For the first time, a difference in the structural dynamics of single molecules 1 nm in size at room temperature is observed

The long-standing dream of chemists to observe the structural dynamics of a single molecule is now possible. Single molecules about 1 nanometer in size exist in a volatile state under ambient conditions. Considering that the coronavirus, which is about 100 nm in size, spreads rapidly in the air, it shows how difficult it is to observe a single molecule. Recently, a Korean research team discovered a reliable way to observe single molecules at room temperature by covering them with a thin blanket-like insulating layer.

A research team led by Prof. Kyung-Dak Park and Ph.D. Candidate Mingu Kang (Department of Physics) at POSTECH in collaboration with Prof. Jung Dag Su (Department of Chemistry) of Ulsan National Institute of Science and Technology (UNIST) successfully investigated the conformation (arrangement of atoms in a molecule) of individual molecules at room temperature for the first time, providing a closer look at structural dynamics of a single molecule, which is the basic unit of all substances, including humans.

In-depth analysis using combinational scattering signals, known as molecular fingerprinting, is difficult for molecules exposed to air due to continuous chemical reactions and molecular motions. Ultra-low temperature (below −200 °C) and vacuum conditions are widely used for single-molecule studies to prevent the aforementioned problems, however, the configurations have many limitations in terms of technical difficulties and environmental conditions.

To overcome this, the research team placed a single molecule on a substrate coated with a thin film of gold and covered it with a very thin layer of aluminum oxide (Al₂O₃). The molecule, trapped between layers of gold and aluminum oxide, is isolated from the environment, resulting in the suppression of chemical reactions and molecular movements.

The immobilized molecule is then observed using ultra-sensitive nanoscopy developed by the research team. The use of the method makes it possible to accurately detect weak optical signals of a single molecule thanks to the optical antenna effect of a sharp metal tip. With this, the resolution limit of general optical microscopy (about 500 nm) was overcome to clearly distinguish 1 nm conformational inhomogeneities monomolecules and check whether they stand vertically or lie horizontally.

POSTECH’s Mingu Kang says, “Although the James Webb Space Telescope can observe the farthest point of the observable universe to reveal the origin of the universe, our nanoscopy for one-molecules observes the smallest unit to discover the origin of life.”

The work can reveal the molecular conformation of proteins and DNA at nanometer-level resolution, leading to the discovery of the causes of incurable diseases and the development of treatments for such conditions. In addition, covering the sample a thin layer can be easily applied at room temperature or even higher temperatures for single molecule research and its application.

The study was recently published in Communications of nature.

Courtesy of Phanom University of Science and Technology (POSTECH)