Amorphous carbon nitride a-CN0.26 thin films were elaborated on transparent and conductive glass/indium-tin oxide (ITO) wafers to improve the electroanalytical detection of transthyretin peptide (PN) and specific amino acids (AA) from its sequence, which constitutes a great challenge for the diagnosis of transthyretin-related familial amyloïd polyneuropathy (ATTR). The naphthalene-2,3-dicarboxyaldehyde (NDA) label was used for the derivatization reaction of PN and AAs to form N-2-substituted-1-cyanobenz-[f]-isoindole derivatives (CBI) which are both fluorescent and electroactive. The results obtained on a-CN0.26 were compared with those observed on glassy carbon (GC) as a reference material. It was shown that a soft anodic pre-treatment protocol on glass/ITO/a-CN0.26 electrode in a KCl aqueous solution drastically improved the performances of the CBI-PN and CBI-AA oxidation peak. The oxidation peak potential for all CBI derivatives varied in the same range than those measured on GC and pre-treated glass/ITO/a-CN0.26, while no discrimination could be obtained on as-grown glass/ITO/a-CN0.26 electrodes. For almost all the tested CBI derivatives, peak areas, full-widths at peak mid-height, peak current density and their standard deviation (SD) values were improved on a pre-treated a-CN0.26 electrode in comparison with GC.