Figure 1

Voltages at transition to dielectrophoretic confinement for the 20-mer ssDNA molecules labeled with Rhodamine Green as a function of salt and sucrose concentrations in the bath. The black line is the theoretical fit of this data, with parameters $X=27.7\pm 4.8\mathrm{V}$ and ${\sigma }_p=30.0\pm 4.6\mathrm{S}{\mathrm{m}}^{-1}$. For all measurements, the transition voltage recorded was defined to be that at which fluorescence from macromolecules confined to the tip region was first observable above the background noise of the CCD camera.Reuse & Permissions

Figure 2

Variation of electrokinetic forces on negatively charged macromolecules along the nanopipet tip axis, for applied bath electrode voltages below (left-hand panel)—and just above (right-hand panel)—the transition to trapping. The force versus distance curves (EP: electrophoretic DEP: dielectrophoretic NET: net force) are derived from a simulation of the electric field distribution due to conduction around a nanopipet tip, assuming that the glass itself is a perfect insulator as in [4], and that the surface of the glass is much more conductive tangentially than the surrounding solution, on account of the ions attracted to it. The scale of the $y$ axis is representative, chosen to match the order of magnitude of DEP force estimates made from Eq. (1), and EP force estimates for an effective charge of $e/80$. To convert to the scale of the $z$ components of the electric field, $E$, (in $\mathrm{V}/\mathrm{m}$) or $\nabla (E^2)$ (in ${\mathrm{V}}^2/{\mathrm{m}}^3$), multiply the EP, DEP curves by ${10}^6$, ${10}^{19}$, respectively.Reuse & Permissions