A water-soluble polyfluorene derivative PFBTM-NMe3+ bearing mannose as well as quaternary ammonium groups on side chains is designed and synthesized via click chemistry and Suzuki cross-coupling polymerization. The conjugated glycopolymer PFBTM-NMe3+ displayed excellent solubility in polar solvents with absolute photoluminescence quantum yield (Φ) of 4.1% and 13.4% in water and methanol, respectively. Owing to the low doping of benzothiadiazole (BT) moieties along the backbone, PFBTM-NMe3+ exhibited weak interchain Förster resonance energy transfer (FRET) in water. After binding with Gram-negative bacteria, E. coli that possess net negative charge and bunch of mannose binding lectins FimH on the surface, PFBTM-NMe3+ showed strong FRET and ratiometric response owing to interchain polymer aggregation. Interestingly, Gram-positive bacteria (S. aureus) and fungi (C. albicans) did not present similar substantial response due to the absence of lectin proteins and less net negative charge on the surface. Moreover, confocal microscopy indicates that bacteria undergo aggregation after binding with PFBTM-NMe3+ within 2 min and could be proficiently discriminate from fungi even in a mixed condition via fluorescence imaging technique, which facilitate the potential of this method for realistic use. Hence, by simply balancing the synergistic effect of electrostatic and carbohydrate-protein interactions between polymer PFBTM-NMe3+ and microbes, the selective recognition and imaging of bacteria over fungi could be achieved within a very short period of time without employing any complicated procedures.
Keywords: FRET; bioimaging; biosensors; click chemistry; conjugated polymers; ratiometric.