Characterizing individual Au 25 (SG) 18 clusters within a nanopore detector

Metallic quantum clusters are stable structures that can exhibit many useful properties. Clusters can be ligand stabilized in aqueous environments to expand their usefulness as biosensors. There are some limitations in characterizing the physical and chemical properties of individual water soluble clusters. This report describes initial results of a new approach for detecting and characterizing individual gold nanoclusters (Au25(SG)18) in an aqueous solution with nanopore-based resistive pulse sensing. Here the nanopore is a single alpha hemolysin from Staphylococcus aureus. Clusters that enter through the cis side of the pore (large vestibule) usually create shallow current blockades with a mean residence time of several milliseconds. Clusters that enter through the trans side of the pore (narrow lumen) create deeper blockades that are either very short (∼200 μs), long lived (∼50 ms) or trapped (>10s). The short and long lived blockades yield sufficient statistics to help characterize the clusters and the trapped state events may allow for additional analysis and controlled delivery of individual clusters. We demonstrate the possibility of this additional analysis by performing I-V measurements on individually trapped clusters. These show an optimal voltage for confining a cluster within the pore.