High-resolution discrimination of homologous and isomeric proteinogenic amino acids in nanopore sensors with ultrashort single-walled carbon nanotubes.

The hollow and tubular structure of single-walled carbon nanotubes (SWCNTs) makes them ideal candidates for making nanopores. However, the heterogeneity of SWCNTs hinders the fabrication of robust and reproducible carbon-based nanopore sensors. Here we develop a modified density gradient ultracentrifugation approach to separate ultrashort (≈5-10 nm) SWCNTs with a narrow conductance range and construct high-resolution nanopore sensors with those tubes inserted in lipid bilayers. By conducting ionic current recordings and fluorescent imaging of Ca flux through different nanopores, we prove that the ion mobilities in SWCNT nanopores are 3-5 times higher than the bulk mobility. Furthermore, we employ SWCNT nanopores to discriminate homologue or isomeric proteinogenic amino acids, which are challenging tasks for other nanopore sensors. These successes, coupled with the building of SWCNT nanopore arrays, may constitute a crucial part of the recently burgeoning protein sequencing technologies.