Photoelectrochemical (PEC) immunoassays with ultrasensitive detection abilities are highly desirable for in vitro PEC diagnosis and biological detection. In this paper, dual Zscheme PEC immunoassays with hierarchical nanostructures (TiO 2 @NH 2 -MIL-125@CdS) are synthesized through epitaxial growth of MOF-on-MOF and further in situ derivatization. The dual Z-scheme configuration not only extends the light absorption range but also increases the redox ability due to the interface structure nanoengineering, which synergistically suppresses bulk carrier recombination and promotes the charge transfer efficiency at the electron level. Furthermore, a smart MOF-derived labeling probe (CuO@ZnO nanocube) is designed to develop a split-type PEC biosensor by using prostate-specific antigen (PSA) as a target biomarker. In the presence of PSA, the Ab 2 -labeled CuO@ZnO would specifically bond to the dual Z-scheme electrode. Then, the MOF-derived CuO@ZnO is dissolved by hydrochloric acid to release Cu 2+ , which could replace Cd 2+ via an ion-exchange reaction, thus leading to the decrease of the photocurrent due to the destruction of the dual Z-scheme configuration. In typical applications, the split-type PEC immunoassay exhibits an excellent detection performance for PSA with a LOD as low as 0.025 pg•mL −1 .

Designing semiconductor-based heterojunctions for achieving high-efficiency electron–hole separation and rapid catalytic kinetics is highly important for promoting photoelectrochemical water oxidation performance. Herein, we synthesize a dual-cocatalyst-decorated heterostructure (TiO2/CdS/CoSx/NiS) via in situ metal–organic framework (MOF) derivation. The homogeneous dispersion of CoSx/NiS, benefiting from the MOF derivation of atomic metal building blocks, significantly accelerates the catalytic kinetics and decreases the overpotential of the water oxidation process. Meanwhile, the CoNi MOF-derived TiO2/CdS heterojunctions simultaneously improve the electron–hole separation and extend the absorption range due to the formation of an oriented electromagnetic field and narrow bandgap of CdS. The as-prepared TiO2/CdS/CoSx/NiS exhibits excellent performance toward photoelectrochemical water oxidation with a photocurrent density of up to 5.10 mA/cm2. The practical production rate of O2 is about 22.25 μmol·h–1·cm–2, which is higher than those of TiO2/CoNi-MOF (18.69 μmol·h–1·cm–2) and bare TiO2 (13.80 μmol·h–1·cm–2). This study offers a promising solution to tailor the growth and dispersion of high-quality dual-cocatalysts and paves the way toward the commercial realization of water-splitting systems.

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