Construction Of Plasmonic Metal Heterostructures And Their Surface-Enhanced Raman Properties

Plasmonic metal could generate significant localized surface plasmon resonance（LSPR）effect under the excitation of incident light,thereby inducing the formation of strong localized electromagnetic field,and the Raman signal intensity of the probe molecules attached to its surface can be greatly improved.Therefore,it can be used as an excellent surface-enhanced Raman scattering（SERS）substrate,which has broad application prospects in environmental monitoring,food safety,biomedicine and other fields.In particular,plasmonic metal heterostructures have synergistic coupling effect between different components and exhibit significantly enhanced SERS activity in comparison with single metal.Metal/semiconductor heterostructures formed by the combination of plasmonic metal and semiconductor nanomaterial possess the physical enhancement produced by plasmonic metal and the chemical enhancement caused by semiconductor nanomaterial.Moreover,the synergistic effect at the heterointerface can significantly improve the electron transport efficiency,and further improve the SERS activity.Therefore,continuous regulation and optimization of the microscopic configuration of plasmonic metal/semiconductor heterostructures can provide new opportunities for ultrasensitive chemical and biological sensing,which is of great significance to the research of SERS frontier field.Over the years,researchers have made a series of achievements in regulating and designing the microscopic configuration of plasmonic metal heterostructures.However,in order to realize the regulation of polymorphic heterostructures,conventional synthetic methods require the use of complex macromolecular organic reagents as stabilizers/capping agents/heterostructure-directed growth additives.The organic reagents remaining on the surface of the material require additional cleaning-purification processes to remove them.In recent years,laser-induced photochemical strategy,as a green synthesis method,does not require additional organic auxiliary reagents,which provides a new idea for the controllable synthesis of plasmonic metal/semiconductor heterostructures with clean surfaces.In addition,the easily tunable laser parameters are beneficial to realize the optimal design of polymorphic heterostructures,which further promotes the in-depth study of ultra-sensitive molecular diagnosis.In this thesis,the microstructures of plasmonic metal heterostructures have been regulated and optimized by laser-induced photochemical synthesis strategy.Bimetallic AuAg nanochains,TiO₂ nanowires-supported Au@Ag nanodendrites,TiO₂ nanorod arrays（NRAs）-supported Au/Ag nanoparticles（NPs）,and Cu₂O octahedrons-supported vine-like Ag nanostructures four highly active SERS substrates have been successfully constructed and a series of SERS application studies have been carried out.In addition,we have performed meaningful extended research work to further explore the catalytic activity of plasmonic metal/semiconductor heterostructures as peroxidase-like enzymes.The main research contents of this thesis are as follows:1.Controllable preparation of bimetallic AuAg nanochains to explore the excellent SERS performance based on the synergistic effect of the bimetallic interface.Firstly,Au nanotwins with abundant-OH on the surface were prepared by laser liquid phase ablation strategy,then-OH was used as unique reducing agent to realize the subsequent efficient reduction of Ag+.Compared with conventional synthesis methods,this strategy does not need to add additional auxiliary and reducing reagents,ensuring that the surface of the synthesized materials is clean and free of contamination,which is beneficial to the trace detection of target molecules.The experimental results show that the Raman signal intensity of AuAg nanochains with CV as the probe molecules can reach 4.5 times that of Au nanotwins,and the detection limit of CV molecules is as low as nanomolar level（nM,10-9 M）.Compared with Au nanotwins,the synergistic effect of Au and Ag in bimetallic nanochains is beneficial to the transmission of photoexcited electrons,which plays an important role in the improvement of SERS activity.The substrate materials can be actually applied to sensitive SERS detection of organic pesticide residues thiram,tricyclazole and benzimidazole on apple surfaces,which provides a basis for the quantitative analysis of pesticide residues in agricultural products.2.Controllable design of Au@Ag nanodendrites/TiO₂ nanowires to explore the enhanced SERS performance of plasmonic metal/semiconductor heterostructures under the excitation of blue light（473 nm）.AgNPs