozymes. The results suggested that surface modification by functional groups was a robust strategy to improve the application of Co₃O₄ nanozymes. The enhanced catalytic activity and good biocompatibility of modified Co₃O₄ nanozymes provided valuable materials for the relative application, such as medical detection and antioxidation.