It is essentially an interferometric approach that allows to measure mass (i.e. the total scattered intensity) of proteins. It is commercialized by Refeyn, and I wonder how similar it is to the ExoView devices (are they somehow related to each other?) This is the same technique used by Illumion, and is similar to what Envue is developing for nanoparticle tracking analysis.
iNTA is a similar implementation but without the need for particle to attach to the substrate.
These are the other notes that link to this one.