2 Composite Microspheres Preparation And SERS Performance Precious Metal / TiO

Surface enhanced Raman scattering (SERS) has attracted widespread application inbiomedicine, molecular recognition, biosensing, environmental monitoring, surfacescience, and residual pesticide in food, as it possesses the merits including sharpbandwidth, high sensitivity, anti-photobleaching, as well as the ability of in-situ andnoninvasive analysis for diagnosis and bioassay.In this paper, the hierarchical TiO2/Ag microspheres and Au/TiO2hollowmicrospheres were synthesized with a bottom-up strategy. Combined with SEM, TEM,BET, TG, XRD, Raman, FT-IR and XPS technique, the structure characteristic, SERSperformance, and enhancement mechanism were systemically researched. In addition,the above two composites were explored in the field of chemical reaction and immuneprotein monitoring as well, respectively.The main contents of this paper are as follows:(1) The hierarchical TiO2/Ag microspheres were synthesized via the followingsteps. The TiO2microspheres assembled with nanosheets were synthesized throughsolvothermal method, in which tetrabutyl titanate acted as Ti resource, isopropylaminewas structure-directing agent and isopropyl alcohol played a role of agent. The Ag/TiO2microspheres were then prepared via in-situ reduction and growth method, in whichAgNO3and glucose were used as the source of silver and reducing agent, respectively.The SERS performance of TiO2/Ag microspheres was studied with4-aminothiophenol(4-ATP) for the SERS probe molecule. The results of SERS revealed that the detectionlimit can reach10-7mol/L, due to the the interfacial couple action bentween Ag andTiO2. In addition, the TiO2/Ag microspheres were employed for direct and label-freemonitoring of the Ag-catalyzed reduction of4-nitrothiophenol (4-NTP) to thecorresponding aniline derivative (4-ATP), in which the obtained TiO2/Ag microspheres acted as the role of catalyst and SERS basement, while sodium borohydride wasreducing agent.(2) Au/TiO2hollow microspheres were synthesized via the following steps. C@Aucolloidal spheres were prepared by in-situ reduction and growth method, in which thecarbon spheres as templates, HAuCl4as Au resource, and glucose as reducing agent.Au@TiO2hollow microspheres were then prepared via the coating of titania sol andconsequent calcinating in air. The results of SEM, TEM and XRD revealed thatAu@TiO2hollow microspheres with an average diameter of400nm were synthesized;and Au nanoparticles with an average diameter of10nm uniformly distributed inside ofmicrospheres. The hollow microspheres are subsequently tagged with Raman probemolecules (4-ATP) via siphonage effect, and strong covalent Au-s bonds form betweenAu and4-ATP. We systematically investigated the SERS properties of Au@TiO2hollowmicrospheres. The results presented that the detection limit of SERS was as low as10-10mol/L and enhancement factor was5.4x105. By constructing"antibody-antigen-antibody" detection system via glutaraldehyde crosslinking method,human IgG immunoglobulin was successfully detected, with the Au@TiO2hollowmicrospheres acting as the label material.