Fluorescent nucleoside analogues (FNAs) are used as tools for the study of the structure, function and dynamics of nucleic acids and their interactions with other biomolecules. In spite of the sensitivity and the minimal perturbation to the nucleic acid environment, they are limited by their lower brightness and absorption and emission wavelengths. In order to increase the brightness, we designed a new nucleoside analogue, 8-(diethylamino)benzo[b][1,8]naphthyridin-2(1H)-one (ABN), with a push–pull conjugated system extended through a tricyclic ring resembling some of the brightest fluorophores used in photophysical studies, while maintaining a Watson–Crick hydrogen bonding motif. ABN shows a high quantum yield of 39% and a high extinction coefficient of 20,000 M<sup>-1</sup> cm<sup>-1</sup> in PBS buffer, making it one of the brightest FNAs known. When incorporated into duplex DNA, ABN shows higher quantum yields (50–53%) when base paired with adenosine, making ABN the brightest and most red shifted FNA studied in DNA. Due to its high brightness and stability, the ABN nucleoside is the first FNA to be detected in single-molecule fluorescence upon both one-photon and two-photon excitation.

ABN: New fluorescent nucleoside analogue with single-molecule detection capability.

ACS Spring Meeting 2021

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