Surface Conductivity of Biological Macromolecules Measured by Nanopipette Dielectrophoresis

Abstract

We report the measurement of the surface conductivity of biological macromolecules by dielectrophoretic trapping at the tip of a glass nanopipet. We find that the threshold voltage for trapping is a function of salt concentration and can be directly linked to the effective conductivity of the biomolecule and its solvation shell. The surface conductivities obtained for 20-mer single-stranded DNA, 40-mer double-stranded DNA, and yellow fluorescent protein are $7.9\pm 1.9\mathrm{nS}$, $5.3\pm 0.7\mathrm{nS}$, and $21.5\pm 1.6\mathrm{nS}$, respectively.