We successfully prepared the modified M-DNA molecular wires by the insertion of the divalent zinc ions (Zn2+) in every base pair of X-DNA molecules. We found that the current-voltage (I-V) characteristics of M-DNA are distinctively different from those measured using other types of DNA molecules including X-DNA: one of the unique features of the modified M-DNA molecular wires was the metallic property observed in the I-V characteristics (i.e., a linear I-V relationship), suggesting that they might be used to build the metallic nanowire for the future nanodevices. Several parameters such as (1) humidity during the electrical measurement and (2) pH in preparation of M-solution are important factors to decide the I-V characteristics of M-DNA molecular wires. For instance, if the X-DNA molecules were treated with the pH value of less than 8, they did not show the characteristics of metallic M-DNA molecular wires. In addition, the conductivity of M-DNA molecular wires decreases as the measurement pressure moves to the high vacuum range, although the unique feature (i.e., linear relationship) was maintained even at 10(-5) Torr. (c) 2005 Elsevier B.V. All rights reserved.