Quantitative and Recyclable Surface-Enhanced Raman Spectroscopy Immunoassay Based on Fe₃O₄@TiO₂@Ag Core–Shell Nanoparticles and Au Nanowire/Polydimethylsiloxane Substrates

Quantitative immunoassay of specific tumor markers in clinical serum is critical for early monitoring and treatment of cancer. Herein, a surface-enhanced Raman scattering (SERS)-active immunostructure, consisting of Fe3O4@TiO2@Ag core–shell nanoparticles as immunoprobes and Au nanowires (NWs)/polydimethylsiloxane (PDMS) film as the immunosubstrate, was proposed for the quantitative determination of prostate-specific antigen (PSA) and α-fetoprotein (AFP). In this method, the ultrasensitive detection of the two tumor markers could be achieved in parallel on the curved flexible AuNWs/PDMS substrate. A recyclable detection with limit of detections (LODs) of 0.49 pg/mL for PSA and 0.72 pg/mL for AFP could be realized, attributing to the excellent photocatalytic property and magnetic separation of Fe3O4@TiO2@Ag core–shell NPs. Moreover, improved linear relationships with R2 values of 0.986 and 0.996 in the detection were perfectly obtained by utilizing the intrinsic SERS peak of PDMS as an internal standard (IS). In addition, the trace two antigens of PSA and AFP in serum samples of cancer patients were monitored using the developed immunoassay protocol, which shows superiority than chemiluminescent immunoassay (CLIA). Such a novel quantitative and recyclable SERS-based immunoassay would provide an alternative reliable method for the early accurate diagnosis of cancer.