Fabrication And Application Of High-performance Substrates As Surface-enhanced Raman Scattering Platforms

Surface-enhanced Raman Scattering(SERS)is one of the advanced analytical methods for trace analysis with superiority in sensitivity and easiness in operation.It shows enormous applications in many areas such as trace detection,reaction process monitoring,biological imaging and so on.Design and fabrication of better substrate is the most effective way to promote the analytical performance of SERS based method.Different targets may have distinct Raman response,and their interaction with SERS substrates are often quite different.In this dissertation,we fabricated several kinds of SERS substrate with good enhancing ability and homogeneity based on the property of specific targets,and then established a series of SERS analytical methods by using these substrates.The main contents of the dissertation were shown below.Chapter 1 summarized the basic information of SERS and newest research progress in SERS substrate development.In this chapter,the main goal of this dissertation was introduced.In Chapter 2,magnetic Fe3O4/Ag NPs were fabricated and used for detection of glutathione(GSH).By fixing Ag NPs onto Fe3O4 NPs,uncontrollable aggregation of the Ag NPs was prevented,which ensured the signal reproducibility.Moreover,the magnetic particles could be further assembled to produce more hot spots.Since GSH is Raman inactive,Raman active crystal violet(CV)was used as probe.The interaction between Ag NPs and S in GSH is stronger than that between Ag and N in CV,and hence GSH can replace absorbed CV on Ag surface.The intensity decrease of CV showed linear responses to GSH concentration in the range of 50-700 nmol L-1.The limit of detection(LOD)was low to 40 nmol L-1.This method showed good selectivity without interference from common co-exist ions and small molecules.In Chapter 3,a graphene wrapped Ag array substrate was fabricated by laser wrapping graphene layer onto the pre-self-assembled Ag array,and then the new substrate was used for the detection of trace methylation-related DNA.The assembled Ag array promoted the homogeneity of the substrate and also contributed to the generation of dense hot spots.Two dimensional graphene functioned as protector to prevent the metal nanoparticles from oxidation and as a barrier isolating the Ag particles from direct contacting the analytes.Our experimental and simulation results proved the effective electromagnetic coupling between graphene and the Ag array.The obtained substrate was applied to detect trace methylated DNA(5mC)and its two oxidized derivatives with the help of antibody modified Au NPs as capture scaffold.The LOD for 5 mCwas as low as 1.8 pmol L"1.In Chapters 4 and 5,three dimensional hydorgel substrates were fabricated by in situ reduction and frozen-gelling strategy on the basis of polyvinyl alcohol(PVA)hydrogel,and used for detection of trace organic pollutants.The obtained hydrogel substrate showed excellent homogeneity in the range of its bulky volume.Depth scanning and slice experiments proved that its efficient penetration depth for the SERS analysis was more than 100 ?m,which greatly promoted the enhancing effect.To further improve its ability of detecting hydrophobic targets,?-cyclodextrin(CD)was used as functional molecule to modify the surface of Ag NPs.By using the surface modefied Ag NPs,a PVA-CD-Ag hydrogel substrate was prepared.Owing to the specific host-guest interaction between CD and targets,the modified substrate was successfully applied for the detection of trace antibiotics(three sulfanilamides and three quinolones)with LOD as low as 5 ng mL-1.In Chapter 6,a SERS active emulsion based platform was fabricated for the multiple phase interfacial reaction monitoring.CD was used as both emulsifier and modifier to assembling Ag NPs into plasmonic emulsions.Ag NPs were closely packed on the surface of the emulsion,which produced many hot spots,and these particles had access to two phases simultaneously which could be used for interfacial reaction monitoring.Based on this new substrate,we monitored two typical reactions,the reaction of o-phenylenediamine(OPD)with NO2-,and the light catalytic OPD oxidation.From the SERS monitoring,the reaction kinetics were obtained.Chapter 7 summarized the conclusions obtained in the present dissertation and gave a prospect of further researches about SERS substrate development.