Recently, Lee et al fabricated single-walled CNT ion channels with negatively charged ends ~1.5 nm in diameter that conduct protons and are blocked by cations present in the surrounding electrolyte solution. Moreover, they observe complete rejection of ions for voltages b100 mV. Once the electric field is large enough the larger cations move across the channel, and this blocks the flow of protons. These synthetic nanopores are therefore capable of single-ion detection