| Surface-enhanced Raman spectroscopy(SERS)with high selectivity,super-sensitivity,nondestructive and rapid performances has been regarded as a powerful technique for the detection of trace chemicals and biomolecules.To obtain enhanced and reproducible SERS signal,an effective substrate with good enhancement ability as well as reproducible and robust characters is very important.Titanium dioxide(TiO2)is a widely studied semiconductor due to its good physical and chemical stability.Although the importance of TiO2 nanomaterials in SERS has been confirmed,its efficiency depends on surface area,crystal structure,shape,size,energy band and the crystallinity of the loaded noble metals.TiO2 nanostructures with different morphologies and nanocomposites based on TiO2 have attracted much attention due to their different physical and chemical properties.TiO2 with nanoarray morphology(TNA)could increase the number of adsorbed molecules by high surface area and enhance the sensitivity of SERS detection.Meanwhile,the ordered array structure of TNA has strong advantages in signal uniformity and repeatability.However,the SERS sensitivity of pure TNA was not high and the band gap of TiO2 was wide.Combining noble metal nanoparticles such as Ag nanoparticles with TiO2 could overcome these shortcomings of TiO2.Due to the synergy of plasma and charge transfer(CT),Ag/TiO2 composite material has strong light capture and SERS performance.Therefore,in this paper,TiO2 nanoarrays were prepared by simple hydrothermal method,and SERS enhancement strategies were explored for Ag nanomaterials with different morphologies and/TNT composite to form substrates.The main contents are as follows:Part One:Research on the in-situ preparation of AgNPs/TNA nanocomposites and Surface Raman Enhancement PerformanceUniform and independent rutile TNA was grown on the conductive surface of conductive glass(FTO)by hydrothermal reaction.Silver nanoparticles(AgNPs)were photochemically grown directly on the surface of TNA layer by uv irradiation of AgNO3 solution.The physical properties of AgNPs/TNA substrates were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and UV-Vis.SERS enhanced performance of AgNPs/TNA substrate was investigated with rhodamine 6G(R6G)probe molecule.When the concentration of AgNO3 was 1 mM and the uv irradiation time was 30 minutes,the SERS activity of the prepared AgNPs/TNA composite was the strongest,and the lowest concentration detected for R6G was 10-7 M.The SERS detection application of AgNPs/TNA substrate showed high reproducibility and recyclability.Part Two:Preparation of AgNTs/TNA composites and its application in the detection of food additivesSilver triangular nanoparticles(AgNTs)were prepared by epigallocatechin gallate(EGCG)assisted green reduction method.They were compounded with TNA to construct SERS substrate of metal/semiconductor composites based on TNA.The physical properties of AgNTs/TNA substrates were characterized by SEM,Transmission electron microscopy(TEM),XRD and UV-Vis.The detection effects of the substrate on R6G,crystal violet(CV),malachite green(MG)and Thiram(Thiram)were investigated.The results showed that the minimum concentrations of these four substances were 10-10 M,10-9 M,10-8 M and 10-7 M,respectively.The AgNTs/TNA substrate has a low detection limit,good reproducibility and uniformity,and has a good application prospect in food sample detection.In addition,the reusability of the AgNTs/TNA substrate was investigated.The substrate can still be used for detection after being cleaned 3 times by ultraviolet light.Part Three:Preparation of hydrophobic SERS substrate based on AgNTs/TNA composite and its application in the detection of food additivesLong chain alkyl mercaptan molecules with low surface energy properties were modified onto the surface of AgNTs/TNA substrate by dodecyl mercaptan(DM)self-assembly method,forming a SERS detection substrate with hydrophobic properties.The physical properties of AgNTs/TNA substrates were characterized by infrared spectroscopy(FTIR)and contact Angle techniques.The effect of DM concentration and self-assembly time on SERS performance of substrate was studied.The experimental results showed that 10-3 M DM was used as the modified molecule,and the SERS signal obtained after 2 hours of assembly was the strongest.The lowest concentrations detected by R6G,CV and MG were as low as 10-11 M,10-11 M and 10-9 M,respectively.The results showed that the hydrophobic interface formed by self-assembled mercaptan molecules could enrich the molecules to be measured,increase the number of molecules to be measured per unit,and then enhance SERS signal,which has great application potential in actual sample detection. |
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