Research On Recyclable SERS-based Immunoassay Technology Based On Fe₃O₄@TiO₂@Ag/Au Composite Nanomaterials

In recent years,with the rapid development of human society,the pace of people's lives has been accelerating and the natural environment has been destroyed to a certain extent,resulting the number of people suffering from cancer to continuous increase.Therefore,it is particularly important for the early diagnosis and treatment of cancer.Accordingly,the development of high-sensitivity and high-specificity immunodetection technology,which efficiently recognize tumor makers specifically expressed in the blood of cancer patients,has become one of the research hotspots in the field of cancer diagnosis and treatment.Among them,Surface-Enhanced Raman Scattering(SERS)has attracted widespread attention from researchers for its unique fingerprint recognition capabilities,single-molecule-level sensitivity,and the ability to achieve in-situ non-destructive testing.In general,the accurate detection results are significantly dependent on the controllable preparation of SERS-active noble metal nanomaterials.However,the complexity and stability of the nanomaterial preparation process with good optical properties have severely restricted its clinical application.By introducing semiconductor materials with photocatalytic activity to construct composite SERS substrate with self-cleaning ability,it can not only relaize the reuse of noble metal nanomaterials,but also facilitate the realization of recyclable immunoassay of tumor markers,which has become an effective solution.Therefore,by designing and constructing multifunctional composite nanomaterials of Fe₃O₄,TiO₂,and noble metals,we systematically studied their structure-dependent catalysis and SERS activity and optimized them,thereby realizing a quantitative recyclable immunoassay with high sensitivity for prostate specific antigen(PSA).The main contents are summarized as follows:1.The recyclable label-free SERS-based immunoassay for PSA based on Fe₃O₄@TiO₂@Ag composite nanoparticles.Firstly,the Fe₃O₄@TiO₂@Ag composite nanoparticles were successfully prepared by the sol-gel and hydrothermal method.The surface morphology,internal structure,components and so on of the composite nanoparticles were systematically investigated by the scanning electron microscope,transmission electron microscope,energy spectrum,and absorption spectrum.Secondly,the correlation between the thickness of the middle TiO₂shell and the areal density of the outside Ag nanoparticles and the photocatalytic and SERS properties of the composite nanoparticles was established.It is revealed that the significant enhancement of photocatalytic performance of TiO₂by Ag is due to the effective inhibition of photogenerated electron-hole pair recombination by the formation of Schottky barrier at the junction.In addition,the aggregation of Fe₃O₄@TiO₂@Ag composite nanoparticles,which caused by the application of an external magnetic field,can enhanced the local electromagnetic field,thereby more hot electrons were excited in TiO₂and the photocatalytic performance was also further improved.Finally,the optimized Fe₃O₄@TiO₂@Ag composite nanoparticles were used to the quantitative recyclable label-free detection of PSA in multiple serum samples.The X-ray photoelectron spectroscopy(XPS)analysis of the immune structures before and after photocatalysis was performed to confirm that the PSA was successfully degraded.Furthermore,the results obtained by using the above-mentioned recyclable label-free SERS-based immunoassay are in good agreement with the chemiluminescence immunoassay(CLIA)method,which shows its good clinical application prospects.2.The recyclable labeled SERS-based immunoassay for PSA based on Fe₃O₄@TiO₂@Au composite nanoparticles and Ag-coated sandpaper.First of all,the Fe₃O₄@TiO₂@Au composite nanoparticles were successfully synthesized by hydrothermal and electrostatic adsorption method.The correlation between the density of outside Au seeds and the photocatalytic and SERS properties of the Fe₃O₄@TiO₂@Au composite nanoparticles was systematically investigated.The optimized composite nanoparticles were served as immune probes.Simultaneously,the Ag-coated sandpaper was prepared by magnetron sputtering,and the correlation between the SERS capability and the mesh of sandpaper was explored.The optimized Ag-coated sandpaper was used as the immune substrate to detect 4MBA,and the limit of detection was achieved to be 0.014 m M.Furthermore,taking the detection concentration of 10^-7g/m L PSA antigen as an example,the optimized immune probe and substrate were used to construct"sandwich"immune structure.It was found that the SERS intensity could still be maintained above80%after six cycles of immunoassay,which revealed that the feasibility of recyclable SERS-based immunoassay for tumor markers.Finally,the“sandwich”immune structure was applied to the quantitative recyclable detection of antigens with different concentrations,and the limit of detection as low as 1.871 pg/m L.