8248 - Mass photometer

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DTU plans to purchase a mass photometer, which is based on the principle of interferometric scattering microscopy. The purpose is to detect and quantify individual macromolecules and particles in a label-free manner, purely by their scattered light. The (molecular) mass of the individual molecules and particles can be determined, which is why the method is sometimes described as “weighing molecules with light”. Light scattering intensity from particles in solution normally scales with the sixth power of the particle radius (Raleigh scattering). However, if particles are very close to a reflective surface, the interference between scattered and reflected light decreases the size dependence of the scattered light intensity such that it scales only with the 3rd power of the particle radius (interferometric light scattering, iSCAT). This latter option has been implemented by the company Refeyn in the TwoMP instrument. The absence of any need to label the molecules to be studied, as well as the lower limit of detection (30 kDA, corresponds to an individual middle-sized protein molecule) renders this method highly suitable to study the interactions, assembly and aggregation of biological molecules. Examples include antibody binding to antigens, oligomerisation events and phase separation. This methodology will be of great use in many different projects in the Protein Biophysics group at DTU Bioengineering and in other projects in this department and beyond. The protein biophysics groups works on protein assembly and association phenomena in areas ranging from human health over biotechnology and food science and the mass photometry instrument will be used in all these areas. Mass photometry provides unique benefits compared to other solution-based biophysical methods, as it derives molecular mass not indirectly from a measurement of the hydrodynamic radius (e.g. SEC or DLS) but from light scattered by single molecules, making it uniquely suited to differentiate between particles of similar size but different mass (e.g. loaded vs. unloaded gene delivery particles). As the mass of a particle scales with the 3rd power of its radius (for constant density), the resolution in the mass dimension is also much higher than in the size dimension, allowing discrete sizes of oligomeric assemblies to be discerned. This is basically impossible in any size-based analysis. As mass photometry measures the mass of each molecule individually it is uniquely suited to in-form about complex samples and processes including sub-populations lost in ensemble measurements (e.g. SPR, BLI or DLS). The measurements can be done directly in solution, on minimal sample amounts and in a variety of buffer conditions. The Refeyn TwoMP mass photometer is currently the only commercial system available providing single-molecule scattering contrast of sufficient quality, reproducibility and stability to allow for direct correlation to molecule mass. As there are no alternative vendors DTU intends to award the contract to Refeyn GmbH.