What kind of microscope is used in FISH?
FISH signals are inherently fluorescent, generated by fluorophores such as FITC, TRITC, Texas Red, Cy3, and Cy5 attached to probes or detected via fluorescent antibody sandwiches. These faint nuclear signals require excitation with specific wavelengths and emission filter sets, which only fluorescence microscopy provides. Confocal microscopy further improves signal-to-noise ratio and optical sectioning, crucial for interphase nuclei and three-dimensional tissue FISH. Bright-field, electron, and phase-contrast microscopes cannot excite or separate fluorochrome emission, thus lacking capability to resolve locus-specific fluorescent spots against dark background.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.