The indicator-based nucleic acid detection protocol is one of the major approaches to monitor the sequence selective nucleic acid hybridization-mediated recognition events in biochemical analysis. The metal complex, cobalt phenanthroline, [Co(phen)(3)(3+)], which is one of the electroactive indicators, interacts more with double stranded nucleic acids via intercalation. Thus, this interaction permits an increase at the electrochemical signal of [Co(phen)(3)(3+)]. In our study, the interaction of metal complex, [Co(phen)(3)(3+)] with nucleic acids was examined using pencil graphite electrodes (PGEs) in combination with differential pulse voltammetry (DPV) technique. The voltammetric detection of miRNA-34a was investigated based on the changes at the electrochemical signal of [Co(phen)(3)(3+)] under optimized experimental conditions; such as accumulation potentialof metal complex and DNA probe concentration, hybridization time, target miRNA concentration. Furthermore, the selectivity of electrochemical miRNA-34a biosensor was studied in contrast to different miRNAs. The applicability of indicator-based biosensor specific to miRNA-34a was also presented by using total RNA samples. (C) 2020 Elsevier B.V. All rights reserved.