Newly Constructed NiCo₂O₄ Derived from ZIF-67 with Dual Mimic Enzyme Properties for Colorimetric Detection of Biomolecules and Metal Ions

Integration of novel bio-/nanostructures as effective sensing platforms is still of great significance for robust and rapid analysis. Herein, a novel metal-organic framework-derived NiCo₂O₄ was synthesized via a feasible templating method. Significantly, redox couples of both Ni³⁺/Ni²⁺ and Co³⁺/Co²⁺ provided richer oxidation-reduction reactions, thereby leading to an enhanced catalytic activity. Furthermore, NiCo₂O₄ as an enzyme mimic with peroxidase-like activity and oxidase-like activity could oxidize colorless thylbenzidine (TMB) to blue oxTMB in the absence of H₂O₂. Thus, a sensitive chromogenic sensing platform for detecting Fe²⁺, thiourea, cysteine (Cys), and epigallocatechin-3-gallate (EGCG) was proposed. The colorimetric detection methods exhibited great features of low limit of detection (LOD) and broad linear range. Owing to the complexation reaction, the chromogenic sensing system of TMB + NiCo₂O₄ + Cys achieved effective detection of Cu²⁺ and Mn²⁺ with the LODs of 0.0022 and 0.0181 mM, respectively. Developed detection methods with wide linear ranges of 0.008-0.1 mM for Cu²⁺ and 0.08-1 mM for Mn²⁺ had excellent practical potential. Similarly, the reaction system of TMB + NiCo₂O₄ + EGCG could achieve the colorimetric detection of Cu²⁺ and Fe³⁺. The great chromogenic sensing performance for detecting Cu²⁺ and Fe³⁺ with a broad linear range and a low LOD could be also realized.