Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore 117546, Singapore.
J Am Chem Soc. 2021 Dec 8;143(48):20309-20319. doi: 10.1021/jacs.1c09549. Epub 2021 Nov 26.
Deoxyribonucleic acid (DNA) has been hypothesized to act as a molecular wire due to the presence of an extended π-stack between base pairs, but the factors that are detrimental in the mechanism of charge transport (CT) across tunnel junctions with DNA are still unclear. Here we systematically investigate CT across dense DNA monolayers in large-area biomolecular tunnel junctions to determine when intrachain or interchain CT dominates and under which conditions the mechanism of CT becomes thermally activated. In our junctions, double-stranded DNA (dsDNA) is 30-fold more conductive than single-stranded DNA (ssDNA). The main reason for this large change in conductivity is that dsDNA forms ordered monolayers where intrachain tunneling dominates, resulting in high CT rates. By varying the temperature and the length of the DNA fragments in the junctions, which determines the tunneling distance, we reveal a complex interplay between , the length of DNA, and structural order on the mechanism of charge transport. Both the increase in the tunneling distance and the decrease in structural order result in a change in the mechanism of CT from coherent tunneling to incoherent tunneling (hopping). Our results highlight the importance of the interplay between structural order, tunneling distance, and temperature on the CT mechanism across DNA in molecular junctions.
脱氧核糖核酸（DNA）由于碱基对之间存在扩展的π堆积，因此被假设为作为分子导线，但在 DNA 隧道结中电荷传输（CT）机制中有害的因素仍不清楚。在这里，我们系统地研究了在大面积生物分子隧道结中致密 DNA 单层中的 CT，以确定何时是链内或链间 CT 占主导地位，以及在何种条件下 CT 机制变为热激活。在我们的结中，双链 DNA（dsDNA）比单链 DNA（ssDNA）的导电性强 30 倍。这种电导率大幅变化的主要原因是 dsDNA 形成有序的单层，其中链内隧穿占主导地位，从而导致高 CT 速率。通过改变温度和结中 DNA 片段的长度（决定隧穿距离），我们揭示了在电荷输运机制中， 、DNA 长度和结构有序性之间的复杂相互作用。隧穿距离的增加和结构有序性的降低都会导致 CT 机制从相干隧穿变为非相干隧穿（跳跃）。我们的结果强调了在分子结中 DNA 上的结构有序性、隧穿距离和温度对 CT 机制的相互作用的重要性。
