"Single-molecule imaging has been recognized as one of the most powerful techniques to characterize molecular motions and interactions in wide ranges of microscopically heterogeneous systems in life and materials science," said Satoshi Habuchi, KAUST Associate Professor of Bioscience.

In a paper published recently in Nature Communications, Prof. Habuchi, postdoctoral fellow Dr. Maged Serag and Ph.D. student Maram Abadi from KAUST's Biological and Environmental Science and Engineering Division outline how they developed a new single-molecule imagining method that allows for simultaneous characterization of size, shape and conformational dynamics of individual molecules, along with an accurate determination of their diffusion kinetics.

Powerful Molecule-tracking Method Redefined

For over 30 years, single-molecule localization and tracking (SMLT) has been one of the best ways to characterize the motion of individual molecules. Scientists use it to examine cells at the subcellular level (for example, to characterize cell receptors), and also use it to better understand the properties of polymers used in materials processing and fabrication.

"The characterization of these processes is essential in both the fundamental sciences and in industrial applications," said Prof. Habuchi. However, SMLT does not provide information about the shape and size of individual molecules or of molecular conformational dynamics, has different limitations in data analysis, can be inefficient and does not always work.

Because of these issues, the researchers focused on developing a new multi-parametric single-molecule imaging method. "It provides a unique opportunity to simultaneously characterize these fundamental physical properties," said Prof. Habuchi.

Development of the Cumulative-Area Method

The new method relies on the characterization of cumulative area occupied by the molecules, and is called the cumulative-area (CA) method. The researchers used micrometer-sized DNA molecules as model systems, and showed that the CA method worked for a wide range of nano- and micro-sized objects ranging from nanoparticles to macromolecules.

"The CA method gave quantitative information about the size, diffusion coefficient and conformational relaxation time of the individual molecules we examined," Prof. Habuchi said. "We believe it will provide a platform for multidisciplinary research, and it expands the capability of molecule imaging techniques to a wider spectrum of research areas."

For example, Prof. Habuchi pointed out that the CA method could be used to study polymer dynamics in physics, and could also be employed to examine the molecular mechanism of the spatial organization of chromatin in a cell.

"The life sciences and materials science field are the research fields where single-molecule imaging techniques can play a major role. In particular, if researchers are examining molecular motion and structural dynamics, our method can serve as a powerful tool," Prof. Habuchi explained.

The researchers noted they were surprised that no one had come up with the idea of the CA method before. "Our method is elegant but also very simple," said paper first author Dr. Serag. "After obtaining all of the simulated data, we were convinced we'd found something very important."

The Way Forward

"The development of new molecular imaging techniques and methods is becoming increasingly important in modern scientific research, as understanding on a molecular level is key for many cutting-edge research areas," noted Prof. Habuchi.

"Indeed, new scientific findings and the development of new materials are often based on new molecular imaging techniques," he continued. "As this area continues to grow in the future, we believe our new imaging method will offer researchers a better way to conduct their research at the molecular level."

- by Caitlin Clark, KAUST News