NOVELTY - A composite comprises a nanotube; a biological moiety non-covalently associated with the nanotube; and a metallic moiety bound to the biological moiety.    USE - As composite useful for making dispersion and articles (claimed) e.g. sensors (e.g. chemical sensors, biosensors, and optical sensors), fuel cells (e.g. proton exchange membrane (PEM) fuel cells and direct methanol fuel cells), electrochemical devices (e.g. transistors and interconnects in electrical circuits), solar cells, and hydrogen storage devices; for preparing supported catalyst or an electrode in the devices.    ADVANTAGE - The composite provides high-density metal-functionalized nanotubes. The method functionalizes carbon nanotubes with metallic moieties while preserving the integrity of the nanotube surface (e.g. no carbon-carbon bonds are broken). The functionalized nanotubes have improved properties, e.g. catalytic activity and/or biological functionality that allow their applications in fields such as alternative energy, biotechnology, catalysis, sensors, and information technology. Because the nanotube does not form covalent bonds with either the binding moiety or the metallic moiety, the integrity of the nanotube surface is preserved, along with the intrinsic optoelectronic properties of the pristine nanotube. Despite the non-covalent functionalization, the resulting composite exhibits strong electronic coupling between the metallic moieties and the nanotube. In addition, the resulting composite can be soluble in aqueous solutions, thus ensuring its processability in potential applications such as alternative energy (e.g. fuel cells), catalysis, biotechnology. The method allows sorting of single-walled carbon nanotube as a function of structure and/or other properties without irreversibly modifying the nanotubes chemically or structurally, and can achieve simultaneous selectivity of diameter and chirality, diameter and electronic type, electronic type and chirality.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) functionalizing a nanotube involving non-covalently associating a biological moiety with a nanotube; and binding a metallic moiety to the biological moiety; and    (2) a dispersion comprising several composites.