Figure 1.

Ion-selective single-walled carbon nanotube-based biomimetic devices. Structural comparison of (a) a biological ion channel with (b) a small-diameter single-walled carbon nanotube. The ionic conductance through both nanochannels is strongly affected by the presence of fixed charges and/or electronegative groups on the pore through an electrostatic mechanism. (a) Side view of the potassium channel MthK (PDB ID: 1LNQ).¹⁹ A ring of eight negative charges is formed at the entrance of the intracellular vestibule of CaK channels, which increases the local concentration of K⁺.²⁰ (b) Model representation of a (10,0) carbon nanotube with a ring of carboxyl groups (oxygen atoms shown in red) present at the channel entrance. The residues along the K-channel and the entrance of the SWCNT are colored for a better view. (c) Schematic of the SWCNT devices studied here. Ionic current–voltage measurements were performed across the two fluidic reservoirs patterned in a PMMA resist through two Ag/AgCl electrodes. The two fluidic reservoirs are connected through the interior of one carbon nanotube (1.5 ± 0.4 nm on average diameter and 20 μm in length) laying on the surface of the Si/SiO₂ substrate. Images are not drawn to scale.