Intracellular Delivery and Fate of Peptide-Capped Gold Nanoparticles

Abstract

Gold nanoparticles (NPs) have extraordinary optical properties that make them very attractive single molecule labels. Although understanding their dynamic interactions with biomolecules, living cells and organisms is a prerequisite for their use as in situ sensors or actuators. While recent research has provided indications on the effect of size, shape, and surface properties of NPs on their internalization by living cells, the biochemical fate of NPs after internalization has been essentially unknown. Here we show that peptide-capped gold NPs enter mammalian cells by endocytosis. We demonstrate that the peptide layer is subsequently degraded within the endosomal compartments through peptide cleavage by the ubiquitous endosomal protease cathepsin L. Preservation of the peptide layer integrity and cytosolic delivery of NPs can be achieved by a combination of cathepsin inhibition and endosome disruption. This is demonstrated using a combination of distance-dependant fluorescence unquenching and photothermal heterodyne imaging. These results prove the potential of peptide-capped gold NPs as cellular biosensors. Current efforts focus on in-vivo labeling of NPs, nanoparticle-based real-time sensing of enzyme activity in living cells, and the development of photothermal microscopy for single nanoparticle imaging in living cells.