Abstract：The fluorescence of Tb3+ is not quenched after the rare earth ion is combined with DNA. The fluorescence intensity is related not only to the kinds of bases of DNA but also to the kinds of DNA. The rare earth ion Tb3+ was used as the fluorescence probe to detect the formation of triplex DNA. The results show that the fluorescence intensity of Tb3+ combined with polydA is much stronger than that of Tb3+ combined with polydT，which testifies that the fluorescence intensity is related to the kinds of bases combined with Tb3+. The results also demonstrate that the rare earth ion can be used to detect those three forms of DNA though their fluorescence peak positions are similar when Tb3+ as a fluorescence probe is combined with single strand DNA (ssDNA), double helix DNA (dsDNA)，and triple helix DNA (tsDNA)，respectively. However，their intensities are quite different. The fluorescence intensity of Tb3+ combined with ssDNA-Tb3+ is the largest. And the fluorescence intensity of Tb3+ combined with tsDNA-Tb3+ takes the second place. The minimum peak intensity belongｓ to the contribution of Tb3+ coupled with dsDNA-Tb3+. The reason is that the capability of energy transference of ssDNA, dsDNA and tsDNA is different. The different degree of energy transference influences the intensities of Tb3+. The influences of pH and the metal ion on the formation of triplex DNA were also studied. The authors found that the neutral pH and high valence metal ion are beneficial to the formation of ts-DNA.
Key words：Tb3+;DNA;Formation of triplex DNA;Fluorescence spectra;Hoogsteen hydrogen bond
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