Synchronous modulation of fluorescence and oxidase-mimicking activity in a Mn-based MOF nanozyme via post-synthetic metal exchange for Cu²⁺ sensing.

Authors

Linying Cheng, Xiang Liu, Zixin Zhang, Jing Liu, Jianru Tang, Xiaohua Zhu, Youyu Zhang, Meiling Liu

Published in

Talanta. Volume 311. Pages 130300. Jul 11, 2026. Epub Jul 11, 2026.

Abstract

Copper ions (Cu²⁺) are essential micronutrients but become hazardous when accumulated in excess, necessitating reliable, sensitive, and field-deployable detection methods. Herein, we report a fluorescent Mn-based MOF nanozyme (Mn-TCPP) that exhibits intrinsic oxidase-like activity, capable of catalyzing the oxidation of non-fluorescent o-phenylenediamine (OPD) to fluorescent 2,3-diaminophenazine (DAP) with an emission peak at 560 nm, while the Mn-TCPP itself displays characteristic fluorescence at 655 nm. Upon exposure to Cu²⁺, the stronger affinity of Cu²⁺ toward the porphyrinic TCPP ligand displaces Mn²⁺ from the framework, forming Cu-TCPP. This metal-exchange process simultaneously quenches the 655 nm fluorescence of the MOF and attenuates its oxidase-mimicking activity, whereas free Cu²⁺ in solution independently catalyzes OPD oxidation, further enhancing the 560 nm emission. Leveraging this dual-response mechanism, we develop a ratiometric fluorescence sensing strategy for Cu²⁺ detection based on the intensity ratio F₅₆₀/F₆₅₅. The calibration curve follows a linear equation: F₅₆₀/F₆₅₅ = 0.201x-0.001 (0.2-10 μM, R² = 0.985) and y = 0.002x+2.061 (10-100 μM, R² = 0.994) with the limit of detection (LOD) of 81 nM (S/N = 3). The sensor exhibits excellent selectivity over competing metal ions, and the method reliability is validated by standard addition recovery experiments in real water and rice samples. Furthermore, the Mn-TCPP nanozyme is embedded into an agarose hydrogel matrix, enabling visual, instrument-free monitoring of Cu²⁺ contamination: increasing Cu²⁺ concentrations induce a discernible fluorescence color transition from orange to yellow under 365 nm illumination. This work presents a tunable MOF platform that exploits competitive targets synchronous modulation of fluorescence and enzyme-mimicking activity, providing a robust, selective, and field-deployable ratiometric sensor for Cu²⁺.

PMID:
42456258
Bibliographic data and abstract were imported from PubMed on 16 Jul 2026.

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