The electrochemical biosensor was prepared by modification of a glassy carbon electrode (GCE) with Au nanoparticles (AuNPs), G-quadruplex DNA (G(4)DNA) and i-motif DNA (C(4)DNA or i-DNA) structures to investigate of telomerase enzyme inhibitors. SH-G(4)DNA and SH-i-DNA were linked to the modified electrode by AuNPs-S binding. This platform was used to study the quadruplex DNA/ligand interaction. The interaction of different ligands with quadruplex DNA was studied in a 5.0 mM [Fe(CN)(6)](3 - /4 -) solution as a redox probe at the surface of these biosensors, using the electrochemical impedance spectroscopy (EIS) technique. The resistance of charge transfer (R-ct) values was increased by increasing the concentration of ligand due to the quadruplex DNA/ligand interaction. Under the optimum conditions, the observations revealed that 1,4-dihydropyridine (1,4-DHP) derivatives had a good affinity toward the quadruplex DNA structures in the concentration range of 5.0-700.0 mu M. The selectivity was examined using different double-stranded (ds-DNA) sequences.