Synthesis And Sensor Application Of Magnetic Surface-Enhanced Raman Scattering Nanocomposites

Because of its unique fingerprint spectrum,rapid nondestructive detection and high sensitivity,Surface-Enhanced Raman Scattering(SERS)has been widely used as a powerful analytical technique in molecular detection,bioimaging,diagnosis,reaction monitoring,etc.The traditional SERS platform based on metal nanoparticles can no longer meet the growing demand for analysis.Magnetic plasma nanocomposites have become new research hotspots.Therefore,the preparation of magnetic SERS substrate is very important,especially,the sensitivity and repeatability of substrate are still facing some challenges.In this paper,a series of cubic magnetic SERS active substrates with high sensitivity and good repeatability had been prepared and their applications in sensors had been explored.The details were as follows:1.Uniform cubic Fe3O4@SiO2@Au@Ag nanoparticles with superparamagnetism and good dispersion were synthesized for the first time.First,the synthesis conditions of α-Fe2O3 with single cubic morphology were investigated.Second,the Stober method was improved to synthesize α-Fe2O3@SiO2.Third,α-Fe2O3@SiO2 was calcined in a hydrogen atmosphere of 360 ℃ to obtain Fe3O4@SiO2.The SiO2 shell not only protected the regular cubic morphology,but also provided a strong framework for further loading Au@Ag nanoparticles.Fourth,a multifunctional self-assembling PEI shell was formed on the surface of Fe3O4@SiO2.The PEI layer prevented the aggregation of Fe3O4@SiO2 particles,maintaining good magnetism.There is a large amount of NH2-on the surface of Fe3O4@SiO2 nanoparticles modified by PEI.Au@Ag was densely loaded on the Fe3O4@SiO2 nanoparticle through N-Ag bond.The composites were systematically characterized by SEM,XRD,TEM,element mapping and energy spectrum.By the detection of PATP,CV and Thiram,Fe3O4@SiO2@Au@Ag showed excellent SERS activity,good repeatability and the obvious enhancement of SERS signal by magnetic aggregation as expected.2.The cubic Fe3O4@SiO2 nanoparticles were coated with the mesoporous TiO2 layer and the magnetic Fe3O4@SiO2@mTiO2 nanoparticles with needle-like surface were prepared.Due to the sharp structure on the surface,more hot spots might be generated to enhance SERS signal.The synergistic enhancement effect was studied by combination of Fe3O4@SiO2@mTiO2 nanoparticles and Au@Ag sol.Fe3O@SiO2@mTiO2/PATP nanoparticles could capture TNT because the charge transfer process from the electron-rich amino group of PATP to the electron-deficient aromatic ring of TNT.When Fe3O4@SiO2@mTiO2/PATP was mixed with Au@Ag,the electron resonance PATP-TNT complex largely lit up the SERS signal in the presence of trace TNT.The detection limit of TNT was 10-12 M in deionized water.The SERS sensor could be applied to detection of trace TNT in lake water and liquor system and it had potential practical application.3.A uniform non-agglomerated cubic Fe3O@TiO2@Au SERS active substrate was prepared,which could be used for sensitive detection,simple operation and photo degradation of toxic benzidine and phenol derivatives.Different from the previous method of coating TiO2,the traditional sol-gel method was extended.TBOT was used as the precursor of hydrolysis and condensation reaction in the mixture of ammonia water and ethanol.The hydrolysis condition was studied and the hydrolysis rate was controlled reasonably.It could promote heterogeneous nucleation and avoid more in-phase growth,so that Fe2O3@TiO2 remained original cubic shape.Fe3O4@TiO2 was prepared by H2 reduction at high temperature and further functionalized by APTMS.The surface of Fe3O4@TiO2 was covered with a dense layer of Au particles by strong chemical interaction between exposed N12-and Au.The target molecule was captured by the azo coupling between PATP and benzidine or phenol derivative.The azo products could bind to Fe3O4@TiO2@Au SERS substrate by SH group.Because the azo products had special SERS fingerprints,the toxic molecules of benzidine and phenolic compounds could be identified.In addition,the degradation of azo compounds was achieved by TiO2 assistance and plasma-enhancement of photo catalysis.