Super-stable, Highly Sensitive Surface-enhanced Raman Spectroscopy Of Silver Substrate Preparation And Application

Surface-enhanced Raman scattering (SERS) Spectroscopy has shown the advantage of overcoming the low sensitivity of conventional Raman spectroscopy and molecular detection capabilities. The metal nanoparticles which is used SERS substrates widely, is dif?cult to control the size of the resulting colloids and the degree of the aggregation with colloid ageing. Particularly, after the addition of the analyte, the aggregation of metal colloids trends to coagulate. So the reproducibility of SERS signals is too poor to be applied for quantitative analysis. In this work, we use an economical and'green'reagent - phytic acid(IP6), IP6 and its salts are liable to chelate with metal ions because of its structure containing six phosphates separately on both sides of the cyclohexane. On the other hand, IP6 molecules can form into the micelle themselves and some free phosphates remaining on the outside of the micelle. IP6 micelles acted as a soft template and stabilizer in the process of synthesis.The IP6 micelles acted as a soft template, and tri-sodium citrate was used as the reduction regent to synthesis the Ag nanoparticles. The Uv-vis Spectra show the growth of the of Ag nanoparticles. The transmission electron microscope (TEM) images show the effect of the IP6 micelles, and the IP6 micelles break-up at last. The IP6 molecules formed into the micelles again and the as-made silver nanoparticles were immobilized effectively by phosphates in the outer layer of the micelle. The SERS spectra indicated that this kind of Ag nanoparticles could provide reproducible and ef?cient surface enhanced Raman signals within 4 months.Using IP6 micelles as a template, L-ascorbic acid which has stronger reduction abilities acts as the reduction regent to synthesis the Ag nanoparticles. The Uv-vis Spectra show the synthesis process ended within 10min. when the reduction regent is insufficiency, the TEM images show the morphology is core-shell structure. There is no"hot spot"which is crucial to the SERS activity because of such thick IP6 shell. No SERS signal from the Rhodamine 6G (R6G) which is used as the probe molecular. But this structure can give rise to surface enhanced ?uorescence (SEF) . If the reduction regent is sufficiency, the IP6 shell turn thinner, and the gap between Ag nanoparticles is about 2nm, which exhibit the high efficient SERS enhancement for R6G molecules. The Raman enhancement factors (EF) is about 108. But the ?uorescence is quenched.One of the most commonly methods for synthesizing Ag–Au alloy nanoparticles is the replacement reaction between Ag nanoparticles and HAuCl4. We know that small Ag nanoparticles (<10 nm in the current case) can increase the interdiffusion rate of the alloying between Au and Ag atoms. With different dosage of HAuCl4, the surface plasmon resonance (SPR) is tunable. The energy disperses X-ray (EDX) spectra show the element of the products. The TEM image shows the structure of the product when the dose of HAuCl4 is 2mL is cauliflower-like. The high-curvature feature of the cauliflower-like structure surface and the roughness increasing can be in favor of the adsorption of the molecules for SERS detection. The cauliflower-like structure is a whole particle and stabilized by the IP6 micelle. The reproducibility of the SERS signal is good (>6 months).IP6 micelles act as templates to prepare Ag nanoparticles. The Ag nanoparticles to react with different amount of HAuCl4 to synthesis Ag–Au alloy nanoparticles. From the Uv-vis spectra, we can find that the surface plasmon resonance (SPR) is tunable. The TEM images show the roughness of the surface is high, and there are many"hot spots"which is crucial to SERS activity. Use the R6G is the molecular to investigate the SERS activity primary. The SERS spectra show different product has different SERS activity. To confirm the effect of the IP6 micelle existence on the synthesis, we demonstrate the comparative experimental results obtained at the same conditions in the absence of IP6 micelles. The results show that the SERS activity is lower if the IP6 micelles do not act as the templates in synthesizing the Ag nanoparticles.