Fluorescence Microscopy

Basic Setup
Intense light source such as a mercury vapor lamp.

Exciter filter which blocks out wavelengths longer than 400nm, which means only ultraviolet light is let through.

Fluorescent dye such as Auramine O, which absorbs the UV light to re-emit the light at a longer wavelength that will pass through the barrier filter.

Barrier filter which filters out wavelengths less than 500nm in order to protect eyes from UV radiation

Appearance
The field is black if no specimen is present because of the filters. The object will shine, similarly to the image of a dark field microscope but with colors.

Uses
Used for bacteria that have a high lipid content and that are therefore hard to stain with conventional stains. Some organisms commonly observed using fluorescence microscopy are mycobacterium, especially mycobacterium tuberculosis, because the Auramine O dye will only stain waxy bacteria, which normally do not live in the human body.

Acid Fast Technique
Acid fast staining can be used to observe waxy bacteria under a light microscope. It is a special method of staining that should be used with the oil immersion lens. It is difficult to focus and can therefore take a long time to complete the observation.

Immunofluorescence
Attatches the fluorescent dye to an antibody that is then exposed to a sample. If the antibody reacts with the sample, it will be observable under the microscope. This allows one to see organisms that do not have a waxy content, such as Streptococcus pyogenes and Treponema pallidum.