Dissertation > Mathematical sciences and chemical > Physics > Optics > Spectroscopy > Various types of spectroscopy

Preparation of Surface-enhanced Raman Scattering Substrates and Its Application in Dairy Products

Author JinChaoYing
Tutor HaSiWuLiJi
School Harbin Institute of Technology
Course Physical Electronics
Keywords Surface enhanced Raman spectroscopy (SERS) gold colloid silver colloid melamine sodium thiocyanate (NaSCN)
CLC O433.5
Type Master's thesis
Year 2012
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Surface enhanced Raman spectroscopy (SERS), coupled with nanotechnology isa new spectroscopic technology, and for its rapidity, accuracy, ultra-sensitivity andrepeatability, has been utilized in medicine, pharmacology, archaeology, and materialsscience etc. fields, meanwhile, it demonstrate great advantages in trace analysis,qualitative and quantify analysis. In these years, with the arise of food contaminations,SERS begin to apply in food safety detection. For the core role of SERS-activesubstrates and its selective enhancement, the preparation of SERS-active substrates withsharp enhancement, high-stability and repeatability lie the heart of the application ofSERS in food contaminations detection, thus the method that can product suitablesubstrates for the food safety detection using SERS need to study.The addictive in the dairy product is the main study objective of this paper, goldand silver colloids were produced by a hydrothermal citrate-reduction method, and itsUV-Vis absorption were detected, the results demonstrate that both the colloids particlesare mainly consist of sphere, with good distribution of particle size and single range.First, the surface enhanced Raman spectroscopy of the antiseptic sodiumthiocyanate (NaSCN) and the prohibited additive melamine in the milk are detectedwith the obvious signal, using the gold colloid as the SERS substrate. Compare thenormal Raman and the surface enhanced Raman spectroscopy of the powder andaqueous solution of NaSCN and melamine, and then the characteristic Raman peaks ofthe obtained spectroscopy for the qualitative analysis are identified. The goldnanoparticles of different sizes are prepared, afterwards the influence of the size of thegold nanoparticles on the SERS signals of the adsorption; the influence of the amount ofadsorption on the SERS intensity are discussed, through changing the mixing proportionof the NaSCN aqueous solution (the same concentration) with the gold colloid; the veryproportion with the highest enhancement are found and compared. The same studyprocesses are made to all the solution with different concentration. The influences of theexperiment condition such as temperature and the PH on the SERS signal intensity ofthe gold colloid are researched, the optimum external condition, which can make theSERS signals of the adsorption in the gold colloid to be the strongest, is obtained.Meanwhile a series of SERS detections of melamine and NaSCN aqueous and milksolution are obtained with the substrate of gold colloids and the results demonstrate thatthe limit of detection (LOD) of SERS for melamine and NaSCN are very near to thenational testing standards. The aqueous solution of NaSCN and melamine of quite lowconcentration are detected using SERS technology coupled with the gold colloids as the active substrates, additionally the Raman peaks of the melamine milk solution with verylow concentration can be detected too.Secondly, using silver colloid as the SERS-active substrate, the surface enhancedRaman spectroscopy of the NaSCN aqueous solution is studied. The influence of theamount of NaSCN on the SERS signal was discussed, the very proportion with thehighest enhancement are found. The influences of the experiment condition such astemperature and the PH on the SERS signal intensity of the silver colloid are researched,and the optimum external condition, which can make the SERS signals of theadsorption in the gold colloid to be the strongest, is obtained.Then the influence of chloride ion on the SERS signal of sodium thiocyanate isdiscussed. The consequences show that for different SERS substrates the enhancementeffects are different. For the silver colloid, the addition of chloride ion will active thesilver nanoparticles and strengthen the SERS signals obviously; while for the goldcolloids the addition doesn’t stimulate the nanoparticles, but quench the SERS signals.

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