A dual-function styryl pyridinium dye platform for targeting bacteria and biofilms

Bacterial infections, especially those involving biofilms and drug-resistant strains, demand integrated diagnostic and therapeutic solutions. Cationic fluorescent molecules, with their imaging and membrane-targeting capabilities, are well-suited for this role. Here, we report alkyl chain-modified styryl pyridinium dyes (1C, 6C, 8C, and 16C) as dual-function agents for bacterial imaging and inhibition. Among them, 8C showed optimal performance, combining strong fluorescence, efficient membrane internalization, and potent antimicrobial activity against <i>E. coli</i> and <i>S. aureus</i>. It disrupted bacterial membranes, as confirmed by NPN uptake, SEM, and zeta potential analyses, and enabled effective visualization of bacterial cells in confocal imaging. 8C also inhibited and disrupted biofilms, showed minimal resistance development under prolonged sub-MIC exposure, and exhibited low mammalian cytotoxicity. These results highlight the potential of alkyl chain engineering in tuning bioactivity and position 8C as a promising theragnostic agent for infectious disease management.