| Raman spectroscopy is a versatile tool to gain structural information of complexmolecules under in situ conditions. The intrinsically low Raman signal intensity canbe great enhanced for molecules attached to metallic/plasmonic surfaces by theinteraction of the oscillating electric field of the radiation and the surface plasmons ofthe metal. The resultant surface enhanced Raman phenomenon is associated with anincreased sensitivity, which is enhanced up to10-14orders of magnitude overconventional Raman spectroscopy. Thus surface enhanced Raman spectroscopy(SERS) is a desirable technique to selectively probe trace amounts of analyte in manykinds of system. SERS as an ultrasensitive detection method, has great potential forchemical and biological sensing and imaging applications not only because it isselective and sensitive, but also because it gives little interference from water. Inaddition, since Raman spectra are dominated by the characteristic vibrationalfingerprint of the target molecules SERS offers great advantages when it is applied tostudy complicated systems. Compared to fluorescence spectroscopy, Raman bands aremuch narrower than fluorescence emission bands. Thus, based on the unique Ramansignature of each molecule, SERS can be applied for the detection of several targets atthe same time. Due to its high surface sensitivity and discrimination ability SERScould be a promising analytical method for food safety analysis, drug analysis,explosive detection and environmental pollutant monitoring. However, for different target, differentstrategy of SERS method should be designed and conducted. Thefollowing parts which is included in the thesis, demonstrates how to apply a SERSmethods for hazard detection:(1) Ultrasensitive trace analysis for2,4,6-trinitrotoluene using nanodumbbellsurface-enhanced Raman scattering hot spotsWe develop an ultra-sensitive surface-enhanced Raman scattering (SERS)-baseddetection system for2,4,6-trinitrotoluene (TNT) using nano-dumbbell structuresformed by the electrostatic interaction between positively and negatively charged goldnanoparticles. First, Meisenheimer complexes were produced between TNT andL-cysteine on gold substrates, and4-mercaptopyridine (4-MPY) labeled goldnanoparticles (positively charged) were allowed to interact with the Meisenheimercomplexes through the electrostatic interaction between the negatively chargedaromatic ring of the complex molecules and the positively charged nanoparticles.Then, negatively charged gold nanoparticles were added in order to formnano-dumbbells. As a result, many hot junctions were generated by thedumbbellstructures, and the SERS signals were greatly enhanced. Our experimental resultsdemonstrate that the SERS-based assay system using nano-dumbbells provides anultra-sensitive approach for the detection of TNT explosives. It also shows a strongpotential for broad application in detecting various explosive materials used formilitarypurposes.(2) Magnetic imprinted surface enhanced Raman scattering (MI-SERS) basedultrasensitive detection of ciprofloxacin from a mixed sampleA new method for fast extraction and ultra-sensitive detection of ciprofloxacin basedon magneticimprinted surface-enhanced Raman scattering (MI-SERS) has beendeveloped in this part. This methodis a combination of three techniques, which are amagnetic separation technique, a molecular imprintingtechnique and asurface-enhanced Raman scattering technique. We designed and fabricatedcore–shellstructured magnetic molecularly imprinted polymers (MIPs) which can be applied to specificallyrecognise ciprofloxacin and extract it from a mixed system. Thewhole extraction and clean-upprocedures are assisted by a magnetic field, whichmakes it much easier than traditional centrifugalseparation. In addition to this,surface-enhanced Raman scattering (SERS) was applied as the detectiontool, whichmakes the detection limit for ciprofloxacin by this method as low as10-9molL-1.Furthermore, we integrated these core–shelled magnetic-MIPs on a magnet chipand detectedciprofloxacin from fetal bovine serum. The whole detection process canbe finished within ten minutesand the limit of detection by this chip can reach10-7mol L-1.(3) One-Step Detection of Melamine in Milk by Hollow Gold Chip Based onSurface-enhanced Raman ScatteringA hollow gold (HG) chip with high surface-enhanced Raman scattering (SERS)capability was fabricated and used to monitor the adulteration of milk with melamine.This chip was fabricated with self-assembled hollow gold nanospheres (HGNs) onglass wafers through electrostatic interaction. There are two important advantages forthe use of this HG chip as a detection platform. First, HGNs show a strong SERSenhancement from individual particles due to their capability to localize theelectromagnetic fields around the pinholes in hollow shells. Second, the HG chipimproves the limit of detection through the enrichment effect. The characteristicSERS peak of melamine was used to distinguish it from other kinds of proteins oramino acids, and its intensity was used to monitor the percentage of melamine in milk.With its simple detection procedure (no pretreatment or separation steps), decreasedprocessing time and low detection limit, this HG chip shows a strong potential forbroad applications in melamine detection from real samples. |
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