Hot-Hole Injection-Enabled Efficient Signal Modulation for Boosting Sensitive Paper-Based Photocathodic Analysis through an Atom-Shared Plasmonic Hetero-Nanostructure

Cathodic photoelectrochemical (PEC) assay with superior anti-interference capacity and high photocorrosion resistance demonstrates great advantages in real sample analysis. However, it suffers from unsatisfactory cathodic PEC response, resulting in inferior detection performance. Herein, a hot-hole injection effect (HIE)-enabled PEC signal modulation strategy with exceptional target responsiveness is first proposed based on atom-shared plasmonic Bi-Bi₂O₃ (AS-BBO) hetero-nanostructure with enriched oxygen vacancy. The coshared Bi atoms at the AS-BBO heterointerface foster an atomic-level intimate-contact interface between Bi₂O₃ and plasmonic Bi. This elaborately designed configuration effectively shortens the carrier diffusion distance and reduces the interfacial energy barrier, thereby enabling efficient injection of short-lived hot holes from plasmonic Bi into Bi₂O₃ photocathode, leading to a greatly increased charge carrier density. Meanwhile, the oxygen vacancies efficiently prolong the lifetime of the charge carriers in AS-BBO, further improving photo-to-current conversion efficiency. Consequently, the AS-BBO generated a significantly enhanced cathodic PEC signal due to the HIE facilitated by oxygen vacancies. To realize sensitive photocathodic analysis, target-level controlled HIE efficacy was designed by exploiting CoFe₂O₄ as a hole sink to harvest photoinduced holes from AS-BBO, which resulted in a sharp quenching of the robust initial photocurrent signal owing to diminished HIE. Leveraging this substantial photocurrent variation, a highly sensitive paper-based photocathodic sensing platform was developed for microRNA-221 detection, achieving a low detection limit (80 aM) and a wide linear range (0.25 fM to 2 nM). This work laid the foundation for exploiting HIE as an efficient signal modulation strategy for high-performance photocathodic analysis.