In Situ Engineering of S-Scheme Bi2O3/Zn3In2S6 Heterojunctions on Paper-Based Architectures for Dual-Mode...

The integration of multimodal signaling into paper-based analytical devices (PADs) provides a robust means to enhance reliability in point-of-care diagnostics. Herein, we demonstrate a highly sensitive dual-mode immunosensing platform, integrating photoelectrochemical (PEC) and electrochemical (EC) detection via the in situ architectural engineering of an S-scheme Bi2O3/Zn3In2S6 heterojunction directly onto cellulose fiber scaffolds. The spatial decoupling and synergistic charge migration inherent to the S-scheme interface significantly amplify the initial photocurrent response, providing a high-performance foundation for sensing. A sandwich-type bioconjugate assembly was implemented, utilizing SiO2/AuNPs nanoparticle-labeled secondary antibodies (SiO2/AuNPs-Ab2) as multifunctional signal modulators. The PEC signal experienced a dramatic, concentration-dependent attenuation owing to the synergistic interplay between the steric hindrance provided by SiO2 and the SPR effect provided by AuNPs. With a wide linear range of 0.001 to 100 ng mL-1, the platform exhibited excellent detection limits of 0.077 pg mL-1 (PEC) and 0.12 pg mL-1 (EC) for carcinoembryonic antigen (CEA) under optimized conditions. The dual-signal output enables intrinsic mutual validation, significantly mitigating false-positive risks. Given its modular design and exceptional sensitivity, this PADs-based heterojunction platform represents a versatile architecture for the early diagnosis of diverse clinical biomarkers.