Freestanding plasmonic BiVO4@AuNPs//dendritic CdS QDs with programmable carrier-direction switching for low-background photoelectrochemical PARP-1 detection in cancer tissues.

Precise manipulation of interfacial charge carrier transport is essential for developing high-performance photoelectrochemical (PEC) biosensors with minimal background and high anti-interference capability in complex matrices. In this work, we present a novel low-background PEC biosensing platform capable of programmable switching of carrier transfer direction for the sensitive detection of PARP-1 in cancer tissues. The sensing architecture is based on freestanding plasmonic Schottky junctions formed by integrating Au nanoparticles into electrospun BiVO4 nanofibers. These junctions not only invert the inherent carrier transport direction but also suppress the background photocurrent to nearly zero through localized surface plasmon resonance effects. Upon target recognition, PARP-1 binds to thiol-modified double-stranded DNA (SH-dsDNA) and catalyzes the transfer of biotinylated ADP-ribose from NAD+, yielding SH-dsDNA-PARP-1 copolymers. Subsequent introduction of streptavidin-conjugated single-stranded DNA triggers hyperbranched rolling circle amplification, generating elongated DNA templates that selectively capture complementary DNA-functionalized CdS quantum dots (QDs). Capitalizing on the intrinsic sulfhydryl groups of the copolymer, high-density CdS QDs are assembled via multivalent Au-S bonds, forming a dual-template structure comprising the PARP-polymer conjugate and a dendritic DNA scaffold. This design enables programmable QD organization, facilitating one-to-many cascaded signal amplification and programmable switching of carrier transfer direction. By combining the near-zero background of BiVO4@AuNPs with the dramatically enhanced cathodic photocurrent from the densely grafted CdS QDs, the constructed "On-Off-super On" biosensor achieves an exceptional detection limit of 4.48 × 10-7 U·μL-1 for PARP-1 over a broad linear range in lung cancer tissue. This study offers a universal strategy to be used for clinical diagnosis and PARP-1 inhibitor research.