Visual monitoring of cisplatin-regulated caspase-3 activity in living cells based on a reduced graphene oxide-loaded fluorescent probe.

Cisplatin (DDP) is a potent chemotherapeutic drug, which can regulate tumor cell apoptosis by up-regulating caspase-3 activity. Thus, monitoring caspase-3 activity in breast cancer cells can directly illustrate the efficiency of DDP treatment. In this study, by using reduced graphene oxide (rGO) as a quencher of a fluorescence labeled peptide, we developed an "off to on" method to monitor the effect of DDP on caspase-3 in breast cancer cells. In this method, the rGO quenched fluorescence with an ultra-high level of efficiency. Caspase-3 hydrolyzed the polypeptide probe, generating two segments of different lengths. The release of a short segment marked with fluorophores led to the recovery of the fluorescence signal (Ex/Em = 450/521 nm). Under the optimal conditions, the linear range of caspase-3 was 0.4-7 U mL -1 and the limit of detection was 0.33 U mL -1 . The upregulating effect of DDP on intracellular caspase-3 activity was visualized with the "off to on" method and flow cytometry assay showed that caspase-3 activity increased along with the apoptosis rate of tumor cells. The above results show the practical application of the method for evaluating the efficacy of drugs against cancer cells.