Optical microscopy enables single-molecule motion capture

July 25, 2014

A team of researchers has achieved single-molecule imaging and manipulation with optical microscopy using a bead probe as a marker, unveiling fundamental properties such as direction of motion, step size, and the force the molecule exerts, which cannot be resolved by whole-molecule measurements.

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A team of researchers at the University of Tokyo in Japan has achieved single-molecule imaging and manipulation with optical microscopy using a bead probe as a marker, unveiling fundamental properties such as direction of motion, step size, and the force the molecule exerts, which cannot be resolved by whole-molecule measurements.

Single-molecule motion capturing could also become a powerful tool to develop "synthetic" molecular machines. However, it is difficult to apply the conventional method to individual molecules because the size of a typical synthetic molecular machine is only 1 nm--about one-tenth the size of a biomolecular machine. This miniaturization of the target molecule causes significant problems such as low efficiency of the bead probe immobilization reaction and undesired interaction between the surfaces of the bead and substrate.

Prof. Hiroyuki Noji, Dr. Tomohiro Ikeda, and Takahiro Tsukahara at the Department of Applied Chemistry in the Graduate School of Engineering; Professor Ryota Iino at the Okazaki Institute for Integrative Bioscience/Institute for Molecular Science at the National Institutes of Natural Sciences; and Prof. Masayuki Takeuchi in the Organic Materials Group of the Polymer Materials Unit at the National Institute for Materials Science captured the motion of a single synthetic machine about 1 nm in size. In this experiment, the researchers resolved the problems in the conventional method, which are caused by the small size of the target, and visualized the rotational motion of a single double-decker porphyrin (DD), known as a synthetic molecular bearing, by imaging a bead on DD. The researchers also manipulated the motion of the single DD molecule by applying an external force to the bead.

Schematic illustration for single-molecule motion capturing and manipulation of a 1-nm-sized synthetic molecular machine by optical microscopy using a bead probe. A large bead attached to the rotor part of the synthetic molecular bearing (double-decker porphyrin) traces its motion. (Image courtesy of Tomohiro Ikeda)

The method, which allows "seeing and touching" single synthetic molecular machines, provides a strategy to verify and evaluate the performance of synthetic molecular motors generating force, one of the ultimate goals in the development of synthetic molecular machines. For example, if it were possible to create a light-driven synthetic molecular motor connected to a biomolecular motor, it should then be possible to establish a tailor-made energy conversion system that can control various chemical reactions by application of light. Therefore, the method will contribute to establishment of tailor-made energy conversion systems based on molecular machines.

This work was supported by Core Research for Evolutional Science and Technology (CREST) of the Japan Science and Technology Agency.

Full details of the researchers' work appear in the journal Angewandte Chemie International Edition; for more information, please visit http://dx.doi.org/10.1002/anie.201403091.

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