Abstract: Disclosed are methods for separating carbon nanotubes on the basis of a specified parameter, such as length. The methods include labelling of the carbon nanotubes with a biological moiety, followed by SDS-PAGE and staining, to separate the carbon nanotubes on the basis of length and/or characterize their length. In some embodiments, egg-white lysozyme, conjugated covalently onto single-walled carbon nanotubes surfaces using carbodiimide method, followed by SDS-PAGE and visualization of the single-walled nanotubes using silver staining, provides high resolution characterization of length of the single-walled carbon nanotubes. This high precision, inexpensive, rapid and simple separation method obviates the need for centrifugation, additional chemical analyses, and expensive spectroscopic techniques such as Raman spectroscopy to visualize carbon nanotube bands. The disclosed methods find utility in quality-control in the manufacture of carbon nanotubes of specific lengths.