Construction And Application Of PH SERS Probes Based On Au@Ag@Au NCs

Noble metal nanomaterials have been widely used in the study of surface-enhanced Raman scattering(SERS)spectroscopy due to their remarkable local surface plasmon resonance effect.Because of its advantages of high sensitivity,no fluorescence interference and non-destructibility,SERS spectroscopy technology has been widely used in sensor detection,biochemical analysis,biological imaging and other fields.The SERS response of molecules on noble metal Raman substrate is closely related to the size distribution,geometric morphology,assembly structure and chemical composition of noble metal.Therefore,research workers prepared the nanoparticles with special structure and the substrate structure with excellent performance used for SERS probe building,such as the exploring synthesis methods of precious metal nanoparticles with different morphology and chemical composition and the dimers or array structure substrate preparation methods,so that the SERS probe can achieve rapid,stable and reliable detection.As we all know,pH value detection is of great significance in both environmental detection and biochemical analysis.This paper mainly explored a synthesis method of gold coated gold core silver shell cubic nanoparticles(Au@Ag@Au NCs),and constructed two SERS probes based on it which can be used in detection of pH value of environmental water.Based on gold core silver shell cubic nanoparticles(Au@Ag NCs),a gold layer was coated on Au@Ag NCs by improved in-situ reduction deposition method whose purpose is to alleviate the oxidation problem of silver layer on Au@Ag NCs.Then,using Au@Ag@Au NCs as the substrate,two SERS probes were constructed to detect the pH value of water through the interaction of sulfhydryl group and heterocyclic sulfur with gold in Raman report molecules.In the acid and alkaline environment,the pyridine or amino structure in reporter molecular structure can occur a series of proton and proton process,which can result in the molecular structure change.This kind of change will cause SERS signals corresponding changes,which can achieve rapid and sensitive detection of environmental water pH value.In addition,the reversible change of the reporter molecule structure in acid-base environment can be used to detect pH circularly.Firstly,the gold spheres with uniform morphology and controllable size were prepared by seed growth method as the core,and then Au@Ag NCs was obtained by wrapping silver on the surface of the gold spheres through reduction deposition.Then,by regulating the amount of Na OH and chlorauric,a thin layer of gold shell was coated on the surface of Au@Ag NCs,so as to successfully prepare monodisperse Au@Ag@Au NCs,which was characterized by Uv-visible(UV-vis)absorption spectrum,dark field microscope(DMF)and Transmission electron microscope(TEM),respectively.The results showed that Au@Ag@Au NCs had better oxidation resistance and cubic morphology than Au@Ag NCs.Secondly,the interaction between heterocyclic sulfur and gold was used to modify 5-(4-pyridine-2-thiazolide)on Au@Ag@Ag NCs,and then inducer was added to promote the aggregation of Au@Ag@Ag NCs.A pH SERS probe was constructed by means of the nanoparticles aggregation leading to SERS signal enhancement.The SERS spectrometer was used to investigate the spectral changes and cyclic stability of Au@Ag@Ag NCs5-(4-pyridine-2-thiazolamide)probe in B-R buffer and its application in pH detection of river water.Finally,an evaporative self-assembly method was adopted to adsorb a layer Au@Ag@Au NCs on the glass plate modified with sulfhydryl group to prepare a kind of SERS substrate,which has more uniform and reliable SERS signal compared with Au@Ag@Au NCs aggregate.Subsequently,4-aminobenzyl mercaptan(4-ATP)Raman reporter molecules were modified on SERS substrate by the interaction between sulfhydryl group and gold.The amino group in 4-aminobenzylmercaptan can protonate with hydrogen ions in the solution under acidic conditions,and form nitrogennitrogen double bond structure with adjacent molecules under alkaline conditions.Moreover,the structural change process of 4-ATP in acid-base environment is reversible,which can be intuitively shown from SERS spectrum.Based on this,we developed a nano-pH probe based on SERS spectroscopy technology of microregion that can be used for cyclic detection of pH value.