Colorimetric detection platforms based on enzyme-mimetic activities of metal (M)-substituted vanadates (MxVyOz): A review of synthesis, mechanisms, and sensing applications

Recently, rapid and simple analyte detection has attracted consideration among various sensing methods. In this context, enzyme-mimicking chromogenic reactions have emerged as platforms for colorimetric detection of final targets. Nanoscale materials exhibiting enzyme-mimicking properties, called nanozymes, have garnered significant attention as functional analogs of natural enzymes. Nanozymes offer several advantages, including inherent robustness, high catalytic activity, ease of storage, and cost-effectiveness, and can be synthesized using simple and environmentally friendly methods. Among these, metal-substituted vanadium oxides (MVOs), with the general formula M_xV_yO_z (where M denotes a substituting metal), have attracted considerable interest as nanozymes. These materials have shown promise in oxidoreductase-like applications due to their unique crystal structures and the presence of valence-state-rich metal centers. This review demonstrates the catalytic potential of MVOs, highlighting how the coexistence of multiple oxidation states in the metal centers can induce synergistic effects that enhance their enzyme-like behavior. The possible mechanisms of their intrinsic oxidoreductase-mimicking behavior are discussed in the context of chromogenic substrate oxidation. Moreover, recent applications of MVO-based colorimetric nanozyme systems—comprising MVOs, chromogenic substrates, and oxidizing agents—in various fields, including analytical biosensing, food safety, environmental monitoring, and antibacterial treatments, are completely highlighted.