Feldman Alina K, Steigerwald Michael L, Guo Xuefeng, Nuckolls Colin
Department of Chemistry and the Columbia University Center for Electronics of Molecular Nanostructures, Columbia University, New York, New York 10027, USA.
Acc Chem Res. 2008 Dec;41(12):1731-41. doi: 10.1021/ar8000266.
As the top-down fabrication techniques for silicon-based electronic materials have reached the scale of molecular lengths, researchers have been investigating nanostructured materials to build electronics from individual molecules. Researchers have directed extensive experimental and theoretical efforts toward building functional optoelectronic devices using individual organic molecules and fabricating metal-molecule junctions. Although this method has many advantages, its limitations lead to large disagreement between experimental and theoretical results. This Account describes a new method to create molecular electronic devices, covalently bridging a gap in a single-walled carbon nanotube (SWNT) with an electrically functional molecule. First, we introduce a molecular-scale gap into a nanotube by precise oxidative cutting through a lithographic mask. Now functionalized with carboxylic acids, the ends of the cleaved carbon nanotubes are reconnected with conjugated diamines to give robust diamides. The molecular electronic devices prepared in this fashion can withstand and respond to large environmental changes based on the functional groups in the molecules. For example, with oligoanilines as the molecular bridge, the conductance of the device is sensitive to pH. Similarly, using diarylethylenes as the bridge provides devices that can reversibly switch between conjugated and nonconjugated states. The molecular bridge can perform the dual task of carrying electrical current and sensing/recognition through biological events such as protein/substrate binding and DNA hybridization. The devices based on DNA can measure the difference in electrical properties of complementary and mismatched strands. A well-matched duplex DNA 15-mer in the gap exhibits a 300-fold lower resistance than a duplex with a GT or CA mismatch. This system provides an ultrasensitive way to detect single-nucleotide polymorphisms at the individual molecule level. Restriction enzymes can cleave certain cDNA strands assembled between the SWNT electrodes; therefore, these strands maintain their native conformation when bridging the ends of the SWNTs. This methodology for creating novel molecular circuits forges both literal and figurative connections between chemistry, physics, materials science, and biology and promises a new generation of integrated multifunctional sensors and devices.
由于硅基电子材料的自上而下制造技术已达到分子长度尺度，研究人员一直在研究纳米结构材料，以便从单个分子构建电子产品。研究人员已投入大量实验和理论工作，致力于使用单个有机分子构建功能性光电器件以及制造金属 - 分子结。尽管这种方法有许多优点，但其局限性导致实验结果与理论结果之间存在很大分歧。本综述介绍了一种创建分子电子器件的新方法，即用电功能性分子共价连接单壁碳纳米管（SWNT）中的间隙。首先，我们通过光刻掩膜进行精确的氧化切割，在纳米管中引入分子尺度的间隙。现在，裂解后的碳纳米管末端用羧酸官能化，再与共轭二胺重新连接，形成稳定的二酰胺。以这种方式制备的分子电子器件能够基于分子中的官能团承受并响应较大的环境变化。例如，以寡苯胺作为分子桥时，器件的电导对pH敏感。同样，使用二芳基乙烯作为桥可提供能在共轭态和非共轭态之间可逆切换的器件。分子桥可以执行双重任务，即传导电流以及通过诸如蛋白质/底物结合和DNA杂交等生物事件进行传感/识别。基于DNA的器件可以测量互补链和错配链的电学性质差异。间隙中一条匹配良好的15聚体双链DNA的电阻比带有GT或CA错配的双链低300倍。该系统提供了一种在单个分子水平检测单核苷酸多态性的超灵敏方法。限制性内切酶可以切割组装在SWNT电极之间的某些cDNA链；因此，这些链在桥接SWNT末端时保持其天然构象。这种创建新型分子电路的方法在化学、物理、材料科学和生物学之间建立了实际和形象的联系，并有望带来新一代集成多功能传感器和器件。
