A simple procedure was developed to prepare a glassy carbon electrode modified with carbon nanotubes (CNTs) and thionin. Abrasive immobilization of CNTs on a GC electrode was achieved by gently rubbing the electrode surface on a filter paper supporting carbon nanotubes, then immersing the GC/CNTs-modified electrode into a thionin solution (electroless deposition) for a short period of time (5 – 50 s for MWCNTs and 5 – 120 s for SWCNTs ). Cyclic voltammograms of the resulting modified electrode show stable and a well defined redox couple with surface confined characteristic at wide pH range 2 – 12. The electrochemical reversibility and stability of modified electrode prepared with incorporation of thionin into CNTs film was compared with usual methods for attachment of thionin to electrode surfaces such as electropolymerization and adsorption on the surface of preanodized electrodes. The formal potential of redox couple (E8’) shifts linearly toward the negative direction with increasing solution pH. The surface coverage of thionin immobilized on CNTs glassy carbon electrode was approximately 1.951010 mol cm2 and 3.21010 mol cm2 for MWCNTs and SWCNTs, respectively. The transfer coefficient (a) was calculated to be 0.3 and 0.35 and heterogeneous electron transfer rate constants (Ks) were 65 s1 and 55 s1 for MWCNTs/thionin and SWCNTs/ thionin-modified GC electrodes, respectively. The results clearly show a great facilitation of the electron transfer between thionin and CNTs adsorbed on the electrode surface. Excellent electrochemical reversibility of redox couple, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this procedure for modification of electrodes.
