An electroless deposition method of depositing metal nanoparticles onto conductive substrates such as carbon nanotubes is provided. The carbon nanotubes are provided on a support comprising a metal substrate and then immersed in an aqueous solution containing metal ions. The metal substrate metal has a redox potential which is lower than that of the metal ions in solution such that the metal ions are readily reduced into metal nanoparticles on the carbon nanotubes.