Silver Nanoparticle-Modified 2D MOF Nanosheets for Photothermally Enhanced Silver Ion Release Antibacterial Treatment

Recently, two-dimensional (2D) metal-organic framework (MOF) nanosheet-based composites have been extensively investigated as promising materials for biomedical applications, including antibacterial applications. This study reports the synthesis of silver nanoparticle (Ag NP)-modified 2D Zr-ferrocene-MOF (MOF-Ag) nanosheets by growing Ag NPs on 2D MOF nanosheets via light irradiation-induced reduction for photothermally enhanced silver ion (Ag⁺) release antibacterial treatment. The MOF nanosheets were synthesized by a hydrothermal method followed by ultrasonic treatment. Subsequently, Ag NPs were grown on the MOF nanosheets to obtain MOF-Ag nanosheets by in situ light irradiation-induced reduction. Various characterization results, including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS), showed that Ag NPs were successfully loaded onto the surface of the MOF nanosheets. Fourier transform infrared (FTIR) spectroscopy further confirmed the successful modification of the MOF-Ag surface with polyvinylpyrrolidone (PVP). The modification with of PVP not only enhanced the stability of MOF-Ag in solution, but also enhanced its biocompatibility. Under 808 nm near-infrared laser (NIR) irradiation, the MOF nanosheets exhibited good photothermal properties and photothermal conversion efficiency. The temperature increase induced by the photothermal effect accelerates the oxidation of Ag NPs to Ag⁺, and thus MOF-Ag continuously releases silver ions to kill bacteria. It was concluded that PVP-functionalized MOF-Ag (PVP@MOF-Ag) nanosheets have good antibacterial properties using experimental analyses such as bacterial growth curves, relative number of colonies, and morphological changes of bacteria. PVP@MOF-Ag nanosheets not only kills S. aureus but also inhibits E. coli growth more efficiently, exhibiting broad-spectrum bactericidal properties. Additionally, the good photothermal performance of the 2D MOF nanosheets enhanced Ag⁺ release and cell membrane permeability. Ag NPs release Ag⁺ in solution via an oxidation mechanism, and the released Ag⁺ is more likely to enter the bacteria via the cell membrane under light conditions. In bacteria, Ag⁺ induces the generation of endogenous reactive oxygen species to trigger oxidative stress, thus realizing efficient antibacterial performance. Based on the above-mentioned antibacterial mechanism and good in vitro antibacterial properties, the PVP@MOF-Ag nanosheets were used for wound healing in mice. By developing a mouse wound healing model and treating mouse wounds within a week, it was observed that PVP@MOF-Ag nanosheets have a good therapeutic effect and good biosafety during treatment. These results demonstrate that PVP@MOF-Ag nanosheets are an efficient platform for photothermally enhanced Ag⁺ release antibacterial therapy and wound healing.