Cu²⁺-Modified Metal–Organic Framework Nanoparticles: A Peroxidase-Mimicking Nanoenzyme

The synthesis and characterization of UiO-type metal–organic framework nanoparticles (NMOFs) composed of Zr⁴⁺ ions bridged by 2,2′-bipyridine-5,5′-dicarboxylic acid ligands and the postmodification of the NMOFs with Cu²⁺ ions are described. The resulting Cu²⁺-modified NMOFs, Cu²⁺-NMOFs, exhibit peroxidase-like catalytic activities reflected by the catalyzed oxidation of Amplex-Red to the fluorescent Resorufin by H₂O₂, the catalyzed oxidation of dopamine to aminochrome by H₂O₂, and the catalyzed generation of chemiluminescence in the presence of luminol/H₂O₂. Also, the Cu²⁺-NMOFs mimic NADH peroxidase functions and catalyze the oxidation of dihydronicotinamide adenine dinucleotide, NADH, to nicotinamide adenine dinucleotide, NAD⁺, in the presence of H₂O₂. The Cu²⁺-NMOFs-catalyzed generation of chemiluminescence in the presence of luminol/H₂O₂ is used to develop a glucose sensor by monitoring the H₂O₂ formed by the aerobic oxidation of glucose to gluconic acid in the presence of glucose oxidase. Furthermore, loading the Cu²⁺-NMOFs with fluorescein and activating the catalyzed generation of chemiluminescence in the presence of luminol/H₂O₂ yield an efficient chemiluminescence resonance energy transfer (CRET) process to the fluorescein reflected by the activation of the fluorescence of the dye (λ = 520 nm, CRET efficiency 35%).