Preparation And Surface-enhanced Raman Scattering Effect Of Graphene Oxide/(Au/Ag) Hybrid Materials

Surface enhanced Raman scattering(SERS)is an ultrasensitive technique for chemical sensing,pollutant detection,bioimaging and cancer diagnosis.Nowdays,preparation of SERS substrates with high SERS effect,good uniformity and stability and in-deep study of the SERS mechanism have been a major challenge for researchers.Ag and Au are the most widely used metals for SERS applications because their surface plasmons can be excited with most of the visible lasers used in Raman spectroscopy.Graphene oxide play an important role in chemical enhancement,molecule enrichment,surface passivation and fluorescence quencher.It has a vital significance for preparation of graphene oxide /(Au/Ag)hybtid materials combining with the respective advantages of the Au/Ag nanoparticles and graphene oxide.In this paper,graphene oxide /(Au/Ag)hybtid materials with excellent SERS effect have been prepared.The important and valuable results are summarized as follows:(1)A novel class of hierarchically silver particles were facilely synthesized by solution reducing process with different organic acids(oxalic acid,DL-malic acid and citric acid)as structure-directing reagents.The anisotropic morphologies of as-synthesized silver structures were tunable by varying different structures of organic acids,the concentrations of reagents and the growth temperature under otherwise identical conditions.The chemical nature of organic acids with different number of carboxyl groups were proved to be critical in assembly manner of metal nanoparticles into hierarchical complex structures.Silver ions can be combined with the carboxyl groups,affecting the self-assembly process of silver particles.The Ag particles synthesized with citric acid have the most abundant hot spots and exhibit an excellent surface enhanced Raman scattering(SERS)effect.The limit of detection of R6 G could be 10-14 M,the enhancement factor could be achieved to 4.12×106.(2)Gold nanostars(Au Nst)were synthesized by seed-mediated growth method with Ag nanoparticles as seeds,ascorbic acid as reducdants and chloroauric acid as precursors.The anisotropic morphologies of gold nanostars were tunable by varying the concentrations of AgNO3,HAuCl4 and the addition of halogen ions.AuNst/GO/AuNst sandwich structures were synthesized by spin-coating and filtration methods.The excellent SERS effect of AuNst/GO/AuNst sandwich structures are based on the multi-dimensional coupling between the gold nanostars and the chemical enhancement,molecule enrichment and surface passivation from GO.The limit detection of R6 G could be 10-13 M,the enhancement factor could be achieved to 6.64×108.The variations of relative Raman intensity 20 random sites were less than 6 %,suggesting the extremely high uniformity of AuNst/GO/AuNst substrates.(3)Ag@GO@Au substrates were synthesized using cysteamine and 2-mercaptopyridine as modificatory reagent.The excellent SERS effect of Ag@GO@Au substrates are based on the multi-dimensional coupling between the Ag particles and gold nanoparticles and the chemical enhancement,molecule enrichment and surface passivation from GO.The limit detection of R6 G could be 10-13 M,the enhancement factor could be achieve to 2.93×107.The variations of relative Raman intensity 20 random sites were less than 7 %,suggesting the extremely high uniformity of Ag@GO@Au substrates.After exposure to ambient environment for 30 days,the signal intensities on Ag@GO@Au hybrid structures were descend to 88 %,suggesting the high stability of Ag@GO@Au substrates.(4)Ag/GO/AuNst sandwich structure was synthesized by chemical modification and spincoating methods.The excellent SERS effect of Ag/GO/AuNst substrates are based on the multidimensional coupling between the Ag particles and gold nanostars and the chemical enhancement,molecule enrichment and surface passivation from GO.The limit detection of R6 G could be 10-14 M,the enhancement factor could be achieved to 7.51×108.The variations of relative Raman intensity 20 random sites were less than 7 %,suggesting the extremely high uniformity of Ag/GO/Au Nst substrates.After exposure to ambient environment for 30 days,the signal intensities on Ag/GO/AuNst substrates were descend to 89 %,suggesting the high stability of Ag/GO/AuNst substrates.