US Patent 7479325 - Isotope doped carbon nanotube

http://www.freepatentsonline.com/7479325.html

Isotopic labeling is a method for tracking a sample during chemical processing. This patent from Tsinghua University teaches an isotope doped carbon nanotube useful for such labeling. Claim 1 reads:

1. An isotope-doped nanotube of an element, comprising:

an elongated tube structure including a first nanotube segment made of first isotopes of said element, and a second nanotube segment made of second isotopes of said element, the first and second nanotube segments selectively occurring along an axial direction of said elongated tube structure.