Abstract: Antimicrobial Photodynamic Therapy (aPDT) is an emerging strategy against resistant pathogenic bacteria, a serious global health threat. We describe herein the efficient preparation of photosensitized cellulose nanocrystals (CNC) using trialkoxysilane linkers for covalent incorporation of anionic (Rose Bengal: RB) and cationic (Toluidine blue O: TBO) photosensitizers (PSs), along with a N-alkyl-D-gluconamide ligand to specifically target Escherichia coli, as model nanosystems for aPDT. The synthesized nanomaterials exhibited high PS loading, high singlet oxygen quantum yield comparable to the solution, and good stability in aqueous media with minimal PS release under physiological conditions. Experimental viability tests in bacteria demonstrated their capability for aPDT, mitigating the inherent cytotoxicity of both PSs under dark conditions while retaining high phototoxicity against E. coli bacteria. The presence of gluconamide further enhanced photoactivity, highlighting the importance of surface functionalization with a specific bacterial ligand for improved efficacy. The CNC-supported RB system exhibited sufficient fluorescence for tracking via fluorescence microscopy, making it suitable for theranostics, integrating bioimaging and aPDT. Overall, photosensitized CNCs hold great promise as nanocarriers for combating topical infections caused by Gram-negative bacteria, addressing the urgent need for novel therapeutic strategies in infectious disease management while also mitigating antimicrobial resistance.

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