Anisotropic electric conductivity in an aligned DNA cast film
Anisotropic electric conductivity in an aligned DNA cast film
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DOI：
10.1021/ja980165w
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发表时间：
1998-06-24
影响因子：
15
通讯作者：
Shimomura, M
中科院分区：
文献类型：
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作者：
Okahata, Y;Kobayashi, T;Shimomura, M
脱氧核糖核酸 (DNA) 作为生物信息的重要来源，取决于其碱基序列。 DNA 作为一种分子材料也很有趣，它显示出具有碱基对 (bp) 堆叠的长棒状双链体结构：碱基间距为 3.4 Å，而双链体的直径约为 20 Å。 1 因此，它似乎是沿着堆叠碱基的 π 电子云进行一维能量转移和传导的良好候选者。宏观电导率已通过使用双链 DNA 随机定向的纤维凝胶进行了研究。 2-4 已在均质水溶液中研究了插入 DNA 分子中的氧化还原染料分子之间的光诱导电子转移。 5-7 这些报告鼓励我们制备排列好的 DNA 薄膜作为各向异性导电薄膜，其中反 Na+ 阳离子完全交换为阳离子两亲物。 8 如下制备对齐的DNA膜。 8, 9 将来自鲑鱼睾丸的 DNA 水溶液（平均 MW 1.3×106，约 2000 bp）与阳离子两亲物 N,N,N-三甲基-N-(3,6,9,12-四氧二十二烷基)溴化铵水溶液混合。 8 收集沉淀的 DNA-脂质聚离子复合物（磷酸根阴离子与阳离子两亲物的比例为 1:1）并溶解在氯仿/乙醇（4:1 v/v）中。将溶液(40 mg mL-1, 4 wt%)浇注在聚四氟乙烯板上，并在室温下在饱和溶剂蒸气下缓慢蒸发溶剂。所得自立膜（厚约60μm）透明、柔韧且不溶于水。 DNA薄膜可以在室温下用手拉伸2-3倍。从X射线衍射实验和偏振吸收光谱来看，DNA链沿拉伸方向以41 Å的距离排列，如图1所示。 8, 9 薄膜中DNA碱基对堆叠的距离为3.4 Å，与水溶液中天然DNA的堆叠相似。将拉伸的DNA薄膜（20×10 mm，厚度30（5 µm）放在梳形电极板上，如图1所示2. 10 使用电流表（R8340A，Advantest，Co.，Tokyo）在 25°C 环境气氛下或在真空瓶中在 0.1 mmHg 下测量直流电导率。典型结果如图 2 所示。当将拉伸的 DNA 薄膜放在梳状电极上，DNA 链轴垂直于两个 Au 电极时，观察到大欧姆电流（0-4.1 µA），该电流随着施加电压的增加而线性增加。相反，当DNA链与两个电极平行排列时，即使在0.1V的电压下也几乎观察不到电流（小于0.08nA）。当使用未拉伸的膜时，电流很小。
Deoxyribonucleic acids (DNAs) are important as a source of biological information depending on their base sequences. DNA is also interesting as a molecular material that shows a long rodlike duplex structure with base-pair (bp) stacking: the base separation is 3.4 Å while the diameter of the duplex is about 20 Å. 1 It therefore appears to be a good candidate for onedimensional energy transfer and conduction along the π-electron clouds of stacked bases. Macroscopic electric conductivity has been studied by using fibrous gels in which duplex DNAs are randomly oriented. 2-4 Photoinduced electron transfer between redox dye molecules intercalated in DNA molecules has been studied in homogeneous aqueous solution. 5-7 These reports encouraged us to prepare an aligned DNA film as an anisotropic conductive film, in which counter Na+ cations were exchanged completely to cationic amphiphiles. 8 The aligned DNA film was prepared as follows. 8, 9 An aqueous solution of DNA from Salmon testes (average MW 1.3× 106, ca. 2000 bp) was mixed with an aqueous solution of a cationic amphiphile, N, N, N-trimethyl-N-(3, 6, 9, 12-tetraoxadocosyl) ammonium bromide. 8 The precipitated DNA-lipid polyion complex (1: 1 ratio of phosphate anion to cationic amphiphile) was collected and solubilized in chloroform/ethanol (4: 1 v/v). The solution (40 mg mL-1, 4 wt%) was cast on a Teflon plate, and the solvent was evaporated slowly under saturated solvent vapor at room temperature. The obtained self-standing film (ca. 60 µm thick) was transparent, flexibly strong, and water-insoluble. The DNA film could be stretched 2-3 times in length by hand at room temperature. From X-ray diffraction experiments and polarized absorption spectra, DNA strands were confirmed to be aligned with a distance of 41 Å along the stretching direction as schematically shown in Figure 1. 8, 9 The distance between stacked base-pairs of DNAs in the film was 3.4 Å, similar to native DNA stacking in the aqueous solution.The stretched DNA film (20× 10 mm, thickness 30 (5 µm) was put on a comb-shaped electrode plate as shown in Figure 2. 10 The dc conductivity was measured using an ammeter (R8340A, Advantest, Co., Tokyo) at 25 C in ambient atmosphere or in an evacuated bottle at 0.1 mmHg. Typical results are shown in Figure 2. When the stretched DNA film was put on the combshaped electrode with the DNA strand axis aligned perpendicular to the two Au electrodes, a large ohmic current (0-4.1 µA) was observed that increased linearly with increasing applied voltage up to 0.1 V. On the contrary, when the film was placed with DNA strands aligned parallel to the two electrodes, electric current was hardly observed even at a voltage of 0.1 V (less than 0.08 nA). When the unstretched film was employed, a small current