  Optical sensing is one of the key-enablers of modern diagnostics. Especially
label-free imaging modalities hold great promise as they eliminate labeling
procedures prior to analysis. However, scattering signals of nanometric
particles scale with their volume-square. This unfavorable scaling makes it
extremely difficult to quantitatively characterize intrinsically heterogeneous
clinical samples, such as extracellular vesicles, as their signal variation
easily exceeds the dynamic range of currently available cameras. Here, we
introduce off-axis k-space holography that circumvents this limitation. By
imaging the back-focal-plane of our microscope we project the scattering signal
of all particles onto all camera pixels thus dramatically boosting the
achievable dynamic range to up-to 110 dB. We validate our platform by
detecting, and quantitatively sizing, metallic and dielectric particles over a
200x200 $\mu$m field-of-view and demonstrate that independently performed
signal calibrations allow correctly sizing particles made from different
materials. Finally, we present quantitative size-distributions of extracellular
vesicle samples.
