Single-biomolecule Sensing Based on Molecular Conductance Measurements

Recently, there have been significant advances in analytical methodologies to explore electronic properties of a single molecule. The conductance in electron transport through a single molecule (single-molecule conductance) can be reliably and reproducibly measured by scanning tunneling microscopy (STM). The single-molecule conductance strongly reflects the chemical structure of a sample molecule, and, therefore, can be utilized for sensing application. Indeed, the conductance measurements allow, for example, sensing of a metal ion or environmental pH measurements on a single-molecule basis. Furthermore, molecular STM tips, prepared by chemical modification of metal tips, open up a novel way to quantify electron transfer from a single molecule to an adjoining single molecule. Such measurements enable highly selective detection of a biomolecule. A molecular tip having molecular recognition ability undergoes the formation of a supramolecular assembly with the target biomolecule. Detecting the electron transfer through the assembly leads to the single-molecule detection.