Quaternary ammonium functionalized cationic polythiophene for the detection and imaging of gram-positive bacteria

Abstract

The persistence of bacterial infections in humans causes severe adverse health consequences and uncertainties in the global economy. It is of great advantage to develop a rapid tool for the earlier diagnosis and treatment of pathogenic infections. In this work, an active polythiophene derivative containing reactive pentafluorophenyl (PFP) ester groups was prepared via Fe3+-catalyzed oxidative polymerization using PFP thiophene-3-acetate as the monomer. The active polythiophene derivative was conjugated with N,N-dimethyl-1,3-propanediamine via ester-amine reaction, followed by quaternization with 1-bromobutane. The resultant polythiophene derivative (QPDMAPTA) possesses the quaternary ammonium salt groups on its side chain and shows cationic zeta potential of + 12.79 eV at neutral pH. The as-prepared QPDMAPTA exhibits high-level antibacterial action against gram-positive bacteria (Staphylococcus aureus (S. aureus), Staphylococcus epidermidis (S. epidermidis), and methicillin-resistant S. aureus) as compared with gram-negative bacteria (Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa)). Furthermore, the zeta potential measurements show higher uptake of QPDMAPTA by gram-positive bacteria than the gram-negative bacteria, which depicts the active role of the biological interactions with the charged QPDMAPTA in its differential uptake and bactericidal effect. This phenomenon also facilitates the identification of gram-positive bacteria by observing the color changes of collected bacterial cakes before and after treatment with QPDMAPTA. The fluorescent nature of QPDMAPTA can be used for imaging and detection of gram-positive bacteria via adopting a fluorescent technique.