An enzyme-encapsulated MOF@MOF nanocomposite for detecting H₂O₂ derived from superoxide anion released by mitochondria of HeLa cells

In this work, a horseradish peroxidase (HRP)-encapsulated metal organic framework (MOF)@MOF nanocomposite is developed for detecting H₂O₂ converted by dismutation of superoxide anions released from live HeLa mitochondria. Initially, an HRP-polyacrylic acid cluster is incorporated on a mesoporous, peroxidase-like Cu/Co-1,4-benzenedicarboxylate (BDC) MOF platform to avoid structural change and deactivation of HRP through its interactions with MOF metal ions. Additionally, a Cu/Co-BDC(HRP)@1,3,5-benzenetricarboxyate (BTC) core-shell MOF/MOF structure, also with peroxide-like properties, serves as a protective matrix for HRP. Then, ultrathin porous carbon shells (UPCS) are adopted to improve the electrical conductivity of the MOF@MOF. The Cu/Co-BDC(HRP)@BTC|UPCS sensing platform exhibits two linear ranges of 0.05–1 µM and 1–1000 µM with a sensitivity of 172 mA mM⁻¹ cm⁻² and 1.63 mA mM⁻¹ cm⁻², respectively. A limit of detection of 0.057 µM, good selectivity and stability over 35 days for H₂O₂ detection are also achieved. After treating the mitochondrial complex with specific inhibitors, amperometric results at the sensing platform confirmed complex I and III within mitochondria as the main electron leakage sites in the electron transfer chains. Therefore, this sensing platform provides a tool that may aid in predicting and even developing treatments for some oxidative stress diseases caused by mitochondrial abnormalities.