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 200 × 200 μm 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.
Keywords: Fourier imaging; extracellular vesicles; holography; interferometric microscopy; label-free.