Metal Organic Framework-Derived Multivariate Flower-Like Cu–Co ₃ O ₄ /CoOOH Nanozymes for Designing Colorimetric Biosensing Metallothioneins

Metallothioneins (MTs) have become important biomarkers for the early clinical diagnosis of malignancies. However, the development of a cost-effective and convenient method for the rapid monitoring of MTs still remains a substantial challenge. Herein, we propose a metal-organic framework (MOF)-derived multivariate flower-like Cu-Co₃O₄/CoOOH nanozyme for the sensitive colorimetric biosensing of MTs. The Cu-Co₃O₄/CoOOH nanozyme was obtained by a novel silica (SiO₂) shell-mediated hierarchical MOF-derived strategy. With the aid of SiO₂ shell, bimetal-based zeolitic imidazolate framework (CuCo-ZIF) was partially pyrolyzed into Cu and Co₃O₄ nanoparticles (NPs), while the remaining Co-ZIF was further transformed into CoOOH nanoflakes through an alkaline etching step. Benefiting from its unique structure, diverse composition, uniform and rich active sites, the synthesized Cu-Co₃O₄/CoOOH nanozyme exhibits greatly enhanced peroxidase (POD)-like activity. In the presence of H₂O₂, the Cu-Co₃O₄/CoOOH nanozyme catalyzes the decomposition of H₂O₂ to generate •OH, which oxidizes 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB. Metallothioneins (MTs), as a type of cysteine-rich protein, can eliminate •OH from the reaction system, and thus a nanozyme-based colorimetric biosensor was constructed for monitoring MTs with a wide linear range (0.035-1.5 × 10³ μM), a low detection limit (2.2 × 10⁻³ μM), excellent specificity, stability, and practicability for serum samples. This work provides a universal and promising hierarchical derivatization of the MOF strategy to design structurally and compositionally diverse nanozymes for biosensing applications.