Synthesis and Characterization of a Cationic BODIPY-Conjugated Polymer as a Fluorescent Probe for Bacterial Sensing

The incidence of infections caused by resistant pathogens has been steadily increasing. In this context, the accurate detection of microorganisms is essential to optimize antimicrobial therapy. This approach enables a rapid response to infections, reduces the indiscriminate use of antimicrobials, and allows for efficient treatment monitoring. Therefore, the development of fluorophores capable of detecting pathogens represents a promising strategy for the diagnosis and control of resistant infections. In this work, 8-pentafluorophenyl-1,3,5,7-tetramethyl pyrromethene fluoroborate (BDP) was synthesized from pentafluorobenzaldehyde and 2,4-dimethylpyrrole in dichloromethane, catalyzed by trifluoroacetic acid. The mixture was then treated with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as an oxidizing agent. After 6 h, triethylamine and boron trifluoride diethyl etherate were added to close the dipyrromethene ring, yielding BDP (14%). The conjugation of BDP to polyethylenimine (PEI) was carried out by stirring at room temperature for 72 h. At the end of the reaction, TLC analysis showed complete consumption of the starting BDP, with the resulting conjugate (BDP-PEI) remaining at the origin of the chromatographic plate. The UV-visible absorption spectra of these compounds in N,N-dimethylformamide showed a main absorption band around 505 nm. The fluorescence emission band at 515 nm was assigned to the 0-0 vibrational band of the S₁→S₀ electronic transition. Fluorescence quantum yields of 0.98 and 0.18 were obtained for BDP and BDP-PEI, respectively. Furthermore, BDP-PEI exhibited strong green fluorescence emission in Staphylococcus aureus cells, indicating its potential application as a fluorophore for pathogen sensing.