Investigation And Application Of SERS Based On The Silver Nanorods

The Raman spectroscopy,a non-elastic scattering,was related to the molecular rotate and vibrate.Raman spectroscopy has been widely used for identifying the conformation of target molecular,while its weakness also delimited the practical application.The enhanced Raman signal can be observed when target moleculars were attracted to the rough metal surface,such as the noble metal（Ag or Au）surface.The enhancement has reached by roughly 3-7 orders of magnitude.This is surface enhanced Raman spectroscopy（SERS）.The appearance of SERS overcomes the barrier of the low intensity and is unaffected by solvent peak of H2 O.In recent years,because of its advantages such as fast analysis and high-sensitivity,SERS is widely used in medicine,biological molecules,environmental pollution,material science and other fields.In this work,we discussed the obvious enhancement effect of silver nanorods substrate on SERS signal.This substrate is highly sensitive,stable and reproducible.First,we discussed the characteristic of the berberine and compared the SERS substrate only on the silver nanorods with it wrapped BSA.Then,the changes of SERS signal can be ascribed to the interaction of L-cysteine and metal ions.Finally,the adsorption of L-cysteine tagged molecule on the silver nanorodes to detect the mercury ions was tested.It was debated that the specificity of L-cysteine to mercury ions.At the optimum condition,the concentration of mercury ions was determined successfully.Therefore,a simple and fast method was established for determination of mercury.The research methods are as follows:The first chapter mainly introduced the principles,characteristics,the discovered history of Raman spectroscopy and surface enhanced Raman spectroscopy（SERS）.This part introduced the SERS active substrate,recent development and application aboutthis field.This essay also concerned the development direction henceforth of Raman spectroscopy.The second chapter was discussed that silver nanoparticles with different morphology were synthetized by three different methods.These structures were characterized by UV-vis spectroscopy and transmission electron microscopy（SEM）.The Rhodamine B showed different Raman enhanced effect on the three different silver nanoparticles.It was found that silver nanorods had the most obvious enhanced effect.The infrared spectroscopy（IR）spectra and Raman spectra were used to explore the possible mechanism.Experiments show that the Rhodamine B possessed good characteristic vibration bands with concentration at 1×10-7 mol/L,meanwhile,characteristic peaks were most obvious effect and highly reproducible with concentration at 1×10-3 mol/L.Finally,the silver nanorods were chosen to further work.In the third chapter,the Raman spectroscopy and the SERS of the berberine were reported,and the vibrational peaks were assigned.SERS and Raman spectra of solids of the berberine were compared.The results showed that the positions of characteristic peaks were not changed,but strengthen of peaks were enhanced relatively.The study of the SERS spectra of berberine with silver nanorods and it’s with bovine serum albumin（BSA）-coated silver nanowires（Ag@BSA）were analyzed the influence on their systems.Enhanced Raman spectra showed that silver nanorods were linked to N atom of amino acid,O atom of methoxyl,electron of benzene ring and N atom of isoquinoline.Compared the SERS substrate only on the silver nanorods and on the Ag@BSA,it displayed that the SERS on the Ag@BSA was lower,but it was with highly stabilization,which provided important information for further study.In the fourth chapter,Raman spectroscopy and the SERS of L-cysteine on the silver nanorodes were analyzed.The results showed that strengthen of peaks were enhanced relatively.The vibrational and enhanced peaks were assigned.The solid Raman spectra demonstrated the S-H stretching vibration absorption,but could not be found in SERS.This phenomenon proves the chemisorption of the L-cysteine on the silver nanorods surface via the formation of S-Ag bonds.The vibrations of ν（C-O）andν（C-N）was enhanced obviously.At the different pH value,all the different shifts were showed and adsorption behaviors were changed.Under the condition of pH 7 value,vibrations of ν（Ag-S）were constituted meanwhile had the stable vibrations of ν（C-O）and ν（C-N）,Thus,the PH of 7 was selected in this system.In the systems containing different metal salts including Na+,Mg²⁺,Cu²⁺,et al,it was found that the molecularstructure of the L-cysteine was changed under adding metal salts with Al³⁺、Cu²⁺、Zn²⁺、Cd²⁺ and Hg²⁺.The study result showed that the carboxyl groups and metal ions were linked by bonding.At the some time,owing to its vacant d atom orbit,metal ions concluding Cu²⁺、Zn²⁺、Cd²⁺ and Hg²⁺ were able to accept accept single electron pair from sulfur atoms.The Al³⁺ came into precipitation with carboxyl groups easily,so the SERS was the weakest to low resolution.The structure of L-cysteine to join the mercury ion was destroyed completely.Though alternating the condition of pH value,proportion and concentration,the SERS of complexes of metal ions with L-cysteine was changed.The results showed that strengthen of peaks decreased as the pH value,proportion and concentration increased.Provide important information for the protein denaturation and heavy metal pollution.In the final part,a detection of trace Hg（Ⅱ）was based on silver nanorods by SERS activity.We discussed the probe types and concluded that the L-cysteine with a high selectivity and sensitivity for Hg（Ⅱ）.The UV-vis spectroscopy was conducted in order to proves the uniformity and dispersity of silver nanorods and it can be modified L-cysteine.Based on L-cysteine of SERS was high sensitivity and selectivity for Hg（Ⅱ）on condition that the ten kinds of metal ions carried on,but only when the single-peak at1040 cm-1 structure appears after adding the Hg（Ⅱ）.SERS sensor with L-cysteine assembled silver nanorods firmly captured the Hg（Ⅱ）through the carboxyl groups.The effect of the concentration and pH on the probe was also investigated.1×10-3 mol/L L-cysteine and the pH of 7 was selected in this work.It does not have a great effect on temperatures,but was down trend over 55℃.In order to protect the structure of L-cysteine and form complexes rapidly,45℃ was chosen as the optimal for further experiments.Under the optimized conditions,a series of the concentration of mercury ions were measured,which the result showed that the density of mercury ions ranging from 1×10-8 mol/L to 1×10-6 mol/L can be analyzed due to a strong peak at 1040 cm-1with good linear relationships（correlation=0.988）.Desirable recoveries within the range of 85-103 % were obtained,showing that this method has excellent sensitivity and stability for detection of trace Hg in real water samples.