Molecular Beacon DNA Probes with Fluorescein Bifluorophore.

An azido-derivative of a fluorescein bifluorophore was obtained and used for the synthesis of “molecular beacon”-type oligonucleotide fluorogenic probes for RT-PCR. Eight probe variants were synthesized based on an optimized sequence: with one or two quencher residues at the 3'-end, with a single or bifluorophore fluorescein label attached to 5'-end using modifying phosphoramidites (short linker) or “click reaction” (long linker). Comparison of probes in RT-PCR showed that probes with a doubled quencher (single fluorescein on a short linker) and doubled dye on a short linker (single dye) are somewhat superior in sensitivity to a standard probe (single quencher, single dye on a short linker) by the value of ΔCt = 1–2.