In one aspect, the present invention is generally directed to methods for measuring distribution of lengths of a collection of carbon nanotubes. In particular, the present teachings provide an indicator for length-based separation of carbon nanotubes (CNTs) via conjugation of one or more biomolecules onto the surfaces of the nanotubes. As discussed in more detail below, in some embodiments, such a method can include conjugating a biomolecule to the carbon nanotubes and subject the conjugated carbon nanotubes to silver-stained gel electrophoresis to separate the conjugated carbon nanotubes based on their lengths.