The First NanoSquare Conference of Nanoscience and Nanotechnology Single Molecule Analyses by Molecular Tips for Scanning Tunneling Microscopy

Understanding electron transport through a single molecule is of fundamental importance for molecular electronics. Recently, there have been significant advances in the measurement of electron transport through a single molecule [1]. One of the next challenges toward the realization of molecular electronic devices lies in measuring electron transport between single molecules interacting with each other. Such a measurement is necessary because a self-assembly technique, in which chemical interactions is utilized to organize molecules, is a promising approach to the fabrication of functional nanostructures. We have developed molecular tips for scanning tunneling microscopy (STM). The molecular tips are prepared by chemical modification, typically via chemisorption of organosulfur compounds, of conventional metal STM tips. We demonstrated that such functionalization enables recognition of chemical identities of a single molecule [2]. Besides, the molecular tips offer a unique means to detect the electron transfer between single molecules [3]. In the present study, we show quantification of the electron transfer through a hydrogen bond between single molecules. We found that a hydrogen bond conducts electrons better than a covalent σ bond at short range. Moreover, we utilized the transport property of a single DNA molecule as a fingerprint to achieve single-molecule detection of DNA. Single-stranded DNA was utilized as a probe tip for single-molecule DNA detection. Hybridization of the DNA tip and target DNA induce electron tunneling through the resulting DNA duplex. It is demonstrated that the DNA tip allows not only genetic detection but also discovery of single-nucleotide polymorphism at the single-molecule level.