Reliable FRET-ON imaging of telomerase in living cells by a tetrahedral DNA nanoprobe integrated with structure-switchable molecular beacon.

• A FRET-ON nanoprobe for cellular telomerase probing was developed based on a functionalized tetrahedral DNA structure. • The mechanism and reliable imaging of the proposed nanoprobe were systematically validated. • The telomerase primer integrated with the molecular beacon enhanced the telomerase recognition with high sensitivity. • The ratiometric nanoprobe could indicate telomerase activity changes and differentiate tumor cells from normal cells. Precise in situ monitoring of telomerase is highly informative in early cancer diagnosis. However, the complicated biological environment makes it difficult for conventional fluorescent probes to achieve effective cell penetration, stable delivery and accurate intracellular imaging. In this study, we design a functionalized tetrahedral DNA nanoprobe (TDNp) with fluorescence resonance energy transfer (FRET) feature to image telomerase in living cells. The proposed TDNp is composed of a DNA tetrahedral structure to improve stability and cellular permeability, a telomerase primer and a FRET-based molecular beacon (MB) to report fluorescent signal. In the presence of telomerase, the primer is extended and a free MB is recovered to trigger FRET response. The " off-on " FRET signal benefits accurate telomerase sensing with low false-positive feedback. By orienting the primer at the vertices of TDNp, we can sensitively detect telomerase with a detection limit of 35 HeLa cells. Furthermore, the TDNp could effectively distinguish cancer cells from normal cells, and is successfully applied to monitor the changes of telomerase activity in living cells. As a summary, the TDNp provides stable and reliable imaging of intracellular telomerase for cancer diagnosis. [ABSTRACT FROM AUTHOR]