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Synthesis Of New Nano-silver Substrate And Surface-enhanced Raman Spectroscopy Analysis Of Shewanella Bacteria

Posted on:2015-02-14Degree:MasterType:Thesis
Country:ChinaCandidate:A X ChenFull Text:PDF
GTID:2251330428497403Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
Due to the introduction of active substrates, the technique of surface enhanced Raman spectroscopy (SERS) can overcome the disadvantages of low sensitivity and strong fluorescence interference of the technique of normal Raman spectroscopy. The technique of SERS has been widely applied in many fields including surface science, analytical science and biological science. The fabrication of high stable and reproducible active substrates with lots of controllable "hot" spots by nanostructured synthesis techniques is one major research of SERS. Research of the SERS active substrate can not only promote the further study of SERS mechanism, but also can further enlarge the application fields of SERS.Compared with the other analytical techniques of microorganism, SERS has the advantages of non-contact, non-destruction, simple sample preparing, less sample amount, high sensitivity and repeatability. The rapid and nondestructive analysis of microorganisms can be implemented by SERS. More readable Raman peaks can be obtained for microorganism with the use of a wide range of excitation wavelength. The SERS technique has been widely applied to study the microbial cell composition and metabolic process. It is one of the important techniques for microbial classification, identification and detection,In this paper, the study of new SERS substrate and SERS application in microbiological analysis is outlined as follows:1. Synthesis and application of new nano-silver substrates. Silver nanoparticles was respectively synthetized with water extract of Macaranga tanarius and dissimilatory metal reducing bacteria of Shewanella oneidensis MR-1(MR-1). Copper-silver (Cu-Ag) film was formed by metal replacement reaction on the copper sheets passivated by sulfuric acid-ultrasonic sound or by low temperature. Other types of silver nanoparticles film were prepared by electrostatic adsorption of sodium citrate-reduced colloidal silver nanopaticles on the templates of the cotton make-up powder-puffs and quantitative filter papers. The new nano-silver materials were investigated regarding their suitability as active substrates for SERS analysis of chloramphenicol, acyclovir and MR-1, and were found that:(1) Compared with the sodium citrate-reduced colloidal silver nanopaticles, the technique of sulfuric acid-passivated Cu-Ag film and low temperature-treated Cu-Ag film exhibited higher activity for SERS analysis of acyclovir.Sulfuric acid-passivated Cu-Ag film as substrate had better homogeneity, stability and lower acyclovir detection limit. No significant decreasing of peak intensity was observed with the substrate kept for14days in the room temperature. The lowest detection limit for was acyclovir of1×10-4mol/L.(2) The powder-puff-silver film can enhance the SERS signal response to MR-1. However, about Δ20cm-1Raman shift was observed for the characteristic peaks of MR-1.(3) Though signal intensity of the MR-1Raman peaks was not increased with the dissimilatory metal reduction bacteria-reduced silver particles as a substrate, the obtained unique Raman peaks for MR-1can be used for identification of dissimilatory metal reducing Shewanella bacteria.2. Development of a new SERS method for identification of dissimilatory metal reducing bacteria. Ag (I) can be reduced to Ag (0) by the extracellular electron ransfer capacity (EET) of gram negative anaerobic bacterium Shewanella. The obtained Ag (0) on the bacteria membrane was used as the active substrate for Shewanella SERS analysis. Unique Raman characteristic peaks were obtained for each Shewanella subspecies, Shewanella oneidensis MR-1, decolorization Shewanella, and Shewanella putrefaciens. This method can rapidly and accurately differentiate metal reducing bacteria and non metal reducing bacteria such as Escherichia coli, and identify different metal reducing bacteria. The establishment of the method not only can further promote the application of Shewanella bactera in geochemical cycle, biological corrosion, bioremediation, biological productivity, but also overcame the disadvantage of normal Raman spectroscopy and nano silver sol-based SERS which probably give similar Raman spectrum for different bacteria.3. Establishment of a self-assembled silver nanoparticle mediated SERS method for in situ characterization of Shewanella extracellular polymer substance (EPS). Firstly, poly-L-lysine (PLL)-AgNP stable complexes was formed by the electrostatic attraction between positive-charged PLL and negative charged nano-silver sol synthesized with sodium citrate. Secondly, Negative charged Shewanella MR-1was surrounded with PLL-AgNP complex by electrostatic attraction. By comparison of each SERS spectrum of MR-1-PLL-AgNP complexes, MR-1and EPS, it was found that all peaks from EPS can be observed in the MR-1-PLL-AgNP complexes spectrum, but not observed in the MR-1spectrum which was obtained using nano silver sol as substrate. In addition, this established method can obtain more accurate EPS information than the other spectral methods which only can analyze the extracted EPS.
Keywords/Search Tags:Surface-Enhanced Raman spectroscopy, Active substrate, Microorganisms, Extracellular polymers, Identification
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