The SERS Properties Of Au-Ag Core Shell Nanorods And Their Application In In-situ Bacteria Differentiation

In-situ detect single bacteria on surface in an effective and efficient way is of great significance in field such as diseases diagnoses and prevention,deal with the emergency public health and safety incidents.Surface enhance Raman scattering(SERS)posses several merits such as no need for labeling,fast and no destructive,multiplex capability.It can provide fingerprint information from the internal of matter itself and is very suitable for in-situ bacterial differentiation.Up to now,utilize SERS for lable free bacterial detection either through premixing the bacteria suspension with colloidal noble particle,or dropwise bacteria suspension onto premade SERS substrate.These methods require for pretreatment of the bacteria and have limited scope of application.Due to the weak adhesion between SERS substrate and bacterial cell wall or limited sensitivity,There are only few reports focusing on in situ bacteria detection.Based on the above reasons,positive charged Au-Ag core shell nanorods(Au@Ag NRs)which posses higher SERS efficiency were synthesized and successfully applied for in-situ bacterial differentiation on silicon and filtering layer of the face mask surface.The main research contents of this thesis are as follows:(1)6 kind of Au nanobypyramids(Au NBPs)and 5 kind of Au@Ag NRs were synthesized through thermally treated gold seeds.There morphology,crystal structure as well as dispersibility were fully investigated through Scanning Electron Microscopy,Transmission Electron Microscopy,X-Ray Diffraction,and Dynamic Light Scattering Particle Size Analyzer.The correlations between their optical property and aspect ratio were also investigated.We find their absorbance spectrum show extremely narrow half peak width,and their absorbance peak can be tuned from visible to near infrared.(2)The SERS enhancement performance of Au NBPs and Au@Ag NRs with different aspect ratio was analyzed using 4-MBA and R6G as probe molecule.We found the SERS enhancement factor of Au@Ag NRs,whose absorbance peak lie in the range around 785 nm and have 3.5 times aspect ratio,were 11.0 times higher than Au NBPs.At the same time,the surface electromagnetic field distribution as well as scattering spectrum were simulated through the finite difference time domain technique.The enhancement factor from single Au@Ag NRs was calculated to be 9.85×10~7.(3)S.aureus and E.coli were used as the research objects for SERS in situ identification.Due to the electrostatic interaction and hydrophobic force,Au@Ag NRs 3 were highly concentrated on the the bacteria cell wall,which layed a solid foundation for acquiring high quality SERS signal.Afterwards,SERS spectrum as well as SERS mapping were acquired from single bacterial from different position on silicon wafer and filtering layer of the face mask surface.We also established a model by principle component analysis-linear discriminant analysis and successfully achieved bacteria in situ differentiation.