A novel bifunctional europium complex as a potential fluorescent label for DNA detection

Abstract

A bifunctional europium complex of Eu(TTA)₃(5-NH₂-phen) using 2-thenoyltrifluoroacetonate (TTA) and 5-amino-1,10-phenanthroline (5-NH₂-phen) as ligand reagents was applied in DNA detection assays for the first time. The complex has a long fluorescence lifetime, high fluorescence quantum yield, and is easy to label oligonucleotides for time-resolved fluorescence bioanalysis. A two-probe tandem DNA hybridization assay including capture DNA₁, probe DNA₂, and target DNA₃ was employed to detect microbial pathogens. The DNA sequences in the assay were designed using software Primer Premier 5.0 based on published specific nucleotide sequences of Staphylococcus aureus and Escherichia coli. 3′-Amino-modified capture DNA₁ was covalently immobilized on the common glass slide surface and the 5′-amino-modified probe DNA₂ was combined with the functionalized Eu(TTA)₃(5-NH₂-phen) via glutaraldehyde. The detection was done by monitoring the fluorescence intensity from the glass surface after the hybridization reaction with complementary target DNA₃. The optimal concentration of capture DNA₁ of 1.0 × 10⁻⁶ mol l⁻¹ dropped onto the glass slides and optimal hybridization temperatures of 48 °C and 39 °C respectively for Staphylococcus aureus and Escherichia coli were obtained. The proposed DNA detection system showed higher sensitivity than such a complex doped nanoparticle-based detection system in our previous study for the better uniformity and dispersity of monomolecular labels. The sensing system presented a short hybridization time of 2 h, satisfactory stability, and high selectivity. The results demonstrate that this complex might be a potentially excellent dye in area of biochemical analysis.