Labeling of oligonucleotides with fluorescein

The labeling of oligonucleotide probes using a fluorescein-labeled nucleotide is described. The reaction is characterized by careful control of the nucleotide and probe molar ratio in order to produce a tail that gives good detection sensitivity without compromising hybridization stringency control of the probe sequence. The labeling reaction can be easily monitored for incorporation of the fluorescent label and the probes can be used in many applications.