Resistive-Pulse Nanopore Sensing of Ligand Exchange at the Single Nanocluster Limit for Peptide Detection

Water-soluble metallic nanoclusters require passivating ligands to stabilize and, in many cases, derivatize their surfaces. Recently, we demonstrated the use of resistive-pulse nanopore sensing to observe ligand-induced structural fluctuations of individually trapped nanoclusters. Here we expand on this capability by observing real-time ligand exchange at the single cluster limit. The nanopore technique allows time-resolved observations of ligand exchange and ligand addition with exchange times that agree with calculated free energy profiles. The observed kinetics for thiolated poly(ethylene glycol) (S-PEG) ligands exchanging with tiopronin and glutathione-capped gold clusters is on the order of seconds within the nanoconfined region of the pore, and this rapid exchange motivates the development of a new peptide sensor. We also show proof of concept that nanopore-based exchange between a peptide tiopronin-capped gold cluster leads to current fluctuations that enable identification of the peptide.