A comparison of ion channel current blockades caused by individual poly(ethylene glycol) molecules and polyoxometalate nanoclusters.

Proteinaceous nanometer-scale pores have been used to detect and physically characterize many different types of analytes at the single-molecule limit. The method is based on the ability to measure the transient reduction in the ionic channel conductance caused by molecules that partition into the pore. The distribution of blockade depth amplitudes and residence times of the analytes in the pore are used to physically and chemically characterize them. Here we compare the current blockade events caused by flexible linear polymers of ethylene glycol (PEGs) and structurally well-defined tungsten polyoxymetallate nanoparticles in the nanopores formed by Staphylococcus aureusα-hemolysin and Aeromonas hydrophila aerolysin. Surprisingly, the variance in the ionic current blockade depth values for the relatively rigid metallic nanoparticles is much greater than that for the flexible PEGs, possibly because of multiple charged states of the polyoxymetallate clusters.