Au Nanocrystal-Modified High-Luminescence NaYF ₄ : Er ³⁺ , Yb ³⁺ Upconversion Nanoparticles for Bioimaging and SERS Immunoassay

Upconversion luminescence (UCL) surface-enhanced Raman spectroscopy (SERS) dual-mode sensing provides an effective strategy for early and precise disease diagnosis due to the synergistic effect of upconversion luminescence imaging and SERS fingerprinting, which enables signal complementation, high specificity, and sensitivity. Herein, NaYF 4:Er 3+,Yb 3+ @Au hybrid nanoparticles (HNPs) were fabricated and employed as UCL-SERS dual-mode sensing materials for the early and accurate diagnosis of gastric cancer. First, by optimizing the concentrations of NaOH, NaF, and NaNO 3, NaYF 4:Er 3+,Yb 3+ UCNPs with intense UCL were successfully prepared. NaYF 4:Er 3+,Yb 3+ @Au HNPs were fabricated by decorating Au nanocrystal (NCs) onto the surface of NaYF 4:Er 3+,Yb 3+ UCNPs. The introduction of AuNCs significantly enhances the fluorescence emission intensity of UCNPs via the localized surface plasmon resonance (LSPR) effect. Meanwhile, the local electromagnetic field enhancement endows HNPs with excellent SERS activity. On the basis of the above dual-mode optical properties, this study realized fluorescence imaging of gastric cancer cells (MGC803 cells) and highly sensitive detection of the gastric cancer biomarker carcinoembryonic antigen (CEA) at low concentrations. Consequently, the UCL-SERS dual-mode sensing platform exhibits great application potential in early and accurate cancer diagnosis.