Fluorescent label, definition

In some physical chemistry texts, the primary photochemical process is incorrectly considered to be no more than the absorption of radiation. Such a definition is not acceptable because absorption is not a chemical transformation and, more important, because it does not correspond to current usage in photochemistry. These texts then label such diverse processes as fluorescence, dissociation of an excited molecule, and chain reactions, all as different types of secondary photochemical processes. This is also unacceptable because "secondary" has come to have a specific meaning (as is discussed in Section III.A.3) which does not apply to all of these transformations, and also because some of them are not chemical. Photochemists instead use primary and secondary in the original sense of Bodenstein. 

Different biological questions can be addressed using different ON probe structures conveniently labeled with a selected F that exploits the main characteristics of fluorescence, which is the most sensitive spectroscopic technique (10). Their definitions are widely reported in companion articles and will not be discussed here. The applications can be divided into different series. One application concerns synthetic FONs that mimic the different structures found in living systems and aims at structural, dynamics, and interaction studies in vitro. Another... 

Slide 2 (Fig.2) shows a lymphocyte containing a fluorescent F-body, i.e. a Y chromosome, and the same cell after autoradiography. This definitely proves that the HG-PRT deficient lymphocytes have somehow received and incorporated the label. 

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