Polarity-Switchable Dual-Mode Photoelectrochemical Cancer Marker Immunoassay Based on a Metal–Organic Framework@Nitrogen-Doped Graphdiyne Heterojunction

A photocurrent polarity-switching photoelectrochemical (PEC) assay has been used for its anti-interference ability and superior accuracy compared to a conventional PEC measuring system. In this work, an ultrasensitive photocurrent polarity-switchable assay was established for sensitive prostate-specific antigen (PSA) detection based on a novel metal-organic framework (MOF) and graphdiyne@polyaniline (GDY@PANI)-sensitized structure as a photoactive material. The nitrogen-doped carbon nanolayers wrapped around graphdiyne and a zinc-based MOF were synthesized via a hydrothermal method. As an excellent photoactive material, the type II heterostructure (MOF/GDY@PANI) not only reduced the recombination of generated electron-hole pairs but also resulted in a significant increase in photoelectric conversion efficiency. Furthermore, its photocurrent was 4.6-fold higher than that of GDY@PANI and 37-fold higher than the proposed MOF. The integrated MOF/GDY@PANI/antibody (Ab) glassy carbon photoelectrode (GCE) was used as a PEC immunosensor for PSA detection (signal-off mode) and exhibited a wide linear dynamic range from 0.1 fg/mL to 10 pg/mL and a limit of detection of 0.05 fg/mL. The GCE modified with MOF and primary antibody (Ab1) (GCE/MOF/Ab1) produced a cathodic photocurrent, and in the presence of PSA, after the introduction of GDY@PANI-labeled-secondary antibody (Ab2) onto the surface of GCE/MOF/Ab1 and formation of an immunocomplex, the photocurrent amplified and switched to an anodic current. Due to high photoelectric conversion efficiency and good polarity-switching ability of GDY@PANI, the proposed immunosensor presented a turn-on photoelectrochemical performance for PSA detection at a wide linear range from 0.1 to 10 pg/mL and ultralow detection limit of 0.03 fg/mL. Compared to signal-off mode, the sensitivity increased 2-fold and the effect of interferences produces more reliable results due to photocurrent switching, and its effectiveness was evaluated against an enzyme-linked immunosorbent assay (ELISA) using spiked real human serum samples. The positive and promising outcomes achieved by the proposed immunosensor imply that the developed platform has the potential to serve as an excellent enzyme-free photoanode immunosensor for early cancer diagnosis and therapeutic monitoring.