Fabrication of carbon nanotube membranes attached on a glass capillary for the detection of individual ions

Abstract

We developed a nanopore platform with improved reproducibility in terms of both fabrication and the detection of ionic species, using centimeter-long and horizontally aligned carbon nanotubes having average diameter of 4 nm. Carbon nanotubes were embedded into an epoxy matrix and microtomed with 10 關m thickness, resulting in fabrication of hundreds of carbon nanotube membranes having identical pores. The membrane attached on a glass capillary can be directly used for the measurement of pore-blocking events caused by cations, and switching between different analytes is done simply by dipping the capillary into another solution. The noise level was also reduced by using glass capillaries with smaller inner diameter. This platform allows for the statistical prediction of the threshold voltage for the ions to enter the pores, by recording IV-curves based on repeated voltage-ramping protocol. The threshold voltages for K+, Na+, and Li+ were -90 mV, -30 mV, and -10 mV, respectively. The mobility values estimated from the blocking events at each bias were 7.59 x 10-8 m2/Vs, 3.56 x 10-8 m2/Vs, and 4.95 x 10-9 m2/Vs for K+, Na+, and Li+, respectively, which are lower than the values previously reported from the pores of single-walled carbon nanotubes.