Northwestern University researchers have developed a solution to the double-walled nanotube production problem.

They used a technique called density gradient ultracentrifugation to cleanly and easily separate double-walled nanotubes (DWNTs) from single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).

Double-walled nanotubes enable better electrical conductivity than SWNTs, improved spatial resolution, and longer scanning lifetimes as tips for atomic force microscopes. They are also useful in field-effect transistors, biosensing and drug delivery.