A “Light-up” 1D supramolecular nanoprobe for silver ions based on assembly of pyrene-labeled peptide amphiphiles: cell-imaging and antimicrobial activity

Abstract

We prepared pyrene-labeled peptide amphiphiles (PAs) consisting of a hydrophobic linear- or branched-alkyl chain (for 1 or 2, respectively) and a hydrophilic histidine-rich peptide of HGGGHGHGGGHG (HG12). Both peptides have a strong tendency to form nanofibrils (NFs) in aqueous media. The resulting histidine-coated NFs show a great binding affinity to Cu²⁺ as a fluorescence “light-off” sensor. Interestingly, the emission spectra of the pyrene probe show that the different supramolecular assemblies between 1 and 2 can significantly affect the binding affinity to specific metal ions. In particular, “light-up” fluorescent Ag⁺ detection of NFs of 2 through inhibition of photoinduced electron transfer (PET) was observed even at a low concentration of PA solution. As a means to determine the biological responsibility of 2 to Ag⁺, intracellular detection using the “turn-on” response was performed. A considerable enhancement of fluorescence in NF-loaded HeLa cells was observed. In addition, the NFs were used as a template scaffold for the production of Ag nanoparticles (AgNPs) with high monodispersity and stability. The NFs decorated with AgNPs are shown to possess highly effective and long-term antibacterial activity against both Gram-negative and -positive bacteria.