Tri-mode sensing of Alzheimer’s disease biomarkers mediated by sophisticated Yb/Er co-doped NaGdF4@Au nanocomposites with surface enhanced Raman scattering/up-conversion luminescence/magnetic resonance properties

Multi-modal sensing techniques based on versatile optical nanocomposites have advanced rapidly, enabling fast and precise diagnosis of biological substances with high sensitivity and resolution. In this study, Yb/Er co-doped NaGdF₄@Au nanocomposites were synthesized using an efficient electrostatic attraction strategy facilitated by surface modification. The quantity of sensitizing Yb ions and the incorporation of Au nanoparticles (NPs) were identified as crucial factors influencing upconversion luminescence (UCL). Notably, concentration-dependent magnetic resonance imaging (MRI) was demonstrated for the Gd-participated nanocomposites, allowing for dual-mode bioimaging of brain neuroma cells. Attributed to the enhanced localized electromagnetic field generated by the Au NPs assembled on the NaGdF₄ matrix, surface enhanced Raman scattering (SERS) were further obtained from the nanocomposites, which demonstrated reliable sensitivity, reproducibility, homogeneity, and stability. Consequently, the proposed nanocomposites were employed in a typical sandwich immunoassay for Amyloid-beta 42, based on a linear dose–response curve established through SERS modality. This multi-modal sensing platform holds significant potential for diverse clinical biomedical diagnostics.