A new label technology for the detection of specific polymerase chain reaction products in a closed tube.

A novel signal generation principle suitable for real time and end-point detection of specific PCR products in a closed tube is described. Linear DNA probes were labeled at their 5'-ends with a stable, fluorescent terbium chelate. The fluorescence intensity of this chelate is lower when it is coupled to single-stranded DNA than when the chelate is free in solution. The synthesized probes were used in the real time monitoring of PCR using a prototype instrument that consisted of a fluorometer coupled to a thermal cycler. When the probe anneals to a complementary target amplicon, the 5'-->3' exonucleolytic activity of DNA polymerase detaches the label from the probe. This results in an enhanced terbium fluorescence signal. Since terbium has a long excited state lifetime, its fluorescence can be measured in a time-resolved manner, which results in a low background fluorescence and a 1000-fold signal amplification. The detection method is quantitative over an extremely wide linear range (at least 10-10(7)initial template molecules). The label strategy can easily be combined with existing label technologies, such as TaqMan 5'-exonuclease assays, in order to carry out multiplex assays that do not suffer from overlapping emission peaks of the fluorophores.