A facile strategy for photoactive nanocellulose-based antimicrobial materials

The prolonged survival of microbes on surfaces in high-traffic/high-contact environments drives the need for a more consistent and passive form of surface sterilization, with the goal of minimizing pathogen transmission. Here, we developed self-disinfecting materials through the covalent attachment of a porphyrin-based photosensitizer (PS) to nanofibrillated cellulose (NFC) and paper (Pap), imparting antimicrobial activity to these renewable scaffolds via photodynamically generated singlet oxygen. The facile covalent attachment of the free-base 5-(4-aminophenyl)-10,15,20-tris-(4-N-methylpyridinium)porphyrin (A₃B³⁺) and metallated [5-(4-aminophenyl)-10,15,20-tris-(4-N-methylpyridinium)porphyrinato]zinc(ii) (Zn-A₃B³⁺) photosensitizers was accomplished by aqueous cyanuric chloride coupling, avoiding the use of organic solvents of previous coupling strategies, while preventing PS leaching that is an issue with non-covalent PS incorportation strategies. Materials characterization and the degree of photosensitizer loading were determined by FTIR, elemental and TGA analyses, and UV-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS). The antimicrobial potencies of the resultant PS-NFC and PS-Pap materials were evaluated against four strains of bacteria recognized by the World Health Organization as either critical or high priority pathogens: Gram-positive strains methicillin-resistant S. aureus (MRSA; ATCC-44) and vancomycin-resistant E. faecium (VRE; ATCC-2320), and Gram-negative strains multidrug-resistant A. baumannii (MDRAB; ATCC-1605) and NDM-1 positive K. pneumoniae (KP; ATCC-2146). Our results demonstrated broad photodynamic inactivation of all strains studied upon illumination (30 min; 65 ± 5 mW cm⁻²; 400–700 nm) by a minimum of 99.999%. Antiviral studies against two enveloped viruses, dengue-1 (DENV) and vesicular stomatitis virus (VSV), revealed complete inactivation by both materials. Taken together, the results demonstrate the potential for photoactive NFC as the basis for sustainable broad spectrum anti-infective materials.