New strategies for enhanced antibacterial phototherapy properties of FeS2 nanoparticles

In recent years, the increasing prevalence of antibiotic resistance has rendered conventional treatment methods inadequate, thereby intensifying the need for non–antibiotic therapeutic approaches. In this context, phototherapy has emerged as a promising, non–invasive, and targeted treatment. However, the therapeutic efficiency of phototherapeutic agents is considerably dependent on the optical, physical, and surface properties of the materials. Accordingly, semiconductor materials such as iron disulfide FeS2, which are non–toxic, cost–effective, abundant in nature, and capable of broad–spectrum light absorption, offer significant advantages. In this thesis study, two innovative strategies were developed and systematically investigated to enhance the antibacterial phototherapy efficiency of FeS2 nanoparticles. The first strategy involves the construction of a p–n type FeS2/WS2 heterostructure by combining FeS2 nanoparticles with n–type semiconductor tungsten disulfide (WS2) to enhance their photodynamic effect. This heterostructure suppresses the recombination of photo–excited electron–hole pairs and increases the generation of reactive oxygen species (ROS), leading a significant improvement in both photodynamic and photothermal efficiency. The heterostructure containing 30 wt.% WS2 exhibited a photothermal conversion efficiency of 52.6%, and its antibacterial activity with the concentration of 100 μg mL-1 was determined to be 99.4% and 100% against E. coli and S. aureus, respectively The second strategy involves the surface modification of the FeS2 nanoparticles using ε–poly–L–lysine, a cationic and water–soluble biopolymer, to enhance interactions between bacteria and material with reducing agglomeration tendency. The surface modification increased the surface charge of the nanoparticles resulting in improved colloidal stability and strengthened electrostatic interactions with bacteria cells. The modified structures achieved photothermal efficiency of up to 65.5%, exhibited enhanced ROS production, and provided over 99% inactivation of both bacterial species at a material concentration of 125 μg mL-1. The findings demonstrate that both strategies significantly improved the antibacterial phototherapy performance of FeS2 nanoparticles.