Scientists have developed a light-based measuring technique that could transform our ability to characterize biomolecules.

Using a microscope that detects light scattering rather than fluorescence, the researchers have demonstrated that single molecules can be observed, and their mass measured, in solution, is reported in the journal Science.

'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.'

The researchers first demonstrated the use of light scattering to visualize individual proteins - biomolecules only a few nanometres across - in 2014. But it was not until last year that they were able to improve the image quality sufficiently to compete with fluorescence.

The senior author said: '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.'

Using interferometric scattering microscopy to quantify the mass of single biomolecules in solution with 2% sequence mass accuracy, up to 19-kilodalton resolution, and 1-kilodalton precision. We resolved oligomeric distributions at high dynamic range, detected small-molecule binding, and mass-imaged proteins with associated lipids and sugars. These capabilities enabled us to characterize the molecular dynamics of processes as diverse as glycoprotein cross-linking, amyloidogenic protein aggregation, and actin polymerization.

It is this generality that excites the authors. The co-author of the work, 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.'

The researchers say the technique - which they call interferometric scattering mass spectrometry (iSCAMS) - could have applications ranging from studies of protein-protein interactions to drug discovery and even point-of-care diagnostics.

Because essentially every physiological and pathological process is controlled by biomolecular interactions in solution, the researchers say this technology has considerable potential impact. The team is in the process of commercializing the technology to provide access to other researchers who are not experts or may not even use optical microscopy. The researchers say: 'It has the potential, we think, to revolutionise how we study biomolecul es and their interactions.'

http://www.ox.ac.uk/news/2018-04-27-weighing-single-molecules-light

http://science.sciencemag.org/content/360/6387/423