  There is a huge abundance of viruses and membrane vesicles in seawater. We
describe a new full-field, incoherently illuminated, shot-noise limited,
common-path interferometric detection method that we couple with the analysis
of Brownian motion to detect, quantify, and differentiate biotic nanoparticles.
We validated the method with calibrated nanoparticles and homogeneous DNA or
RNA.viruses. The smallest virus size that we characterized with a suitable
signal-to-noise ratio was around 30 nm in diameter. Analysis of Brownian
motions revealed anisotropic trajectories for myoviruses.We further applied the
method for vesicles detection and for analysis of coastal and oligotrophic
samples from Tara Oceans circumnavigation.
