Development of Hierarchical Tandem Heterojunction with Visible Light Enhanced Peroxidase-Like Activity for All-in-Capillary Self-Calibrating SERS Immunoassay of Aβ₁₋₄₂.

Aiming to meet the critical need for user-friendly and sensitive clinical analysis platforms, an all-in-capillary SERS analytical system integrated with a visible-light-enhanced nanozyme for highly sensitive and convenient biomarker detection was developed. The system employs a hierarchical tandem heterojunction (TiO₂/MoS₂/CoFe₂O₄) as a peroxidase-like nanozyme, which significantly enhances separation and transfer of photogenerated charges under visible light. This nanozyme catalyzes the oxidation of leucocrystal violet to crystal violet, generating a characteristic Raman signal at 923 cm⁻¹. To ensure analytical reliability, the inner wall of the capillary was modified with TiO₂ as an internal standard, enabling signal self-calibration. This integrated platform allows direct sampling of finger blood without any pretreatment, performing all-in-capillary SERS detection. The proposed method achieves ultrasensitive detection of Alzheimer's disease biomarker Aβ₁₋₄₂, with a wide linear range of 1.0 × 10⁻³ to 1.0 × 10⁻⁷ μg/mL, a low detection limit of 0.089 pg/mL, and satisfactory recovery of 94.3%-101% in human serum. The method was successfully applied to clinical serum samples from Alzheimer's patients and controls of different groups, revealing statistically significant differences in Aβ₁₋₄₂ levels. Furthermore, the results showed excellent agreement with those obtained by the reference ELISA method, demonstrating high accuracy and practical applicability of our assay for early diagnosis and population screening. By combining rational nanozyme design with a miniaturized and calibration-free sampling interface, this work provides a streamlined bioanalytical strategy with great potential for point-of-care testing in early disease diagnosis.