The covalent attachment of acid functionalized multiwalled carbon nanotubes (FMWCNTs) on glassy carbon (GC) electrode using 1,8-octanediamine (OD) as a linker via carbodiimide chemistry was described. The attachment of FMWCNTs on GC electrode were confirmed by attenuated total reflectance Fourier transform infra-red (ATR-FT-IR) spectroscopy, Raman, scanning electron microscopy (SEM) and electrochemical impedance studies. Raman spectrum of FMWCNTs modified surface shows the characteristic G and D bands at 1563 cm(-1) and 1340 cm(-1), respectively. This confirmed the successful attachment of FMWCNTs on the OD modified GC surface. Further, the attachment of FMWCNTs on OD modified surface via amide linkage was confirmed from the observed characteristic peak at 1681 cm(-1) in the ATR-FT-IR spectrum. The SEM images showed that the covalently attached FMWCNTs retained their morphology similar to powder and the average diameter of them was found to be 58 nm. Unlike modification of FMWCNTs on gold substrates with the aid of conventional thiol linkers (Au-S bond), modification of them by the present method was stable for a wide positive potential window due to the robust C-N bond. To demonstrate the electrochemical stability of the MWCNTs modified electrode at more positive potential, guanosine 5'-monophosphate (GMP) was selected as a representative probe because its oxidation occurs at more than 1 V. It was found that the FMWCNTs modified electrode not only showed a stable signal for GMP but also enhanced its oxidation current when compared to bare GC electrode. Further, the present strategy of modifying FMWCNTs was extended to prepare a composite electrode by electrochemically depositing 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) film. The FMWCNTs-polymer composite electrode dramatically enhanced the GMP oxidation current when compared to polymerization of AMT (p-AMT) and FMWCNTs alone. The polymer composite electrode was successfully employed for the sensitive determination of GMP. Using amperometry, a limit of detection of 0.27 mu M ( S/N = 3) was achieved for GMP at a composite modified electrode. (C) 2015 Elsevier Ltd. All rights reserved.