Fabrication Of SERS Platforms And Its Application On Fast Detection Of Food Contaminants

Surface enhanced raman spectroscopy(SERS), as an emerging analysis technology, has been applied to food contaminants detection since the late 1990 s. However, SERS detection of food contaminant is still in the early stage, especially appling SERS technique to on site fast detection of contaminants in various complex food matrices. In the thesis, with respect to several different food matrices, many SERS detection techniques with few pretreatment steps have been established by developing novel SERS configuration and novel SERS substrates.Firstly, based on the density functional theory(DFT), the geometry optimisation and spectra calculation have been performed on B3 LYP level for thiocyanate, melamine, dicyandiamide, crystal violet and thiram. The results from theoretical analysis were compared with experimental results, and the Raman frequencies and their vibrational modes were assigned according to the visual results.Secondly, for silver colloid, trichloroacetic acid(TCA) was used as a novel aggregating agent to unify the pretreatment process and silver colloid activation process, therefore a simple method was established for detection of sodium thiocyanate in market milk. The limit of detection(LOD) for sodium thiocyanate was 1.45 ppm in milk. During the whole detection process only one agent was used and the detection procedure can be completed in less than 10 minutes.Then, a hydrophobic material, aluminum tape, was employed as support platform to hold sample droplet in SERS detection. The SERS response distributes regularly over the droplet area and represents good reproducibility compared w ith the dried droplet configurations. Furthermore, for real milk sample, based on a particular order of agent addition, melamine and dicyandiamide can be quantitatively detected without any sample pretreatment through an internal standard method, the LODs are 1.40 ppm and 85 ppm respectively. And the detection procedure can be completed in less than 1 minute.Moreover, a novel transparent SERS platform was fabricated via gel-trapping method coupled with liquid/liquid interface self-assembly technique. Gold nanorod was using as building block and the monolayer film of gold nanorod was transfer onto PDMS to fabricate the transparent SERS substrate. The LOD is 0.14 ppm for crystal violet in water using this SERS substrate. Based on the excellent transparency of PDMS, a “Top cover” configuration could be developed for in-situ detection of crystal violet on fish scale.At last, a robust and easy to handle strategy was developed to fabricate silver nanoparticles(Ag NPs) decorated filter paper as surface enhanced R aman spectroscopy(SERS) substrate using dip-coating method. Filter paper was modified with chloride ions for chemisorption of Ag NPs, overcoming the electrostatic repulsion between Ag NPs and paper. Excellent uniformity and reproducibility of this substrate are guaranteed by the self-assembly mechanism. The absorbency and capillary action of the paper based SERS substrate enables efficient collection and detection of thiram in complex area on vegetables. The whole SERS detection procedure can be completed in less than 1 minute.