A schematic of two dark-field microscopy configurations. Left: A dark-field condenser illuminates the substrate at angles higher than the collection numerical aperture. Only scattered light is collected, resulting in images with a dark background. Right: Excitation light from a dark-field immersion epi-objective is totally internally reflected at the coverglass-sample interface. While a dark-field condenser allows detection of nanoparticles anywhere within a thick transparent sample, TIRM tends to have better stray light rejection but is limited to detecting particles within about 200 nm of the coverglass-sample interface. (Left: Adapted from . Right: Adapted from ).