3′-End Labeling of Oligonucleotides with Fluorescein-11-dUTP and Enhanced Chemiluminescent Detection

In this reaction, the enzyme terminal transferase is used to introduce a short tail of fluorescein nucleotides to the 3′-end of an oligonucleotide (1 ) followed by horseradish peroxidase-catalyzed enhanced chemiluminescent detection of the labeled hybrids. This approach is used in the ECL 3′-oligolabeling and detection system (Amersham International, Amersham, UK) for hybridizations on membranes. In general, oligonucleotide probes are used for lower sensitivity applications, and the combination of fluorescein-labeling and enhanced chemiluminescent detection allows as little as 20 � 10⁻¹⁸ mol of homologous target to be detected within a 1-h exposure.