Gold nanocluster-based fluorescence turn-off probe for sensing of doxorubicin by photoinduced electron transfer

Doxorubicin (DOX), an anthraquinone-based anticancer drug, is effective for the treatment of a variety of human tumors. However, due to its narrow therapeutic window, serum levels need to be closely monitored. Herein, we report the development of a novel fluorescence probe based on gold nanoclusters co-modified with dithiothreitol (DTT) and carboxylated chitosan (CC) (CC/DTT-AuNCs) for the determination of DOX. The emission from the CC/DTT-AuNCs is significantly suppressed by DOX. The fluorescence-quenching mechanism involving DOX was systematically explored, and photoinduced electron transfer was identified to play a dominant role. DOX readily binds to the CC/DTT-AuNC surface through electrostatic attraction, after which it accepts the electron from the photoexcited CC/DTT-AuNC and quenches its fluorescence. We found that other anthraquinone structures (e.g., alizarin and emodin) devoid of –NH 2 groups exhibited almost no CC/DTT-AuNCs fluorescence-quenching effect due to weak electrostatic interactions between these anthraquinones and the NCs. A linear relationship between photoluminescence suppression and the concentration of DOX was observed in the 0.05–2 μM range under the optimal experimental conditions, with a detection limit as low as 5 nM. This new sensing approach was also used to successfully measure DOX in human serum samples with satisfactory results obtained.