Dark-field microscopy

Optical dark fields usually done with an condenser that features a central light-stop in front of the light source to prevent direct illumination of the focal plane, and at higher numerical apertures may require oil or water between the condenser and the specimen slide to provide an optimal refractive index.

Dark-field microscopy is a very simple yet effective technique and well suited for uses involving live and unstained biological samples, such as a smear from a tissue culture or individual, water-borne, single-celled organisms.

When coupled to hyperspectral imaging, dark-field microscopy becomes a powerful tool for the characterization of nanomaterials embedded in cells.

In a recent publication, Patskovsky et al. used this technique to study the attachment of gold nanoparticles (AuNPs) targeting CD44+ cancer cells.

In polycrystalline specimens, on the other hand, dark-field images serve to light up only that subset of crystals that are Bragg-reflecting at a given orientation.

As with analog dark-field imaging in a transmission electron microscope, it allows one to "light up" those objects in the field of view where periodicities of interest reside.

Unlike analog dark-field imaging it may also allow one to map the Fourier-phase of periodicities, and hence phase gradients, which provide quantitative information on vector lattice strain.

Red blood cells as seen by darkfield microscopy x 1000
A cross-section of a nematode , photographed with an oil dark field condenser with a numerical aperture of 1.40
Diagram illustrating the light path through a dark-field microscope
Dark-field microscopy produces an image with a dark background
Operating principles of dark-field and phase-contrast microscopies
Weak-beam DF of strain around nuclear track cores
Digital dark-field simulation of 2 nm metal particles on a nano-cylinder
Digital dark-field image of internal twins