Fluorophore-tagged poly(ʟ-Lysine) block copolymer nano-assemblies for real-time visualization and antimicrobial activity

Abstract

Development of self-reporting polymers having dual-action of membrane disruption for antimicrobial activity and simultaneous visualization and quantification by microscopic imaging techniques are urgently required for early detection and therapeutics. Here, we report a new series of self-reporting coumarin fluorophore-tagged polypeptides based on PEG-block-poly(ʟ-lysine) copolymers via ring opening polymerization (ROP) strategy. For this purpose, NHC catalyzed controlled ROP was optimised for ε-Cbz-ʟ-lysine NCA monomer to make desired chain length polypeptides. The resultant cationic polymer was self-assembled into 100 ± 15 nm nanoparticles (NP) having Zeta potentials of +25 to +44 mV associated with strong blue-emission in aqueous medium. The antimicrobial action of these polymers was tested in E. coli by colony suspension method and their MIC90 values were obtained to be 1 × 10−4 to 3 × 10−4 g/mL. Real-time confocal microscopic imaging enabled the direct visualization of the fluorescent peptide NP action on the E. coli membrane, and propidium iodide co-staining assay further established the membrane pore formation mechanism for their antimicrobial activity. In vitro cytotoxicity and cellular uptake studies in MCF-7 breast cancer cell lines revealed that the fluorescent polypeptide NP were readily internalized at the cellular level, and they were also found to be nontoxic to cells up to 80 μg/mL and showed minimal haemolysis to RBCs at their MIC concentration which further established their high biocompatibility as suitable biomaterials.