An in-situ sampler for collecting small samples of suspended sediment for microscopic analysis bas been built and tested. The device rapidly freezes a thin layer of water entrapping all of the suspended particles in it; when the sampler is recovered, the disc of ice is placed on a suitable substrate and freeze-dried. The particles can then be examined in an undisturbed state with a light microscope or with an electron microscope.
Schubel, J. R., and E. W. Schiemer. 1972. "A device for collecting in-situ samples of suspended sediment for microscopic analysis." Journal of Marine Research 30, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1243