(361f) High-Yield Analysis of Individual Ions and Molecules through the Interior of Carbon Nanotubes

The interior channels of carbon nanotubes are promising for studying transport of individual molecules in a 1D confined space. However, experimental investigations of the interior transport have been limited by the extremely low yields of fabricated nanochannels and their characterization. Here, this challenge is addressed by assembling nanotube membranes on glass capillaries and employing a voltage-ramping protocol. Centimeter-long carbon nanotubes embedded in an epoxy matrix are sliced to hundreds of 10 μm-thick membranes containing essentially identical nanotubes. The membrane is attached to glass capillaries and dipped into analyte solution. Repeated ramping of the transmembrane voltage gradually increases ion conductance and activates the nanotube ion channels in 90% of the membranes; 33% of the activated membranes exhibit stochastic pore-blocking events caused by cation translocation through the interiors of the nanotubes. Since the membrane-capillary assembly can be handled independently of the analyte solution, fluidic exchange can be carried out simply by dipping the capillary into a solution of another analyte. This capability is demonstrated by sequentially measuring the threshold transmembrane voltages and ion mobilities for K⁺, Na⁺, and Li⁺. Beyond the detection of solvated ions, varying the diameter of carbon nanotubes enables analysis of analytes with different sizes. We show, for instance, detection and identification of individual polymeric molecules with different chain lengths by using a carbon nanotube with diameter of ~3 nm. This approach, validated with carbon nanotubes, will save significant time and effort when preparing and testing a broad range of solid-state nanopores.