New Light-Based Measuring Technique Helps Observe Biomolecules

A light-based measuring method that could change the humans’ ability to characterize biomolecules has been developed by researchers at Oxford University.

The scientists used a microscope that detects light scattering, rather than fluorescence, to show that single molecules can be visualized, and their mass can be determined, in solution. The study was performed in association with institutions in Sweden, Germany, the US, and Switzerland and has been reported in the journal Science.

Philipp Kukura, the senior author, and Professor from Oxford's Department of Chemistry said: “research has emerged from a decade of work which involved making an ever more sensitive light microscope.

Single molecules have been observed in light microscopes since the late 1980s, but essentially all optical techniques rely on fluorescence, which is the emission of light by a material after being "excited" by the absorption of electromagnetic radiation. As immensely powerful as that is, it is not universal.”

Earlier in 2014, the scientists first showed how light scattering can be used to observe biomolecules —individual proteins that measure only a few nanometers across. However, it was only last year that they were able to enhance the image quality adequately to contend with fluorescence.

We then addressed the question of whether we could use our visualization approach to quantify, rather than just detect, single molecules. We realized, given that the volume and optical properties of biomolecules scale directly with mass, that our microscope should be mass sensitive. This turned out indeed to be the case, not only for proteins but also for molecules containing lipids and carbohydrates.

Philipp Kukura, Senior Author

This generality is what excites the authors. Professor Justin Benesch of Oxford's Department of Chemistry, co-author of the work and an expert in mass measurement, said: “The beauty of mass is that it is both a universal property of matter and extremely diagnostic of the molecule under investigation. Our approach is therefore broadly applicable and, unlike traditional single-molecule microscopy, does not rely on the addition of labels to make molecules visible.”

According to the researchers, the method, which they have dubbed interferometric scattering mass spectrometry (iSCAMS), could be used in many applications such as drug discovery, studies of protein-protein interactions, and even point-of-care diagnostics.

iSCAMS has lots of advantages. It measures mass with an accuracy close to that of state-of-the-art mass spectrometry, which is expensive and operates in a vacuum - not necessarily representative of biological systems - whereas iSCAMS does so with only a very small volume of sample and works in essentially any aqueous environment.

Philipp Kukura, Senior Author

Professor Benesch added: “This enables a lot of the things that researchers want to quantify: do certain molecules interact and, if yes, how tightly? What is the composition of the protein in terms of how many pieces it contains, and how does it grow or fall apart?”

Since biomolecular interactions in a solution essentially control all pathological and physiological processes, this technology has a major potential impact, say the researchers. Professor Kukura said: “The universal applicability, combined with the fact that the instruments are close to shoebox size, can be operated easily, and allow the user to see the molecules in real time, is tremendously exciting.”

The researchers are in the process of commercializing the technology in order to give access to other teams who are not professionals or may not be using optical microscopy.

It has the potential, we think, to revolutionize how we study biomolecules and their interactions”, say the researchers.

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