Surface-enhanced Raman Scattering Spectroscopic Studies Of Several Organic/bio-molecules In The Presence Of SnCl₂

Surface-enhanced Raman scattering(SERS)spectroscopy has become an ultrasensitive analytical tool in the fields of surface science, analytical science and biology.Oxidation and decomposition are inherent problems frequently encountered in the SERS measurements,especially for the reactive organic/bio-molecules.Several physical ways for reducing the interference have been reported in the literature,like vacuum, inert atmosphere,low temperature,low laser power,and so on.However, these conditions cannot be met conveniently for routine analysis of SERS. Apparently,development of new chemical methods more operable are required for the effective elimination of oxidation and decomposition of analytes.In this thesis,we have advanced a new convenient chemical way to improve the SERS analysis of some organic/bio-molecules,like pyridoxine(PN),cystine(Cys)and carnosine(Car),by introducing SnCl₂ into the system and disclosed its possible function mechanism.The method has been applied to SERS studies of above molecules on the substrates of coin metals:gold,copper and silver.The main contents of this thesis are summarized as follows:1.The electrochemical behavior and SERS spectra of SnCl₂ have been studied to reveal its effect on improving the SERS measuermnets of reactive biomolecules.The good reductive,adsorptive and coordinative properties of Sn(â…¡)account for the repression of the oxidation and decomposition of biomecules.Firstly,pyridine was employed as a probe molecule to confirm the effect of SnCl₂ on reducing the oxidation and photodegradation.We found that the strongly adsorbed SnCl₂ changed the adsorption mode of pyridine and eliminated the "first layer" effect on pyridine,which is the critical point to avoid the oxidation and photodegradation of pyridine molecule.The negative shift of potential is benefit for the interaction between SnCl₂ and pyridine.2.The SERS study of PN is seriously restricted by its oxidation and decomposition.Fortunately,the introduction of SnCl₂ successfully resolves the above problems and results in high-quality SERS spectra of PN.In this case,Sn(â…¡)strongly coordinates with PN and presents perfect enhanced Raman signals for PN,which is an unusual result in SERS study for biomolecules.Chemical enhancement plays the key role here besides electromagnetic enhancement.The attractive finding provides another novel way to obtain the SERS signals of molecules on roughed substrates by coordination.The application of Sn(â…¡)can be also extended to the substrates of Ag and Cu.3.The presence of SnCl₂ in the mixed solution of PN + Cys can not only avoid the sample decomposition but also be of help for the selective determination of PN or Cys molecules.On the roughened Au electrode, Cys does not interfere the signals of PN for Sn(â…¡)strongly interacts with the Au substrate and PN simultaneously.However,on the roughened Cu electrode,the signals of Cys emerge first as the potential shifts negatively,and then PN starts coadsorbing through Sn(â…¡).This phenomenon is due to the relatively weak affinity of Sn(â…¡)for the roughened Cu substrate.4.Its coordination with Sn(â…¡)can also reduce the oxidation and decomposition of Car so that we are able to resolve the SERS analysis of Car.More types of molecules have been investigated by SERS technique to understand their interaction with Sn(â…¡).