GSH‐responsive photoactivated nano‐bactericide based on sulfonated sodium alginate for improving photostability and targeting of methylene blue

Abstract

Cationic photosensitizers have higher photodynamic antibacterial activity compared with anionic photosensitizers, and with low toxicity and no drug resistance. However, their poor photostability and low utilization rate limit their practical applications. Herein, a new strategy for the construction of a GSH‐responsive antibacterial nanogel system is developed via the electrostatic interaction between methylene blue (MB) and sulfonated sodium alginate (HSSA) to self‐assemble into nanoparticles followed by sulfhydryl cross‐linking in an aqueous solution. The photobleaching of MB can be inhibited due to the self‐aggregation‐caused quenching (ACQ) effect, but the photodynamic activity can be restored by breaking the disulfide‐crosslinking bonds in the nanogel in response to 10 mM GSH. In vitro antibacterial tests prove that the system has antibacterial activity beyond anionic photosensitizers. Antibacterial studies on plants show that the system has targeted antibacterial activity on infected plants and good wettability, retention, and adhesion to plant leaves. Safety evaluation shows that the system has no obvious toxic effect on plants. Therefore, this study provides a new approach to the discovery of novel photodynamic bactericides.