Self-powered PEC platform with large and stable photocurrent for blocker-free sensitive assay of Caspase-3 activity based on CdIn2S4/CdS QDs anode and NH2-MIL-125(Ti)@MAPbI3/Au NPs cathode.

The diagnosis of apoptosis is of particular importance for assessing apoptosis-related disease progression and improving the therapy efficiency. Caspase-3 is the most frequently activated cysteine protease and a key mediator of cell apoptosis, therefore, its activity assay is vital. Here, by encapsulating of MAPbI3 in NH2-MIL-125(Ti) and constructing "Z-scheme" structure between CdIn2S4 microspheres and CdS quantum dots (QDs) to obtain high-photoelectrochemical (PEC)-stability and large-photocurrent NH2-MIL-125(Ti)@MAPbI3/Au NPs photocathode and CdIn2S4/CdS QDs photoanode, respectively, a new dual-photoelectrode self-powered PEC platform was constructed for highly sensitive and blocker-free assay of caspase-3 activity. The designed negatively-charged CC-DEVD-peptide chains were immobilized on the positive-charged NH2-MIL-125(Ti)@MAPbI3/Au NPs hybrids in flat-lying state due to the electrostatic interaction and double Au-S bonds to maximally suppress the photocurrent signal and to make blockers be not needed. When caspase-3 was present, the CC-DEVD-peptide chains were specifically recognized and cleaved, and only a short Cys-Cys dipeptide remained on the NH2-MIL-125(Ti)@MAPbI3/Au NPs/ITO photocathode, leading to an obviously enhanced photocurrent. Due to the good PEC properties and the matched energy levels of CdIn2S4/CdS QDs and NH2-MIL-125(Ti)@MAPbI3/Au NPs, the developed dual-photoelectrode self-powered PEC platform had large open circuit voltage and photocurrent, and the caspase-3 activity was sensitively assayed (linear range, 0.1 pg mL-1 - 1.0 μg mL-1; detection limit, 5.7 fg mL-1), implying its promising applications in assessment of disease progression and therapy efficiency associated with apoptosis, and rapid screening of caspase-3-related drugs.