were deposited on TiO₂ nanowires by UV light（375 nm）liquid phase-induced photochemical synthesis strategy,and then Au@Ag nanodendrites modified TiO₂ nanocomposites were constructed by direct reduction method.The results show that the Raman intensity of CV molecules in this nanocomposite configuration is 5.6 times that of Au@Ag nanodendrites.The significantly enhanced SERS activity is not only related to the electromagnetic enhancement produced by Au@Ag nanodendrites and the chemical enhancement generated by blue light excited TiO₂,but also the electron transport at the heterointerface plays an additional contribution to the improvement of SERS activity.Accordingly,the pH sensing properties of plasmonic metal/semiconductor heterostructures under blue light excitation were explored by using 4-mercaptobenzoic acid（4-MBA）as the pH indicator molecule.The research shows that Au@Ag/TiO₂ not only exhibits good linear response to pH changes in complex environments,but also provides excellent temperature and time stabilities for pH sensing,which is very important for sensitive detection of pH in practical biological environments.This study proposes an effective SERS-based pH sensing strategy by using short-wavelength laser as the excitation light source,it can effectively overcome the thermal effect generated from visible or near-infrared（NIR）light,providing an alternative solution for pH detection of some photothermal sensitive molecules.3.Based on the above-mentioned laser liquid phase-induced synthesis strategy,dense Au/AgNPs were loaded on TiO₂ NRAs to explore the enhanced NIR-SERS performance of the heterostructures.Due to the synergistic effect between the bimetals,the nanocomposite configuration exhibits significantly enhanced absorption capacity in the range of 400-1300 nm compared to the loading of Au or AgNPs.It can be found that Au/AgNPs-TiO₂ NRAs has significantly improved SERS activity by using CV as the probe molecules,which is 7.2 and 2.9 times that of AuNPs-TiO₂ NRAs and AgNPs-TiO₂ NRAs,respectively.The improvement of SERS activity is attributed to the significantly enhanced synergistic coupling effect at the heterointerface of the ternary system.Accordingly,we applied it to the trace detection of antibiotics ciprofloxacin and chloramphenicol in real water environment with detection limits up to 10-9M and 10-8M,respectively.Moreover,the efficient SERS recycling applications are realized by utilizing the excellent photocatalytic degradation ability of plasmonic metal/semiconductor heterostructures.The SERS research carried out by NIR light excitation can effectively reduce the fluorescence noise signal,and has stronger penetrating ability of biological tissues in comparison with UV and visible light excitation,which is conducive to the subsequent application research in the field of biomedicine.4.Based on the laser liquid phase-induced photochemical synthesis strategy,vine-like Ag nanostructures were deposited on Cu₂O octahedrons,and their excellent SERS performance in complex systems was explored.Compared with Cu₂O modified by monodispersed AgNPs,the constructed Ag nano vines（NVs）/Cu₂O octahedrons heterostructures exhibit significantly improved SERS activity,which is 2.7 times that of AgNPs/Cu₂O heterostructures,and the detection limit for CV molecules is as low as 10-14 M.The enhanced SERS activity is attributed to the efficient heterointerface electron transport efficiency provided by this unique heterostructures,which could not only enhance the chemical enhancement,but also improve the physical enhancement effect.Based on this,we have realized the microdetection of the pesticide residues thiram in soil and urine samples,and the detection limit could reach 0.48 ng g-1 and 10-7 M,respectively.Compared with loading AgNPs in conventional studies,this vine-like Ag nanostructures-connected heterostructures exhibit significantly enhanced SERS activity,which opens up a new idea for the construction of highly active SERS substrates.5.On the basis of the previous research work,we carried out meaningful extended study on the synthesis of AuNPs/Cu₂O cube heterostructures,and explored the peroxidase-like catalytic activity.In the presence of H2O₂,Au/Cu₂O heterostructures exhibit higher catalytic activity for the oxidation of TMB in comparison with single Au and Cu₂O,which is mainly attributed to the efficient electron transfer between Au and Cu₂O.Based on the excellent catalytic activity of the heterostructures,it can be applied to the sensitive detection of H2O₂,and evaluation the antioxidant capacity and detection of three antioxidants.The research work has broad application prospects in the fields of biomedicine and food safety.