Photoactivated phenothiazine compounds convert sulfur-dyed cellulose fiber fabrics into microbicidal materials

Photoactivated phenothiazines with UV and visible light are converted to radical cations that remain stable for days. Recently, it was discovered that 10H-phenothiazine, when impregnated into natural and synthetic fiber fabrics, imparts antimicrobial properties to these materials. This study, for the first time, investigated the microbicidal properties of an industrial phenothiazine-based dye, sulfur black (SB), which is widely used in the fabric dyeing industry. Fluphenazine (FP), known for its ability to form stable cation radicals, was used as a comparative model. In 100 % cotton fiber fabric (100 C), SB and FP were converted to the corresponding cation radical species, effectively eliminating inoculated coronaviruses and bacteria. In 100 C, FP was more efficient as an antimicrobial agent than SB. Although both compounds generated cation radical species in the fabrics, only FP could produce singlet oxygen. The ability to generate singlet oxygen that can travel over distances contributed to the superior efficacy of FP. Consistently, 100 C treated with FP exhibited greater reactivity with phosphatidylcholine liposomes, a model for biological membranes. Notably, the virucidal activity of FP-treated fabrics persisted even after washing, showing the stability of the antimicrobial effect. MTT assays confirmed that the microbicidal action of FP- and SB-treated fabrics was not due to cytotoxicity, as cell viability remained above the threshold defined by ISO 10993-5. Thus, if microbicidal action is desired, SB-dyed 100 C should be used instead of 100 C. This study contributes to the design of new dye structures that integrate industrial dyeing capacity with effective microbicidal action. Singlet oxygen and free radicals of phenothiazines eliminate virus by membrane disruption. • In fabrics, phenothiazines are photoconverted in situ to free radicals. • Fluphenazine as a model compound compared to the industrial sulfur black dye. • Only fluphenazine exhibited efficient microbicidal action. • Production of singlet oxygen is crucial for microbicidal efficacy. • Microbicidal action involves oxidative damage to lipids.