Biomimetic CuO/ZTF-8 nanozyme-based neoteric sensor for the selective detection of superoxide anions

Abstract

Superoxide (O₂˙⁻) is a short-lived oxygen intermediate and an inevitable member of the reactive oxygen species, which has been found to participate in several physiological and pathological processes. O₂˙⁻ is also well known as a biomarker, as its abnormal levels can lead to tumours and cancers, making its dynamic detection crucial for pathological studies, health screening and early diagnosis of diseases. The rational design of metal–organic frameworks with enzymatic functions has gained increasing interest due to their structural robustness and ability to judiciously introduce numerous active sites into nanosized particles. Herein, for the first time, we have designed and developed a novel copper oxide nanoparticle-embedded zeolitic tetrazolate framework (CuO/ZTF-8) as an enzymatic mimic for the bimetallic enzyme copper–zinc superoxide dismutase (Cu–Zn SOD) and explored its efficacy for the electrochemical detection of O₂˙⁻. The constructed sensor displayed linearity for O₂˙⁻ detection in two concentration ranges of 25 μM to 350 μM and 350 μM to 2.475 mM, achieving a very low limit of detection of 6.19 μM. The CuO/ZTF-8 demonstrated SOD-like activity due to its structural similarity with natural Cu–Zn SOD and abundant copper active sites. This is also the first-ever report on exploring the ZTF-8 framework through a post-modification approach to accomplish enzyme-mimic activity. The firm anchoring of CuONPs into the ZTF-8 architecture afforded excellent cyclic and long-term stability to the fabricated sensor.