Triple threat bismuth peptide imaging in cells

Bismuth peptides are emerging as a novel class of pharmaceutical agents. While cell-penetrating bismuth peptides have been reported recently, their detailed cellular interactions and stability remain poorly understood, and therefore new methods are required to visualise these peptides within cells. In this study, we synthesised cell-penetrating bismuth peptides conjugated to various fluorescent dyes (naphthalimide, coumarin, rhodamine B) and their brominated analogues, and investigated their cellular uptake in SKOV-3 cells using X-ray fluorescence microscopy (XFM) for bismuth and bromine, alongside optical fluorescence microscopy. Co-localisation of bromine, bismuth and the fluorescent dyes within the cytosol and cellular compartments indicates that the bismuth-peptide conjugates can enter cells intact. Among the three fluorescent dyes tested, naphthalimide and its brominated derivative were the most robust for multimodal imaging.