A turn-on fluorescent biosensor based on CdTe quantum dots for sensitive and selective detection of APE1 activity in...

Apurinic/apyrimidinic endonuclease 1 (APE1) plays a critical role in the base excision repair (BER) pathway, and its aberrant activity is closely associated with various cancers, including cervical cancer, as well as neurodegenerative diseases. Herein, we report a novel "turn-on" fluorescent biosensor for the sensitive and selective detection of APE1 activity based on CdTe quantum dots (QDs) and silver ions (Ag⁺). The sensing strategy relies on the inner filter effect (IFE)-induced fluorescence quenching of CdTe QDs by Ag⁺, followed by fluorescence recovery upon specific cleavage of an AP site-containing dsDNA probe by APE1. The released poly-C fragments competitively bind with Ag⁺, separating Ag⁺ from the surface of CdTe QDs and restoring the fluorescence. Under optimized conditions, the biosensor exhibits a linear response to APE1 activity in the range of 2-10 U mL^-1 with a detection limit as low as 0.09 U mL^-1. The sensor demonstrates excellent selectivity against interfering biomolecules, good stability, and reproducibility. Moreover, it was successfully applied to detect APE1 activity in HeLa cell lysates, showing satisfactory recovery rates. This work provides a green, simple, and robust platform for APE1 activity detection in complex biological matrices, with potential applications in cancer-related biomedical research.