Recyclable label-free SERS-based immunoassay of PSA in human serum mediated by enhanced photocatalysis arising from Ag nanoparticles and external magnetic field

In the field of SERS-based immunoassay, the recyclable utilization of noble metal materials is essential for their practical application in clinical medicine. Herein, a kind of novel multifunctional Fe3O4@TiO2@Ag microparticles (MPs) was synthesized through a poly-step reaction, and then their feasibility for recyclable label-free SERS-based immunoassay of prostate specific antigen (PSA) was demonstrated. The photocatalytic efficiency of the Fe3O4@TiO2@Ag MPs was fully adjusted by tuning the thickness of the middle TiO2 shell and the areal density of the outside Ag NPs. Particularly, the Fe3O4 core played a critical role in further improving the photocatalytic activity under external magnetic field. Thereafter, the successfully photocatalytic degradation and recyclable detection of PSA in human serum was confirmed by the change of O 1s, N 1s, and C 1s signals in the XPS characterization and a limit of detection as low as 16.25 pg/mL was realized. Furthermore, the quantitative recyclable detection of PSA in clinical serum samples with prostate cancer was conducted, and the results are basically consistent with those of the traditional chemiluminescent immunoassay, showing small relative deviation less than or equal to 5.7%.