Dual-modal immunoassay for prostate cancer-derived exosomes enabled by a black phosphorus/silver SERS substrate and Yb/Er co-doped NaGdF4 UCL nanoprobes.

Exosomes are regarded as cancer-associated biomarkers for early diagnosis and prognosis in clinical bioassays. Nevertheless, it remains a challenge to develop an approach that can achieve ultra-sensitive and quantitative detection of exosomes. Herein, an innovative dual-mode immunoassay dependent on surface-enhanced Raman scattering (SERS) and upconversion luminescence (UCL) was developed to detect prostate cancer-derived exosomes. A novel SERS-active immunosubstrate was constructed by combining black phosphorus (BP) with Ag nanoparticles, which exhibited an enhancement factor (EF) of about 3.69 × 10⁹, due to the synergistic electromagnetic and chemical effects. Meanwhile, an immunoprobe with stable and visually distinguishable UCL was developed based on Yb/Er co-doped NaGdF₄ nanoparticles with an intrinsic two-photon process. The specific capture of exosomes was achieved through antigen-antibody binding within the sandwich immunostructure, achieving limits of detection (LOD) as low as 93 and 172 particles/mL based on the dual-modal detection, respectively. Furthermore, the recognition of different derived exosomes was simply realized by visually observing the green fluorescence with different intensities, which paves the way for efficient preliminary identification of prostate cancer. Finally, the validation with clinical serum samples proved that the proposed approach holds significant promise for rapid cancer screening and diagnosis.