White Mn-MOF nanozymes with peroxidase-activity specificity overcome color and O₂ effects on colorimetric test strips

Given the promising prospect of nanozymes in colorimetric test strips, it is essential to eliminate the interferences of their multi-activities and various colors on the test strip. Here, white Mn-based metal-organic frameworks (Mn-MOFs) with ultrathin 2D morphology (3 nm thick) were successfully synthesized by a simple ultrasonic approach. The origin of the white optical property in Mn-MOFs was systematically investigated, revealing that it stems from specific metal-ligand coordination polymerization rather than morphological features or defect states. Mn-MOF nanozymes possessed exclusive peroxidase-mimicking activity rather than oxidase-like activity, effectively resisting O₂ interference during colorimetric assay. Moreover, Mn-MOF nanozymes displayed unique substrate selectivity without additional modification. Unlike other colored nanozymes, the whiteness of Mn-MOF nanozymes enhanced the paper's whiteness, boosting contrast for colorimetric detection on test strip. This study pioneers a systematic investigation into the origin of whiteness in MOF nanozymes. The coordination-defined properties enable interference-free optical design and O₂-resistant on-site detection.