A copper(II)/cobalt(II) organic gel with enhanced peroxidase-like activity for fluorometric determination of hydrogen peroxide and glucose

Abstract

A bimetallic organic gel was prepared by mixing the bridging ligand 2,4,6-tri(4-carboxyphenyl)-1,3,5-triazine with Cu(II) and Co(II) ions at room temperature. The resulting metal-organic gel (MOG) shows enhanced peroxidase-like activity, most likely due to the synergetic redox cycling between Co(III)/Co(II) and Cu(II)/Cu(I) pairs. These accelerate interfacial electron transfer and generation of hydroxy radicals. The MOG can catalyze the reaction of H₂O₂ with terephthalic acid (TPA), producing a blue fluorescence product with the maximum excitation/emission at 315/446 nm. The enzyme mimic was used to design a fluorometric method for H₂O₂ that has a 81 nM detection limit. H₂O₂ is also formed by glucose oxidase-assisted oxidation of glucose by oxygen, and an assay for glucose was worked out based on the above method. It has a 0.33 μM detection limit. This study may open up a new avenue to design and synthesize nanomaterial-based biomimetic catalysts with multiple metal synergistically enhanced catalytic activity for potential applications in biocatalysis, bioassays and nano-biomedicine. Graphical abstracts Schematic presentation of the synergic catalytic effect of Cu(II)/Co(II) bimetallic organic gel promoted by the redox cycle between Co(III)/Co(II) and Cu(II)/Cu(I) pairs. The bimetallic organic gel can catalyze the reaction of H₂O₂ with terephthalic acid, thereby producing a blue-fluorescent product.

Keywords: 2-hydroxyterephthalic acid; Catalysis; Enzyme mimic; Fluorescence; Hydroxy radicals; Metal-organic gel; Peroxidase mimetic; Redox cycle; Synergistic effect; Terephthalic acid.