Photodynamic Microbial Defense of Cotton Fabric with 4-Amino-1,8-naphthalimide-Labeled PAMAM Dendrimer

The article describes the interaction between 4-amino-1,8-naphthalic anhydride and the terminal amine groups of the first-generation poly(amidoamine) (PAMAM) dendrimer. Cotton fabric was treated with the newly obtained photoactive dendrimer (DA) to achieve its antimicrobial photodynamic inactivation. The photodynamic inactivation method is an innovative approach in which, upon irradiation with visible light, photosensitizers generate highly reactive oxygen species, specifically singlet oxygen (¹O₂), which destroys microbial cells. In the dark, the DA dendrimer strongly inhibits the development of the model bacteria Bacillus cereus (a Gram-positive bacterium) and Pseudomonas aeruginosa (a Gram-negative bacterium) in solution. Upon irradiation with visible light, the inhibition is significantly enhanced, achieving almost complete inactivation of <i>B. cereus</i> and 94% of <i>P. aeruginosa</i>. Cotton fabric was treated with the DA dendrimer at two concentrations (0.15% and 0.30% weight of fabric). It was found that the dendrimer molecules are adherent to the cellulose fiber surfaces and do not leach in washing. Treatment of the fabric with DA partially increases its hydrophobicity, which prevents the adhesion of some bacteria. In the dark, the treated fabric shows weak antibacterial activity because the dendrimer DA molecules are attached to the textile surface, and inactivation depends solely on the microorganism's surface contact. However, upon irradiation, a significant increase in the fabric's antimicrobial activity is observed, as the fixed dendrimer participates in the release of singlet oxygen, which effectively attacks microorganism cell membranes and components. For the fabric with the higher concentration (DA30), 94% inactivation of <i>B. cereus</i> and 89% inactivation of <i>P. aeruginosa</i> were achieved. Thus, a synergistic effect between photodynamic activity and increased hydrophobicity was achieved, making the modified cotton fabric an example of a high-tech textile with permanent, renewable disinfection.