Coherence Resonance in a Single Walled Carbon Nanotube Ion Channel

Biological signaling networks are able to utilize coherent and oscillatory signals from intrinsically noisy and stochastic components for ultrasensitive discrimination using stochastic resonance, a concept not yet demonstrated in man-made analogs. We show that the longest, highest aspect ratio, and smallest diameter synthetic nanopore examined to date, a 500 μm single walled carbon nanotube (SWNT), approximately 1.5 nm in diameter, demonstrates oscillations in electro-osmotic current at specific ranges of electric field, that are the signatures of coherence resonance, a form of stochastic resonance, yielding self-generated rhythmic and frequency locked signals. SWNT were grown on a SiO₂ wafer and connected between two bonded, aqueous reservoirs at their plasma-etched and open ends. Stochastic pore blocking is observed when individual cations (Na+, Li+, K+, 1 M) partition into the nanotube during electro-osmosis, partially obstructing an otherwise stable proton current. We report the highest recorded proton conductivity experimentally observed (5×10₂ S/cm), suggesting an ordered water phase in the SWNT interior. The observed oscillations in the current occur due to a coupling between stochastic pore blocking and a diffusion limitation that develops at the pore mouth during proton transport. This is the first example of resonant transport in a synthetic nanopore, and illustrates how simple ionic transport can generate coherent waveforms within an inherently noisy environment, and points to new types of nano-reactors, sensors, and nanofluidic channels based on this platform.