Charge-tunable hemicyanine probes for bacterial imaging and bacterial infection tracking.

We developed a series of charge-tunable near-infrared hemicyanine probes (CNOEM, 1 + OEM, and 2 + OEM). By adjusting the number of positive charges (0 to 2), these probes achieved selective identification and fluorescence imaging of bacteria. The photophysical characterization studies and theoretical calculations revealed a clear structure-activity relationship between the charge distribution/polarity of the probes and their affinity toward bacterial membrane components. The probes exhibited excellent photostability and low cytotoxicity, offering distinct advantages for long-term bioimaging and enabling real-time tracking of bacterial invasion into host cells. In addition, the probes demonstrated stable fluorescence in complex biological fluids (urine and blood) for up to 5 hours. This study provides valuable molecular probe tools for elucidating bacterial infection mechanisms and advancing related clinical diagnostics.