Biological Nanopore Probe: Probing of Viscous Solutions in a Confined Nanospace

This paper describes a nanospace probing system constructed with a pore-forming toxin and a hairpin DNA (hpDNA) molecule. The single hpDNA molecule can be inserted and can move in the confined nanospace of the alpha-hemolysin (αHL) pore. The molecular motion of the hpDNA can be determined based on the fluctuation of the blocking current via channel current measurements. Using this system, we investigated the effect of viscosity of the aqueous solution in the macrospace (bulk) and in the confined nanospace with a small molecule (glycerol) and a polymer (PEG600). The molecular motion of the hpDNA in the nanospace differed in glycerol and PEG600 solutions, while the viscosity remained the same in the bulk solution. The fundamental factors for the viscosity in glycerol and PEG600 solutions are hydrogen bonding and the entanglement of polymer chains, respectively. This difference in factors becomes significant in confined nanospaces, and our system allows us to observe its effect. Additionally, we constructed a spatially resolved nanopore probe integrated into a gold nanoneedle. The αHL–hpDNA nanoprobe system was constructed with the nanoneedle and can be used to monitor the nanospace with nanometer spatial resolution.