Lanthanide ions as fluorescent probes for the nucleotides

The lanthanide ions reacted with the nucleotides to form a complex in which the lanthanides served as sensitive fluorescent probes. By selectively exciting the nucleotide, the quantum efficiency of narrow-line lanthanide ion fluorescence can be calculated. Quantum efficiency values of 0.19 to 0.01 and 0.14 to 0.01 were obtained for Tb⁺³ and Eu⁺³ respectively. For Dy⁺³ and Sm⁺³ the values were too low to measure accurately for most nucleotides. The binding of the lanthanides to the nucleotides can be reversed by prolonged dialysis against chelating agents. Between pH 3 and pH 7 the complex precipitates and approaches a maximum of lanthanide ion fluorescence at pH 5.5.