Tuning the ATP-triggered pro-oxidant activity of iron oxide-based nanozyme towards an efficient antibacterial strategy

An alarming increase in bacterial resistance towards various types of antibiotics makes it imperative to design alternate or combinational therapies to treat stubborn bacterial infections. In this perspective, emerging tools like nanozymes, nanomaterials with biological enzyme like characteristics, are being utilised to control infections caused by bacterial pathogens. Among several nanozymes used for antibacterial applications, Fe3O4 nanoparticles (NP) received great attention due to their effective peroxidase like activity. The pH dependent peroxidase activity of Fe3O4 NP results in generation of OH radical via the unique Fenton chemistry of iron. However, their pH dependent activity is restricted to acidic environment and dramatic loss in antibacterial activity is observed at near neutral pH. Here we describe a novel strategy to overcome the pH lacunae of citrate coated Fe3O4 NP by utilizing adenosine triphosphate disodium salt (ATP) as a synergistic agent to accelerate the OH radical production and restore its antibacterial activity over a wide range of pH. This synergistic combination (30 µg/mL Fe3O4 NP and 2.5 mM ATP) shows a high bactericidal activity against both gram positive (B. subtilis) and gram negative (E. coli) bacterial strains, in presence of H2O2, at neutral pH. The synergistic effect (Fe3O4 NP + ATP) is determined from the viability assessment and membrane damage studies and is further confirmed by comparing the concentration of generated OH radicals. Over all, this study illustrates ATP assisted and OH-mediated bactericidal activity of Fe3O4 nanozyme at near neutral pH.