The Heptan (in-direct) method of labeling in fluorescence in-situ hybridization (FISH) is a technique used to tag nucleic acid probes with a fluorescent signal that can be visualized under a fluorescence microscope. The term "indirect" in this context refers to the fact that the fluorescent tag is not directly attached to the probe but is instead introduced in a multi-step process, often involving a hapten molecule

Detecting heptane indirectly after chemical derivatization (coding) typically involves converting heptane into a more detectable form, such as a product that is more reactive or has a distinct spectral signature.