In Situ Engineeringof S-Scheme Bi2O3/Zn3In2S6 Heterojunctionson Paper-Based Architectures for Dual-Mode Photoelectrochemical–ElectrochemicalDetection of Carcinoembryonic Antigen

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.