Integration of MOF-derived ZnO/BiS/ZnInS double Z-scheme heterostructure and dual-enzyme active HPAu/Ag@AFGQDs nanospheres for PEC/colorimetric dual-mode bioassay of caspase-3 activity.

Caspase-3 is an important biomarker of apoptosis-relevant diseases, so it has great clinical value to determine caspase-3 activity. Herein, an innovative photoelectrochemical (PEC)/colorimetric dual-mode biosensor was established for highly sensitive and reliable determination of caspase-3 activity. The advanced Zn-based metal organic framework (Zn-MOF)-derived ZnO polyhedrons/BiS nanorods/3D sakura-like ZnInS double Z-scheme heterostructure was prepared by layer-by-layer assembly on the indium tin oxide electrode (termed as ZnInS/BiS/ZnO/ITO), which offered a strong initial photocurrent. The hollow porous gold/silver nanospheres@amino functionalized graphene quantum dots (HPAu/Ag@AFGQDs) with nanozyme activity were designed as dual-signal converters. In a homogeneous system, the caspase-3-specific peptide was connected on the FeO@Au nanoparticles, and further modified with HPAu/Ag@AFGQDs nanospheres. After caspase-3-specific recognition and shear for peptide, some HPAu/Ag@AFGQDs nanospheres were detached from FeO@Au nanoparticles. The freed HPAu/Ag@AFGQDs nanospheres were introduced on the ZnInS/BiS/ZnO/ITO electrode to trigger multiple quenching signal effects (peroxidase mimetic enzymatic catalytic sediment effect; competing effect of the generated sediment for photoexcited electrons; steric hindrance effect). Simultaneously, the freed HPAu/Ag@AFGQDs nanospheres acted as oxidase mimetics to catalyze 3, 3', 5, 5'-tetramethylbenzidine (TMB) oxidation. Resultly, the photocurrent response decreased while absorption intensity enhanced, thus achieving the reliable and accurate PEC/colorimetric dual-mode detection for caspase-3 activity, which highlighted the potential practicability of the dual-mode biosensor for real cell sample assay.