  Chip-based Evanescent Light Scattering (cELS) utilizes the multiple modes of
a high-index contrast optical waveguide for near-field illumination of
unlabeled samples, thereby repositioning the highest spatial frequencies of the
sample into the far-field. The multiple modes scattering off the sample with
different phase differences is engineered to have random spatial distributions
within the integration time of the camera, mitigating the coherent speckle
noise. This enables label-free superior-contrast imaging of weakly scattering
nanosized specimens such as extra-cellular vesicles (EVs) and liposomes,
dynamics of living HeLa cells etc. The article explains and validates
experimentally the physics behind cELS by demonstrating a multi-moded straight
waveguide as a partially coherent light source. For isotropic super-resolution,
spatially incoherent light engineered via multiple-arms waveguide chip and
intensity-fluctuation based algorithms are used. The proof-of-concept results
are demonstrated on 100 nm polystyrene beads and resolution improvement of
close to 2X is shown. cELS also realizes (2-10)X more contrast as opposed to
conventional imaging techniques. In addition, cELS platform is miniaturized and
enables large field-of-view imaging compared to state of the art label-free
techniques. cELS holds a potential for label-free super-resolution imaging of
nanosized biological specimens at high-throughput.
