An "off-on" CdTe QDs fluorescent nanosensor for detecting apoptosis in osteosarcoma and evaluating chemotherapy response.

This work presents a novel “off-on” fluorescent nanosensor for detecting apoptosis and evaluating chemotherapy efficacy in osteosarcoma. The sensor is constructed by conjugating carboxyl-modified CdTe quantum dots (CdTe QDs) to a BHQ1-labeled peptide substrate containing the caspase-3-specific DEVD sequence. Caspase-3 activation, a hallmark of apoptosis, cleaves the peptide, releasing the BHQ1 quencher and restoring QD fluorescence. The sensor demonstrated high sensitivity and selectivity for caspase-3, excellent stability, and minimal cytotoxicity. Applied to cell lysates, the sensor effectively detected chemotherapy-induced apoptosis in osteosarcoma cells, showing a dose-dependent fluorescence response to cisplatin and doxorubicin treatment that correlated with drug efficacy. Notably, the sensor revealed significantly higher baseline caspase-3 activity in osteosarcoma cells compared to normal osteoblasts, and enabled quantitative monitoring of apoptotic response upon drug treatment. This platform offers a promising tool for osteosarcoma theranostics.