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.