ssDNA Wrapping of Single-Walled Carbon Nanotubes and the Role of Sequence Periodicity: A Critical Review

Noncovalent hybrids of single-stranded DNA (ssDNA) and single-walled carbon nanotubes (SWCNTs) are central to chiral sorting and near-infrared biosensing, yet no quantitative rule connects the periodicity of a natural sequence to the geometry of a given nanotube. Earlier reviews treat the sequence as a tool for sorting or sensing; this critical review asks what the published evidence up to 2026 establishes about periodicity. We compare base–wall affinities from calculation, calorimetry and force spectroscopy; the periods reported by cryo-electron microscopy, scanning tunnelling microscopy, atomic force microscopy (AFM) and X-ray scattering in solution; the recognition sequences used for single-chirality sorting; and the few studies of genomic DNA. The experimental order of base affinities depends on the method and on whether the surface is flat or curved. Helical pitches of 1.6–3.3 nm, spacings of 8.6–14.3 nm between strands in solution and the AFM period of about 14 nm are different quantities. Recognition depends on sequence pattern, length, chiral angle and handedness in addition to diameter. To our knowledge, base spacing at fixed composition has been varied only in covalently cross-linked hybrids; for noncovalent wrapping, this test is still missing. We outline the next experiments and the reporting standards and open data they require.