A ratiometric fluorescence nanosensor based on CdTe QDs for APE1 detection in breast cancer cell lysates

Apurinic/apyrimidinic endonuclease 1 (APE1) is a critical DNA repair enzyme and an emerging biomarker for cancer diagnosis. Herein, we developed a ratiometric fluorescence nanosensor using dual-emission CdTe quantum dots (R-QDs) for sensitive detection of APE1, a DNA repair enzyme and cancer biomarker. The R-QDs consist of two CdTe QDs (530 nm and 620 nm) mixed at a 1 : 3 ratio, initially showing red fluorescence. A hairpin probe (HP1) containing an AP site was labeled with biotin for magnetic bead binding and a thiol for AgNP attachment. When APE1 cleaves the probe, the AgNP fragment is released, magnetically separated, and acid-treated to release Ag⁺ ions. These ions quench the R-QDs, causing a ratiometric fluorescence change. The sensor responds linearly to APE1 from 0-0.2 U mL^-1, with a detection limit of 0.0141 U mL^-1, and shows high selectivity against other enzymes. It successfully detected APE1 in breast cancer cell lysates (MCF-7, MDA-MB-231, A549), with good linearity (R² = 0.99) and recovery rates of 94.5-107.2% (RSD < 5.2%). This method offers a reliable platform for APE1 detection in complex biological samples, aiding cancer diagnosis and treatment monitoring.