Functional Nanozymes Consisting of Co²⁺-ZIF-67 Metal-Organic Framework Nanoparticles and Co²⁺-ZIF-67/Polyaniline Conjugates

Co²⁺-ZIF-67 metal-organic framework nanoparticles (NMOFs), act as nanozymes catalyzing diverse processes, including peroxidase, oxidase, and catalase activities. Peroxidase activities are reflected by the nanozyme-catalyzed H₂O₂ oxidation of dopamine to aminochrome, the H₂O₂ oxidation of NADH to NAD⁺, the H₂O₂-catalyzed generation of chemiluminescence through oxidation of luminol, and the H₂O₂-mediated oxidation of aniline to polyaniline. Oxidase activities of the nanozyme are demonstrated by the Co²⁺-ZIF-67 NMOFs catalyzed aerobic oxidation of dopamine to aminochrome and of NADH to NAD⁺, and catalase activities of the nanozyme are reflected by the catalytic decomposition of H₂O₂. Moreover, the Co²⁺-ZIF-67 catalyzed oxidation of aniline to polyaniline (PAN) by H₂O₂ is accompanied by the coating of NMOFs with PAN to yield a Co²⁺-ZIF-67/PAN hybrid material. Coating the particles in the presence of guest substrates leads to molecular imprinted PAN matrices revealing enhanced ZIF-67 catalyzed transformations as compared to non-imprinted PAN matrices. This is demonstrated by imprinting of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS²⁻, in the PAN coating and the 3.3-fold enhanced catalyzed oxidation of ABTS²⁻ by H₂O₂, as compared to the non-imprinted PAN hybrid composite. Moreover, imprinting of L-/D-DOPA in the PAN coating of Co²⁺-ZIF-67 NMOFs leads to chiro-selective H₂O₂-guided oxidation of L-/D-DOPA to dopachrome by the NMOFs/PAN composite.