Preparation And Detection Applications Of SERS-active Substrates

Surface enhanced-Raman scattering (SERS) as a powerful spectroscopy technique provides non-destructive and ultrasensitive characterization. Because of many potential applications in electrochemistry, analytical chemistry, biophysics and medicine and so on, the study of SERS substrates have elicited increasingly scientific and technological interests. Yet, the stability, repeatability and sensitivity of SERS signals are easily affected by surrounding environments. This dissertation presented here is focused on the fabrication of various active-SERS substrates, the application of quantitative detection of harmful compounds and rapid detection of intermediate compounds, and effect of magnetic fields on SERS. The main parts of the results are summarized below:1. Au nanoparticles (NPs) forming Au shell are coated on the surfaces of Ni microparticles (MPs) through a simple redox-transmetalation reaction, forming Ni/Au core-shell MPs. Then Au hollow spheres (HSs) are prepared by etching the Ni core in1mol/L HC1solution. Surface-enhanced Raman Scattering (SERS) spectroscopy signals of typical analytes such as rhodamine6G (R6G) are observed on micro-scale Au HSs, even though the concentration of the analyte is as low as10-8mol/L (R6G). The Au HSs are also applied to detect tetracycline (TC), and strong SERS signal is observed with the TC concentration of0.1μg/L. The quantitative analysis can be performed at1595and1320cm-1, and a good linear response is also obtained. This work provides a potential and unique technique to detect broad-spectrum polyketide antibiotic in future, and the detection of TC in foods and milk can also be performed using this SERS-based Au HSs substrate, which will benefit human health.2. The development of ultrasensitive and rapid methods for the detection of Sudan Ⅳ, a coloring agent for commercial applications including foodstuffs, is becoming increasingly important. This paper reports the result of an investigation on surface-enhanced Raman spectroscopy (SERS) based ultrasensitive detection of Sudan IV using Au hollow spheres (HSs) immobilized Cu foil substrates. The strong SERS effect resulting from the particle-particle and particle-substrate plasmonic coupling is optimized by manipulating the process of preparation and forming a stable arrangement. The correlation between the intensity of SERS diagnostic band and Sudan Ⅳ concentrations is shown to exhibit three linear regions, which are applied to the determination of Sudan Ⅳ in chili samples. The SERS analysis reveals the existence of Sudan Ⅳ in chili samples at the magnitude level of10-5g/kg, while the result from liquid chromatography-mass spectrometer (LC-MS) shows that the concentration of Sudan Ⅳ in chili samples is0.95*10-5g/kg, close to the value calculated by SERS. However, although the two results are close, the problems placed at the quantitative study of SERS technique still exist. Sensitivity is still in need of improvement. For now, it can be seen that single SERS method as a direct detection technique has the potential to develop the detection of Sudan Ⅳ.3. ZnO/Ag seaurchin-like hybrids were prepared through the reaction of zinc salts with KOH to form ZnO particles, followed by deposition of Ag nanoparticles (NPs) on the surface of the particles. With the time of this photochemical deposition reaction extended from0.5h,2h to8h, the size of Ag NPs is from11nm,19nm to29nm. Due to high surface-to-volume ratio, rich surface tips, and open morphology, ZnO/Ag seaurchin-like hybrids are expected as effective Raman substrates. It is shown that the materials have high sensitivity, and well reproducibility. After calculation, the enhancement factor values for R6G molecules on ZnO/Ag are3*106in peak1360cm-1and2.98*106in peak1575cm-1, respectively. And the maximal value of relative standard deviation is to be below0.15. It is suggested that local electric fields caused by the electron transfer between ZnO and Ag,"echo effect" and a high aspect ratio between ZnO branches and Ag NPs co-contribute to SERS enhancement. This distinct morphology of ZnO/Ag seaurchin-like hybrids should also make them ideal substrates to load various large molecules for SERS-based sensing and characterization. Based on ZnO/Ag seaurchin-like hybrids, we fabricate ZnO/Ag-Pd seaurchin-like hybrids and use it as SERS substrates and catalyst to detect the possible intermediates of Suzuki reaction. The initial result shows the existence of intermediates.4. Currently, because of the wide use of magnetic/metal hybrid materials in the field of surface-enhanced Raman scattering (SERS), magnetic fields (MFs) as a kind of surrounding environments of SERS substrates have been not ignored. And enormous attentions for the effect of MFs on SERS are very necessary. Our analysis from previous reports shows SERS signals are closely associated with MFs; yet the study of the exact effect of MFs on SERS is still in need of detail and broadening. In this work, we demonstrate that the use of Ni/Au microparticles (MPs) and Au hollow spheres (HSs) to study the effect of MFs on SERS signals. The experiments are preformed from three aspects, including the comparison of SERS signals of Ni/Au MPs with different Ms values, the comparison of SERS signals of Au HSs and Ni/Au MPs under different external MFs, and the comparison of SERS signals of single Au HS particle and single Ni/Au particle in the absence and presence of an external MF. Thereinto, under different external MFs from0,0.01,0.02,0.04to0.08T, SERS signals of Au HSs and Ni/Au MPs are gradually weaker. According to the experiments, the weakening effect of MFs on SERS is confirmed and it is suggested that the weakening effect is originated from the blue-shift of surface plasmon resonance. Theoretical calculation shows that the locking of charge-transfer from Au to probe molecules leads to the weakening effect of MFs on SERS.