In this work, the authors use interferometric light scattering microscopy (iSCAT) to characterize the mass of individual proteins. They also demonstrate how the technique can be applied to characterize small-molecule binding, glycoprotein cross-linking and protein assembly. The technique offers a label-free method of detection and characterization, and the current paper builds on previous work of the Kukura group by applying recent advances in resolution capabilities to this host of examples. The technique itself is far better described in this previous paper, which will also be discussed. "Label-Free Single-Molecule Imaging with Numerical-Aperture-Shaped Interferometric Scattering Microscopy." D. Cole et al., ACS Photonics 4, 211-216 (2017). If you're interested more in the technique than the biological examples, read this article instead!