鎳離子螯合去氧核醣核酸之電性研究及其應用

Abstract

去氧核醣核酸 (DNA) 為自然界中一維的奈米線，其獨特的自組裝性常被應用於生物感測器，以及奈米導線模版的製作。然而其不佳的電導特性，則限制了 DNA 在分子元件發展與應用的潛能。在本研究中，我們將二價鎳離子於鹼性環境下，參雜入 DNA 分子的雙股螺旋中，形成 nickel DNA (Ni-DNA)。並藉由導電掃描探針顯微鏡，及電化學分析結果可知，Ni-DNA 的導電度較原本的 DNA 有大幅的改善。其電荷可能藉由Ni-DNA中，具有良好堆疊之鹼基對間的交互作用來作傳輸，而參雜在其中的鎳離子猶如存在於 DNA 分子中的電洞，使得電子更容易利用電子跳躍 (Electron hopping) 來做電荷的傳輸，並且在鹼基上電子最高填滿軌域 (HOMO) 與最低未填滿軌域 (LUMO) 之間的能隙也因鎳離子的參雜而降低。並且由電化學的分析中可知，DNA 分子中鹼基對的堆疊，對於電荷於 Ni-DNA 中的傳輸有顯著的影響。當鹼基對的堆疊產生變化時 (例如在序列中鹼基對發生錯誤配對，即造成 □ 軌域堆疊的扭曲)，即使得電荷於 Ni-DNA 中的傳輸受到阻礙而呈現出較高的電阻值。藉由電荷於 Ni-DNA 中的傳輸特性，我們成功的將 Ni-DNA 導入至 DNA 生物感測器上的應用。對於 DNA 分子 序列中是否有鹼基對錯誤配對的情況，可以有效的檢測。並對於單一核□酸多型性(single nucleotide polymorphisms; SNPs) 的檢測提供了一個新的方向。 除此之外，Ni-DNA 還可以應用於固態的奈米電子元件上。在本研究中，我們將Ni-DNA 架於兩電極上，並經由電性量測的結果可知，參雜於 Ni-DNA 中的鎳離子會因電位的變化而產生氧化還原反應，此反應會使得 Ni-DNA 的電性上表現出負微分電阻的特性 (Negative differential resistance，NDR)。因此 Ni-DNA 具有極佳的電性分子元件之應用性。

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 nickel ions (Ni2+) are incorporated into the base pairs of DNA at pH ≧ 8.5 and nickel DNA (Ni-DNA) is formed. Meanwhile, electrochemical analyses by cyclic voltammetry and AC impedance show that the conductances of Ni-DNAs are better than that of native DNA by a factor of approximately 20 folds. UV spectroscopy and DNA base pair mismatch analyses of Ni-DNA show that electrons hoping through the □□□ stacking of DNA base pairs may play a vital role for charge transport within Ni-DNA molecules. Meanwhile, the change in resistance that is caused by the mismatched of DNA can also be monitored by electrochemical. In this study, resistance increased exponentially with the number of mismatches. Accordingly, an intuitive and direct method for evaluating the numbers of DNA mismatches can possibly be achieved. Additionally, the exponential increase in the electrical resistance of mismatched Ni-DNA maybe caused by electron tunneling through the mismatch-induced potential barrier in Ni-DNA. In addition, a molecular device that is composed of Ni-DNA molecules exhibits a negative differential resistance (NDR) behavior. When two gold electrodes were connected by Ni2+-chelated DNA (Ni-DNA) molecules which were converted from □-DNA, not only the conductivity of DNA molecules were improved, but also an NDR device was formed at room temperature, in an ambient environment. Such NDR characteristics of a Ni-DNA device may have been caused by the redox reactions of Ni ions. This finding provides a highly potential for constructing electrical nano-devices from biological molecules. This biomaterial is a unique and designable one-dimensional bio-polymer for usage in biosensiors and nanodevices.