An enhanced silver nanocluster system for cytochrome c detection and natural drug screening targeted for cytochrome c

A label-free and turn-off fluorescence method for detecting cytochrome c (Cyt c) was developed using enhanced DNA-templated silver nanoclusters ([email protected] 80) as a novel fluorescence-enhancing nanoprobe. Cyt c-induced electron transfer between Cyt c and DNA-AgNCs results in a significant fluorescence quenching effect of DNA-AgNCs. The coated tween 80 around DNA-AgNCs particles significantly causes fluorescence signal enhancement in the solution. Meanwhile, the efficiency of fluorescence quenching by Cyt c increases substantially by adding 0.1% tween 80 (final volume concentration) into the detection system. Based on these findings, a simple method with the detection limit of 0.8 nM was established for Cyt c based on tween 80 enhanced DNA-AgNCs. A good linear relationship between the fluorescent intensity and the concentration of Cyt c ranging from 0.8 nM to 20,000 nM (R2 = 0.9910) was obtained. Consequently, the method was applied to monitor the Cyt c variation in HCT-116 and BGC-823 tumor cell culture medium after being treated with doxorubicin (DOX)and two kinds of natural compounds (J5 and S6, extracted from plants Abacopteris Penangiana and Swertia punicea Hemsl, respectively). The results indicate that the level of Cyt c in cell culture medium decreases according to the presence of DOX, J5 and S6. The reliability of the result was further confirmed by using cell viability assay and flow cytometry for apoptosis analysis (FACS). From these data, it can be concluded that this groundbreaking nanoprobe with high sensitivity, great simplicity and good biocompatibility boosts a promising outlook for exploring the molecular mechanisms of apoptosis regulation and nature drugs screening.