The DNA-thionine-carbon nanotube (DNA-Th-CNT) nanocomposites were prepared by immobilizing DNA on the surface of carbon nanotubes (CNTs) via thionine (Th). The fabrication process was characterized by Raman spectroscopy, UV-vis spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicated that Th could facilitate the immobilization of DNA molecules onto the surface of CNTs, and DNA retained its native secondary conformational structure after it was immobilized. These demonstrated that Th may be served as an effective mediator for immobilization of DNA on CNTs. The nanocomposites were immobilized on the Surface of glassy carbon (GC) electrode forming the DNA-Th-CNTs/GC electrode. The electrode was used to study the interaction between Co(bpy)(3)(3+) probe and the immobilized DNA by cyclic voltammetry, whose results indicated that Co(bpy)(3)(3+) could be electrostatically bound onto the immobilized DNA. The method of the present work has the advantages of rapid and facile CNTs functionalization, high immobilization efficiency. The nanocomposites have a good electrochemical response with a long-term stability, suggesting they have the potential use in the fields of DNA biosensors. (C) 2008 Published by Elsevier B.V.