Universal Scaling of Robust Thermal Hot Spot and Ionic Current Enhancement by Focused Ohmic Heating in a Conic Nanopore

Abstract

A stable nanoscale thermal hot spot, with temperature approaching 100 °C, is shown to be sustained by localized Ohmic heating of a focused electric field at the tip of a slender conic nanopore. The self-similar (length-independent) conic geometry allows us to match the singular heat source at the tip to the singular radial heat loss from the slender cone to obtain a self-similar steady temperature profile along the cone and the resulting ionic current conductance enhancement due to viscosity reduction. The universal scaling, which depends only on a single dimensionless parameter Z, collapses the measured conductance data and computed temperature profiles in ion-track conic nanopores and conic nanopipettes. The collapsed numerical data reveal universal values for the hot-spot location and temperature in an aqueous electrolyte.

AC electrohydrodynamic Landau–Squire flows around a conducting nanotip

“…Next, we consider the linearized heat conduction equation (4.5 c ) subject to Joule heating: Similar to the study on a Joule-heated slender conic nanopore (Pan et al. 2016), slender body theory implies that and thus the conduction term in (4.10) is dominated by the radial part . Together with , we solve (4.10) in the approximate form: with the boundary condition T = T w at R = b ( z ).…”

Solid-state nanopore hydrodynamics and transport

“…6). Pan et al 84 also used the large Ohmic heating at the tip of the conic nanopore to elevate the tip temperature to beyond boiling point such that nucleation of FIG. 4.…”

“…First at Peking University and then at Notre Dame, Wang has developed a modified asymmetric etching method to fabricate single asymmetric nanopores suitable for single biomolecule detection. 84,121 He was the first to develop an Atomic Layer Deposition (ALD) method applicable for sub-10 nm asymmetric polymer nanopore surface modification, which significantly improved the biosensing capability of solid-state nanopores. 122 The polymer substrate and the high-permittivity monolayer focus the field through the peripheral monolayer at the tip, such that molecules can be pinned by the leaking field at the tip edge to prolong their translocation time.…”