We report a new technique to characterize poly- oxometalate (POM) structures at micromolar solution concentra- tion using single molecule nanopore-based measurements. The pH-dependent structural changes in phosphotungstic acid deter- mined with this technique were validated with NMR (the na- nopore method is more sensitive by one order of magnitude). Importantly, we also demonstrate that the method can identify [PW9O34]9- structural isomers at the single molecule level. The results suggest that nanopore measurements can serve as a com- plementary approach with enhanced sensitivity to traditional ana- lytical chemistry tools but with enhanced sensitivity. Because of its demonstrated ability to identify POM isomers, other molecular properties with controlled geometrical changes, such as the differ- ent location of a given atom, or a rotation of a fragment of the molecule, could potentially be investigated with this method.
Journal of the American Chemical Society