The naphthalene-2,3-dicarboxyaldehyde (NDA) label is widely used for the derivatization of amino acids (AAs) to form N-2-substituted-1-cyanobenz-[f]-isoindole derivatives (CBI) which are both fluorescent and electroactive. [1],[2] Optimal conditions for labeling were previously obtained when [NDA]_tot/[CN^-] ratio =1 and [NDA]_tot /[amino acid or peptide]=40 with a buffer pH of 10. [3],[4] The detection step was achieved by using a carbon reference material (glassy carbon electrode ) exhibiting an obvious oxidation peak for CBI-AA observed at 0.5V/SCE [1]. These experiments confirmed that NDA can by used as a derivative agent for non electroactive AA, allowing for simultaneous electrochemical and fluorescence detections. In this work, amorphous carbon nitride a-CN_0.26 thin films were elaborated on transparent and conductive glass/indium-tin oxide (ITO) wafers to improve the electroanalytical detection of AAs. The results obtained on as-grown a-CN_0.26 were compared to the glassy carbon (GC). It was shown that a soft anodic pre-treatment protocol on glass/ITO/a-CN_0.26 electrode in KCl solution drastically improved the CBI-AA oxidation peak performances. The oxidation peak potential for all CBI derivatives varied in the same range that those on GC and pre-treated glass/ITO/a-CN_0.26, while no discrimination could be obtained for as-grown glass/ITO/a-CN_0.26. For almost all the tested CBI derivatives, the electrochemical properties determined by electrochemical impedance spectroscopy (R_ct, charge transfert resistance) and by differential pulse voltammetry (peak areas, full-widths at peak mid-height, peak current density and their SD values) were improved on pre-treated a-CN_0.26 in comparison with GC.

[1] M. Faure, S. Korchane, I. Le Potier, A. Pallandre, C. Deslouis, A.-M. Haghiri-Gosnet, J. Gamby, Investigating of labeling and detection of transthyretin synthetic peptide derivatized with naphthalene-2,3-dicarboxaldehyde, Talanta, 116 (2013) 8-13.

[2] M. Faure, A. Pallandre, S. Chebil, I. Le Potier, M. Taverna, B. Tribollet, C. Deslouis, A.-M. Haghiri-Gosnet, J. Gamby, Improved electrochemical detection of a transthyretin synthetic peptide in the nanomolar range with a two-electrode system integrated in a glass/PDMS microchip, Lab Chip, 14 (2014) 2800-2805.

[3] S. Korchane, A. Pallandre, C. Przybylski, C. Poas, F. Gonnet, M. Taverna, R. Daniel, I. Le Potier, Derivatization strategies for CE-LIF analysis of biomarkers: Toward a clinical diagnostic of familial transthyretin amyloidosis, Electrophoresis, 35 (2014) 1050-1059.

[4] M. Faure, I. Le Potier, A. Pallandre, S. Chebil, A.-M. Haghiri-Gosnet, C. Deslouis, E. Maisonhaute, J. Gamby, Determination of the isomeric forms proportion of fluorogenic naphthalene-2,3-dicarboxaldehyde in a binary mixture of water:methanol using electrochemical methods, Talanta, 148 (2016) 494-501.