This french company started in 2017 and sells the Video Drop, a device that uses interferometry to detect particles (similar to SP-IRIS but perhaps even more closely related to iSCAT). The setup is described in [@boccara2016Full-field interferometry for counting and differentiating aquatic biotic nanoparticles: from laboratory to Tara Oceans] and follows the schematic below:
The technique itself relies on NTA to measure the size, but they also provide accurate results from scattering, in a very similar approach to nanoparticle tracking in hollow optical fibers of Dispertech.
I still wonder how precise the measurement of scattering intensity can be, taking into account that that it is highly sensitive to the position of the particles in the focal plane and that particles are freely diffusing in 3D.
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