Mn-Etched Zeolitic Imidazolate Framework-67 Nanostructures for Biomimetic Superoxide Anion Sensing

It is a great challenge to detect superoxide anions (O₂^•–) with low level concentrations and short half-life in biological systems. Herein, mild and facile Mn etching for zeolitic imidazolate framework-67 (ZIF-67) was used to synthesize Mn/ZIF-67 with a hydrangea-like nanostructure for biomimetic sensing of O₂^•– released from living cells. The tailored optimal Mn/ZIF-67 sensor achieves a high selectivity, a fast response time (1.6 s), a broad linear detection range (1.5 nM–10 μM), an ultralow detection limit (0.8 nM), and a remarkably high sensitivity (439.2 μA μM^–1 cm^–2) that ranks the best among all reported conventional Mn- and Co-compound-based nanozymes such as Co₂P and Mn₃(PO₄)₂. The excellent sensing performances are attributed to the Mn etching-generating hydrangea-like nanostructure for a significantly increased reaction surface area and coordinating Mn²⁺ with Co²⁺ to raise the oxidation state of Co²⁺ for fast electron transfer during the oxidation of O₂^•–. This work holds great potential for a highly sensitive O₂^•– nanozyme sensor in practical clinical diagnosis and bioscience research, while shedding fundamental light on designs of sensitive nanozyme sensors by incorporating two metal ions with largely different negativity for an efficient electrocatalytic process, thereby possessing universal significance.