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Mass photometry

A new way of characterising biomolecules

Mass photometry is a revolutionary new way to analyse molecules. It enables the accurate mass measurement of single molecules in solution, in their native state and without the need for labels. The ability of mass photometry to yield rapid and intuitive feedback on a variety of applications opens up new possibilities for bioanalytics and research into the functions of biomolecules.

How does it work?

Mass photometry builds on the principles of interference reflection microscopy (1) and interferometric scattering microscopy (2) . Through carefully controlled illumination, a novel spatial-filtering strategy in the detection beam path  (3) and careful image analysis, the group of Prof. Kukura at Oxford University has recently demonstrated that the minute amount of light scattered by single molecules can be reliably detected and, more importantly, that it is directly correlated with molecular mass (Fig 1)  (4).

Fig 1: The principle of mass photometry. The light scattered by a molecule attached to the measurement interface interferes with light reflected at that interface. The interference contrast scales linearly with mass.

The light scattered by a particle scales linearly with particle volume and refractive index. As the optical properties and density of proteins vary only by a few percent, their scattering signal is directly proportional to their sequence mass – making it possible to weigh single molecules with light, with high accuracy and over a large mass range (Fig 2). The correlation of scattering signal with mass holds true for a variety of biomolecules (glycoproteins, nucleic acids or lipids), making mass photometry a universal analysis tool for biomolecules in solution.

Fig 2: Mass photometry measures the molecular mass of proteins and protein assemblies in solution. Via calibration, mass photometry enables the mass measurement of unknowns with high accuracy (2% average).

(1) Verschueren, J. Cell Sci. 1985, 75, 279-301

(2) Ortega-Arroyo et al., Phys. Chem. Chem. Phys. 2012, 14, 15625-36

(3) Cole et al., ACS Photonics 2017, 4, 211-216

(4) Young et al., Science 2018, 360 (6387), 423-7

Benefits of mass photometry

Accurate measurement of true native behaviour

  • In solution, in a variety of buffers and compatible with membrane proteins

  • Label-free, without the need to modify samples
     

Information on all sub-populations in samples 

  • Single molecule counting 

  • Wide mass range and high dynamic range 

One assay format delivering multiple results

  • Homogeneity, structural integrity and activity

  • Quick, simple, minimal sample amounts