Electron-Transfer Gated Ion Transport in Carbon Nanopipets

Coating the inner wall of a quartz nanopipet with a thin layer of carbon yields a nanopore with tunable surface charge and chemical state for resistive-pulse and rectification sensing. Herein we report the experimental study and modeling of the electron-transfer gated ion transport processes in carbon nanopipets. The potential of the unbiased carbon layer can be tuned by adding very low (sub-nM) concentrations of redox species to the solution via bipolar electrochemistry. The potential of the carbon layer determines the electrical double-layer structure that, in turn, affects the ionic transport processes. The ion current rectification decreased when redox species with a relatively positive formal potential (e.g., Fe(CN)₆^3/4-) were added to the solution and increased upon adding redox species with a negative formal potential (e.g., Ru(NH₃)₆^3/2+). Additionally, the ion current displays high sensitivity to redox species, suggesting the possibility of trace-level analysis.