Impedance characteristics of amine modified single glass nanopores.

Mass transport through an interfacial area at nanometer scale is a key process to be addressed in research and applications employing nanostructured electrodes, nanofluidic devices, and high surface area materials. Ionic transport through single glass nanopores is investigated by multifrequency impedance techniques. The conical glass nanopores display current rectification under controlled experimental conditions in voltammetric studies. Being inaccessible by conductivity and DC voltammetry, phase sensitive capacitive and "inductive" components in the two-dimensional impedance spectrum reveal dynamic ionic transport information. The nanopore impedance responses are strongly influenced by the concentration of electrolytes and are correlated with current rectification. Multitime-constant impedance loops are detected in different frequency ranges. The multitime-constant features are attributed to the negative charges at the glass-solution interface. The impedance data are interpreted by designed equivalent circuit models. With the correlation of experimental and modeling results established, current signals can be differentiated into two categories: those originated from ionic transport affected by the immobilized charges at the solid-solution interface and those resulted from the applied waveform with ionic transport governed by geometric factors such as the radius of the nanopore.