Cu(II)–Inosine Supramolecular Gel with Nanofibrous Morphology as Laccase and Peroxidase Mimic for Optical Sensing Applications

The formation of supramolecular metal–organic gels using biomolecules as organic counterparts is essential considering the tedious and time-consuming steps required in designing ligands that can interact with metal ions to form a gel. A supramolecular metal–organic gel based on a simple nucleoside, inosine, and Cu²⁺ ions using coordination-driven self-assembly is reported in this work. The coordination interaction between Cu²⁺ ions and inosine in the presence of NaOH resulted in the generation of a stable and self-standing supramolecular metal–organic hydrogel. The Cu–inosine gel demonstrates a number of useful characteristics, including thixotropy, stimuli responsiveness, and self-healing. Further, the metal–organic gel exhibited excellent ability to mimic the laccase and peroxidase enzymes even under harsh conditions such as elevated temperature, varying pH, and ionic strengths. The laccase-like activity of the metallogel has been utilized for the oxidation of several phenolic compounds and the detection of epinephrine and dopamine colorimetrically, with a detection limit of 0.039 and 0.027 μM, respectively. Further, the peroxidase mimetic ability of the Cu–inosine gel has been successfully utilized for the visual sensing of glutathione with a limit of detection of 0.047 μM. The limits of detection for all three biomolecules are better than or comparable to most literature reports. It is expected that the use of organic–inorganic hybrid nanostructures such as the metallogels constructed using benign biological building blocks as artificial enzymes will open up possibilities in applications such as environmental remediation and biosensing.