Weighing single molecules with light

Scientists at Oxford University have developed a light-based measuring technique that could transform our ability to characterise 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. Senior author Professor Philipp Kukura, from Oxford's Department of Chemistry, said: 'This 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.' The researchers first demonstrated the use of light scattering to visualise 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. Professor Kukura said: 'We then addressed the question of whether we could use our visualisation approach to quantify, rather than just detect, single molecules.