The modification of graphene oxide (GO) onto the surfaces of chemically activated pencil graphite electrodes (PGEs) was performed herein, and then these electrodes were applied for the first time on voltammetric monitoring of miRNAs. The specific recognition of miRNA-34a, which has been related to Alzheimer disease, was explored in the presence of DNA-RNA hybridization by using CA/GO/PGEs in combination with differential pulse voltammetry (DPV) technique. The characterization of CA/GO/PGE was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The effect of GO concentration, DNA probe concentration and miRNA-34a concentration upon to biosensor response was optimized, and accordingly, the selectivity of miRNA-34a biosensor was tested under the optimum conditions. (C) 2017 Elsevier B.V. All rights reserved.