A signal-on electrochemical biosensor for evaluation of caspase-3 activity and cell apoptosis by the generation of molecular electrocatalysts on graphene electrode surface for water oxidation

Caspase-3 is believed to be important for diagnosis and prognosis of apoptosis-relative diseases, serving as a reliable molecular biomarker and therapeutic target. In this work, we reported a simple and sensitive electrochemical method for evaluation of cell apoptosis by determining the activity of caspase-3. Specifically, a peptide substrate specific to caspase-3 was attached on the graphene electrode surface through the hydrophobic and π-stacking interactions. Cleavage of the peptide substrate by caspase-3 resulted in the exposure of an amino terminal Cu(II) and Ni(II)-binding (ATCUN) motif on the electrode surface. The ATCUN peptide fragment can interact with Cu(II) to produce an ATCUN-Cu(II) complex which exhibits good electrocatalytic property toward water oxidation. The catalytic current increased linearly with caspase-3 concentration ranging from 0.5 pg/mL to 2 ng/mL. The method showed a detection limit of 0.2 pg/mL for caspase-3 detection. Finally, the sensor electrode was used to evaluate cell apoptosis induced by four drugs (staurosporine, vitamin C, doxorubicin and cisplatin). This work should be valuable for diagnosis and prognosis of apoptosis-relative diseases and designing of novel protease biosensors.