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Localized Surface Plasmon Resonance Coupled Surface Enhanced Raman Spectroscopy To Determinate Some Medicinal Molecules

Posted on:2015-03-20Degree:MasterType:Thesis
Country:ChinaCandidate:X LiaoFull Text:PDF
GTID:2251330428998724Subject:Analytical Chemistry
Abstract/Summary:PDF Full Text Request
Gold nanoparticles exhibit well-defined optical properties on account of theirlocalized surface plasmon resonance (LSPR) and surface-enhanced Ramanspectroscopy(SERS). LSPR arises from the resonant oscillation of conductionelectrons on the surface of metal nanoparticles. When the incident light frequency andthe free electron collective oscillation frequency are the same, resonance can beproduced. In aqueous solution, gold nanoparticles exhibit strong plasmon bands thatare depended on their geometric shape, core–shell structure, size and the surroundingmedium conditions. LSPR effect highly related to the dielectric constant. Therefore,the adsorptions of chemical substances or biomolecules to surfaces of metalnano-structures can be detected by measuring the absorption or extinction spectrasince the molecular adsorption gives rise to an increase in the dielectric constant nearthe surface.Although LSPR can be used to monitor the binding of macromolecules tofunctionalized nanoparticle surfaces, extinction spectroscopy does not allow forspecific identification of the chemical entity. SERS is a surface sensitive techniquethat results from the enhancement of Raman scattering by molecules adsorbed onrough metal surface. Individual bands in a SERS spectrum are characteristic of aspecific molecular motion. By combining SERS and LSPR spectroscopy, thedetection and structural identification of molecules can be made.Gold nanostructures, especially, core–shell nanoparticles have been applied tomany fields and received the critical attention because their optical properties depend on the shape and size of the nanostructures. Core–shell nanoparticles own their uniqueplasmonic properties, fascinating optical, electronic, and catalytic properties, whichare different from the individual metallic counterpart because of the combination oftwo kinds of metals and their fine structures, evolving new surface characteristics.On the other hand, nonspherical gold nanostructures received the great attentionbecause their optical properties depend on the shape and size of the nanostructures.Nonspherical gold nanostructures possess two surface-plasmon resonancescorresponding to the electron oscillations along the longitudinal and transversedirections. For example, gold bipyramids and gold nanorods have two distinct surfaceplasmon-resonance bands. Gold bipyramids have a pentagonal base and two sharpapexes. Thus, gold bipyramid substrates have higher refractive index sensitivity and anarrower LSPR line width than gold nanorod substrates.2-mercapto-1-methylimidazole (methimazole) was determined by LSPR andSERS spectrometry in the second chapter. Au–Ag–Au double shell nanoparticleswere prepared based on the reduction of the metal salts HAuCl4and AgNO3at thesurface of seed particles. Due to the synergistic effect between Au and Ag, the hybridnanoparticles are particularly stable and show excellent performances on the detectionof2-mercapto-1-methylimidazole (methimazole). The binding of target molecule atthe surface of Au–Ag–Au double shell nanoparticles was demonstrated based on bothlocalized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering(SERS) spectra. Under the optimal conditions, the ratios of absorbance at twowavelengths are directly proportional to the methimazole concentration in the rangeof0.10-3.00×10-7mol L-1. The experimental results indicated that compared with goldnanospheres, Au–Ag–Au double shell nanoparticles were applied, higher sensitivityand wider linear range for the determination of methimazole were obtained. Theapplication of the proposed method in real samples was investigated, and theexperimental results demonstrated the ability of gold nanoparticles as a new probe fordetermination of methimazole in real samples.Gold bipyramids was used as substrates to determine2-mercaptoethanesulfonate(mesna) by LSPR and SERS spectrometry in the third chapter. The gold bipyramids were synthesized by a seed-mediated method in aqueous cetyltrimethylammoniumbromide (CTAB) solutions. Mesna molecules can be strongly adsorbed on the surfaceof gold bipyramids by–SH and induce the aggregation of gold nanoparticles, whichalters the local refractive index in the vicinity of the nanoparticles and results in ashift of the LSPR spectrum. The LSPR intensity is directly proportional to the mesnaconcentration in the range of0.30-4.00×10-7mol L-1. The SERS spectrum can beapplied in identification of mesna molecule. The LSPR and SERS spectrum can beused to qualitative and quantitative applications. The application of the proposedmethod was detected in real samples, and the experimental results demonstrated theability of gold bipyramids as a new probe for determination of mesna in real samples.
Keywords/Search Tags:Localized surface plasmon resonance (LSPR), Surface-enhanced Ramanspectroscopy (SERS), Au–Ag–Au double shell nanoparticles, Gold bipyramids, methimazole, mesna
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