A simple, sensitive and label-free electrochemical sensor is developed for detection of Hg2+ based on the strong and stable T-Hg2+-T mismatches. In the presence of Mg2+, the parallel G-quadruplex structures could be specifically recognized and precipitated in parallel conformation. Therefore, the guanine nanowire was generated on the electrode surface, triggering the electrochemical H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). In this research, a new method of signal amplification for the quantitative detection of Hg2+ was described based on the direct growth of guanine nanowire via guanine nanowire. Under optimum conditions, Hg2+ was detected in the range of 100 pM-100 nM, and the detection limit is 33 pM. Compared to the traditional single G-quadruplex label unit, this electrochemical sensor showed high sensitivity and selectivity for detecting Hg2+. (C) 2016 Elsevier B.V. All rights reserved.