Copper-induced tert-butoxy-substituted terpyridine hydrogel for enhanced peroxidase-like activity and colourimetric glutathione sensing

Abstract

Metal–organic hydrogels (MOHs) have gained prominence as artificial enzymes due to their tunable coordination environments and porous architectures. In particular, copper-based MOHs have exhibited exceptional peroxidase-like activity by mimicking the substrate-binding pockets and redox-active centres of natural enzymes. However, achieving high catalytic efficiency under mild conditions remains a key challenge. Herein, we synthesised a novel tert-butoxy-functionalized terpyridine ligand, 4′-(4-(tert-butoxy)phenyl)-2,2′:6′,2′′-terpyridine (L), and engineered a copper-coordinated hydrogel (CuHG) with hierarchical nanofibrous morphology and robust viscoelasticity. CuHG demonstrated superior peroxidase-like activity at pH 4.0, catalysing the H₂O₂-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). Steady-state kinetic studies revealed its high catalytic efficiency and substrate affinity, with the oxidation mechanism proceeding via Cu²⁺/Cu⁺ redox cycling. By capitalising on the selective inhibition of TMB oxidation by glutathione, we developed a rapid colourimetric biosensor with a detection limit of 1.97 μM and high selectivity over interfering biomolecules. This work provides a blueprint for designing enzyme-mimicking MOHs and expands their utility in environmental remediation and point-of-care diagnostics.