Surface Modification Of Silver Nanoparticles And The Study On Its SERS Performance

For high-precision biochemical sensing,surface-enhanced Raman spectroscopy?SERS?has been demonstrated to be a highly sensitive spectroscopic analytical method that has shown promising applications in biomedical science,material science,food inspection and environmental monitoring.With the development of nanotechnology,metal nanoparticles?NPs?substrates with adjustable surface plasmon resonance have attracted much attention,and the preparation of the SERS substrate with good performance is one of the most important research field in SERS technology.In this thesis,silver nanoparticles?Ag NPs?were deposited on silicon wafer and the SERS activity of Ag NPs array was investigated.The surface modification of Ag NPs was applied to improve the stability of Ag NPs substrate,and the effect of surface modification on the stability of Ag NPs substrate was studied by the application of the core-shell structure.Silica film as well as the Parylene-C film are deposited on the Ag NPs substrate to fabricate the core-shell structure,and the result indicated that the stability of the Ag NPs substrate was enhanced by the core-shell structure significantly.In this paper,the nanomaterials were briefly introduced.The parameters of sputtering and thermal vacuum annealing processes were investigated to obtain the Ag NPs array that possessed the uniform particle size distribution and dense nanoparticle arrangement.SERS characterization of the Ag NPs substrate was performed by crystal violet?CV?molecules,which acted as the probes.The enhancement factor of the Ag NPs substrate here was calculated and the result is 2.15×106.Inductively coupled plasma-enhanced chemical vapor deposition technology was employed to deposit the SiO₂ film,and the two-dimensional Ag@SiO₂ core-shell substrate with different thicknesses of silica were prepared.SERS characterization of the Ag@SiO₂ substrate was performed by CV molecules.The results showed that the SERS activity of Ag@SiO₂ substrate increases first and then decreases with the increase of the layer thickness of silica.At the thickness of 10 nm,the SERS activity of Ag@SiO₂ substrate was the strongest and the enhancement factor could reach to 6.62 × 106,the detecting limit of CV molecules could reach 10-10 M.On this basis.The stability analysis was conducted by soaking substrates that coated with and without the silica layer into the deionized water for different time.The results showed that the stability of the Ag@SiO₂ substrate can be extended from 0.5 h to 24 h when immersed in the aqueous solution,and the attenuation on SERS activity of the Ag@SiO₂ substrate after soaking for 72 h is less than 25%.Parylene-C was then deposited on the Ag NPs substrate to deal with the poor reusability of the Ag@SiO₂ substrate.The deposition process of Parylene-C layer with different thickness was described in detail and the effects of coating thickness on stability as well as the SERS activity of Ag@Parylene-C substrate were investigated.On this basis,a kind of simple microfluidic channel structure was fabricated and then integrated with the Ag@Parylene-C substrate to test the SERS activity and stability of the substrate in the liquid phase environment.It is found that the Ag@Parylene-C substrate with a thickness of 100 nm showed the fine coating effect and high SERS activity.After integrated with the microfluidic channel structure,the detecting limit of CV molecules that absorbed on Ag@Parylene-C substrate could reach 10-10 M,and the reused times of the Ag@Parylene-C substrate can be extended from 20 to 500.After the 500 testing experiments,the attenuation on SERS activity of the Ag@Parylene-C substrate is less than 10%.The result indicated that the Ag@Parylene-C substrate can be the candidate for the in-situ microfluidic SERS biochemical sensing application.