Carbon paste electrodes (CPEs) modified by the addition of amino-functionalized multiwalled carbon nanotube/electroactive polyimide (AF–MWCNT/EPI) composites (AF–MWCNT/EPI-CPE) have been prepared and applied to the electrochemical sensing of ascorbic acid (AA). First, MWCNTs were grafted with 4-aminobenzoic acid in a medium of polyphosphoric acid/phosphorus pentoxide to obtain MWCNTs functionalized with 4-aminobenzoyl groups (AF–MWCNTs). The amino functional groups on the AF–MWCNTs reacted with an oligoaniline by oxidative coupling polymerization to yield the AF–MWCNT/EPI composites. Fourier transform infrared spectra and Ultraviolet-Visible absorption spectra revealed that the quinoid rings present on the EPI graft interacted with the AF–MWCNTs. Cyclic voltammetry studies indicated improved electrochemical properties of the AF–MWCNT/EPI composites, demonstrating the occurrence of efficient electron/charge transfer between the AF–MWCNTs and the EPI graft. The concentration of the added AA and the change in the peak current obtained showed a linear relationship. In addition, the calibration curve of the amperometric response of the AF–MWCNT/EPI-CPE sensors against the concentration of AA was also linear. The detection limit and the sensitivity of the AF–MWCNT/EPI-CPE AA sensors were 4.1 μM at a S/N (signal to noise ratio) of 3 and 27.5 μA mM−1, respectively.
