Mechanism of direct immunofluorescence test, computer illustration. Immunofluorescence is a cell imaging technique based on the use of antibodies to label a specific target antigen (bacteria, cancer cells, other) with a fluorescent dye (also called fluorophore or fluorochrome). The fluorescent dye allows visualization of the antigen distribution in the sample under a fluorescent microscope. Direct immunofluorescence test uses a single antibody directed against the antigen that is the target of interest. This antibody is directly conjugated to a fluorescent dye.