NANOPORE DETECTION of LONG TIME-SCALE SINGLE METALLIC CLUSTER CONFORMATIONAL CHANGES and SURFACE LIGAND EXCHANGE

Single molecule nanopore spectroscopy serves as an emerging tool for studying small molecules in aqueous environments without the need for additional chemical labels. Recently it has been seeing increased use as a tool for investigating small metallic nanoparticles and clusters. These clusters consist of a handful of metallic atoms (e.g. Au18) and are regularly ‘passivated’ with organic ligands to provide functionality and protect against aggregation. There has been a widening gap in research studying the surface kinetics of these passivating ligands at the single molecule level as well as during the exchange process. In this work we investigated these surface kinetics using nanopore spectroscopy, which revealed a number of unique properties and kinetics. By trapping small metallic clusters (approx. 2 nm in diameter) in the sensing region of a biological nanopore and studying the resulting current blockade we were able to elucidate quantized discrete state transitions occurring on relatively long time scales (10 ms \u3c t \u3c 10s) dependent on capping ligand mass. We attributed this behavior to reorganization of the ligand surface. We then showcase how this technique can monitor single ligand exchange reactions within the nanopore and use the previously discovered quantized state transitions to identify number and type of ligand exchange occurring. Finally, we reveal that the nanopore can detect different isomers of Mercaptobenzoic Acid (MBA) ligands capping a gold metallic cluster, and we show that differences in their previously mentioned quantized state structures are due to weak interactions