Some embodiments provide methods and systems for creating ladder/standards as quality control tools for length-based separation of carbon nanotubes; determining the length purity; or measuring distribution of lengths of a collection of carbon nanotubes. Some embodiments further provide methods and systems for dispersing carbon nanotubes by conjugation of the carbon nanotubes with biomolecule moieties, specifically proteins. Further, some embodiments provide an indicator for length-based separation of carbon nanotubes via conjugation of one or more biomolecules onto the surfaces of the nanotubes. In some embodiments, such a method can include conjugating a biomolecule to the carbon nanotubes and subjecting the conjugated carbon nanotubes to silver-stained gel electrophoresis to separate the conjugated carbon nanotubes based on their lengths.