Biodegradable Polypeptide-based Vesicles with Intrinsic Blue Fluorescence for Antibacterial Visualization

Fluorescence imaging has been an indispensable tool to provide dynamic information about the localization and quantity of organisms. Meanwhile, due to the intrinsic hollow structure and modularized biofunctionalities, polymer vesicles have been widely applied in biomedical field. However, most polymer vesicles are embedded with organic fluorophores for fluorescence imaging, which have certain drawbacks such as leakage and possible cytotoxicity. Here, we present a biodegradable polypeptide-based vesicle with intrinsic blue fluorescence without introducing any fluorophore for real-time visualization of antibacterial process. Through modular design to integrate multiple functional fragments, poly( ε -caprolactone)-block-poly(tryptophan)-block-poly(lysine- stat -phenylalanine) [PCL 25 - b -PTrp 2 - b -P(Lys 13 - stat -Phe 4 )] was synthesized, where PCL chains form the hydrophobic membrane, P(Lys- stat -Phe) and PTrp provide intrinsic fluorescence and broad-spectrum antibacterial activity. It is noteworthy that the fluorescence emission was shifted from invisible ultraviolet range of amino acids to visible range (emission maximum at 436 nm), which makes it possible to visualize the antibacterial process. In addition, through utilizing the intrinsic fluorescence of vesicles, confocal fluorescent imaging of vesicles with bacteria validated the specific adhesion of vesicle towards bacteria, and the bacterial death through membrane disruption. Overall, we provided a novel approach to developing biodegradable fluorescent polypeptide-based vesicles for real-time visualization of antibacterial process.