DNA is a one-dimensional nanowire in nature, and it may not be used in nanodevices due to its low conductivity. In order to improve the conducting property of DNA, divalent Ni(2+) are incorporated into the base pairs of DNA at pH≥8.5 and nickel DNA (Ni-DNA) is formed. Conducting scanning probe microscopy (SPM) analysis reveals that the Ni-DNA is a semiconducting biopolymer and the Schottky barrier of Ni-DNA reduces to 2 eV. Meanwhile, electrochemical analysis by cyclic voltammetry and AC impedance shows that the conductance of Ni-DNA is better than that of native DNA by a factor of approximately 20-fold. UV spectroscopy and DNA base pair mismatch analyses show that the conducting mechanism of Ni-DNA is due to electrons hopping through the π-π stacking of DNA base pairs. This biomaterial is a designable one-dimensional semiconducting polymer for usage in nanodevices.

The mechanism underlying DNA charge transport is intriguing. However, poor conductivity of DNA makes it difficult to detect DNA charge transport. Metallic DNA (M-DNA) has better conducting properties than native DNA. Ni(2+) may chelate in DNA and thus enhance DNA conductivity. On the basis of this finding, it is possible to reveal the mechanisms underlying DNA charge transport. The conductivity of various Ni-DNA species such as single-stranded, full complement, or mismatched sequence molecules was systematically tested with ultraviolet absorption and electrical or chemical methods. The results showed that the conductivity of single-stranded Ni-DNA (Ni-ssDNA) was similar to that of a native DNA duplex. Moreover, the resistance of Ni-DNA with a single basepair mismatch was significantly higher than that of fully complementary Ni-DNA duplexes. The resistance also increased exponentially as the number of mismatched basepairs increased linearly after the tunneling current behavior predicted by the Simmons model. In conclusion, the charges in Ni(2+)-doped DNA are transported through the Ni(2+)-mediated π-π stacking corridor. Furthermore, Ni-DNA acts as a conducting wire and exhibits a tunneling barrier when basepair mismatches occur. This property may be useful in detecting single basepair mismatches.

The enterovirus 71 (EV71) has threatened Taiwan for more than ten years. Since traditional diagnostic methods are complicated, time consuming, and high-qualified personnel required. Therefore, a new detection process is highly desired. In this study, a high sensitive PC-based electrochemical analyzing system with a functionalized nano-gold modified immunological electrode are developed to detect EV71. Immobilizing specific EV71 polyclone antibodies, which is developed by center for disease control (CDC) Taiwan, onto nano gold of sensing electrode, the affinity interaction of the immobilized antibody with the specific antigen is identified quickly by electrochemical impedance spectrum (EIS) within 20 minutes. The detection limit of this EIS analysis was as low as 50 copy per ml (∼sub-atto molar). In summary, a biosensor and analyzing system based on EIS has been developed to identify EV71 with efficiency, high sensitivity and specificity.