Background-Free Surface-Enhanced Raman Scattering Aptasensor for Ultrasensitive Aβ₄₀ Detection

The quantitative and ultrasensitive detection of amyloid-beta peptides Aβ₄₀ in blood is considered as a powerful strategy for early screening of Alzheimer's disease (AD). In this study, combining dual-aptamer recognition and magnetic-induced enrichment, a background-free surface-enhanced Raman scattering (SERS) platform had been developed for efficient Aβ₄₀ detection. Au@Ag-4-ethynylaniline@Au nanoparticles (Au@Ag-4-EA@Au NPs) had been designed and modified on aptamer2 of Aβ₄₀ to form Au@Ag@4-EA@Au-Apt2 (SERS probe). 4-EA functionalization enables the use of the Raman silent region (1800-2800 cm^-1), thereby minimizing biological interference and avoiding spectral overlapping. The nanogap within gold and silver nanoshells serves as a strong plasmonic enhancer, significantly amplifying the Raman signal and improving detection sensitivity. Aptamer1 of Aβ₄₀ was modified on a streptavidin-modified magnetic bead (SA-MB) to form SA-MB-Apt1 (capture probe). The presence of the target results in the formation of the sandwich structure of SA-MB-Apt1/Aβ₄₀/Apt2-Au@Ag-4-EA@Au NPs. Two Aβ₄₀-specific aptamers ensured precise biomarker recognition and quantification. Magnetic-induced assembly enriches Aβ₄₀ molecules and generates abundant plasmonic "hot spots" through nanoparticle aggregation, resulting in signal amplification. The results demonstrate a remarkable limit of detection of 25 fM (S/N = 3), with a linear range from 10^-1 to 10⁴ pM. This SERS platform provides a robust tool for early AD diagnosis and demonstrates broad potential in clinical molecular diagnostics.