Modulating the radical scavenging/generation ability of light-responsive melanin-like nanoplatforms by ascorbic acid treatment

Redox-active nanomaterials represent powerful tools for therapeutics due to either antioxidant or pro-oxidant behavior that is essential in regulating the reactive oxygen species (ROS) levels in the biological systems. A promising way to design and realize bioinspired versatile redox-active nanoplatforms is offered by melanin polymers, which are widely available hydrophobic pigments made of poly(hydroxy indole) planar structures produced by oxidative polymerization of the monomeric precursors. Melanins can radically change the redox activity as a response to external stimuli such as acidification or light irradiation, thus exhibiting ROS-generating ability. Herein, the design of versatile light-triggered redox-active melanin-based nanoplatforms is proposed through a green photocatalytic/solvothermal approach. Extensive physicochemical characterization and radical scavenging assays are conducted to define the main properties of such nanomaterials. They exert a significant paramagnetic behavior together with a strong radical scavenging activity benefitting from post-reduction with ascorbic acid, due to increase in the colloidal stability at high concentrations. ROS generation by 2D melanin-based biointerfaces obtained by depositing thin layers on glass slides is activated by IR and UV light irradiation but quenched after redox exchange with ascorbic acid. This study contributes to the future development of sustainable light-responsive bioelectronic devices.