Construction Of Ionic Liquid-based SERS Substrate Via Co-assembly And Its Applied Research

Surface Enhanced Raman Scattering?SERS?effectively solved the low sensitivity and poor selectivity of conventional Raman detection in structure analysis.Immediately attracted the attention of researchers once it was found.After decades of intensive research,great progress has been made in understanding the SERS effect.The research of hotspots mainly focused on the enhancement mechanism,construction of the SERS substrates and the application of SERS technology.Based on the excellent performance of ionic liquid-based functional materials and the new-type integrated strategy,this thesis is intended to the construction of new SERS substrates and their ultrasensitive SERS detection.The second chapter focused on the construction of novel SERS substrate and its structure stability.Combining the reactivity of ionic liquids?ILs?and the isotropic structure of liposomes,a new-type substrate of IL-based liposome-Au with high stability and sensitivity has been established.In order to overcome the structural instability of liposome,through thermal initiated polymerization of C=C bonds,the unique isotropic structure and vesicular shape could be freezed efficiently.The achieving liposome with remarkable structure stability laid the foundation for the loading of Au nanoparticles?NPs?and Raman reporters.Based on the coordination effect of ILs on metal NPs,Au NPs could be uniformly and stably grown on the substrate surface.The electromagnetic coupling between particles was favorable for the formation of hotspots.In addition,the isotropic liposome promoted inorganic Au NPs uniformly modified on the substrate,which was beneficial for the generation of large-scale hotspots that covered the whole surface.Besides,the effects of loaded Au NPs on reactivity of IL-segments were systematically explored.The results showed that the decoration of Au NPs did not affect the reactivity.At the same time,this Au NPs assembly was preserved intact during the reaction,indicating the coordination of IL on Au NPs has sufficient strength,which was conducive to the modification of Raman probes.On this basis,the SERS performance of liposome-Au for methyl orange?MO?was investigated.Results showed that the Raman signals of MO were significant enhanced on this substrate,thereby exhibiting the potential application in SERS detection.In chapter 3,the ternary SERS platform of liposome-Au/probes was established via the strategy of co-assembly and its application performance in SERS detection was systematically investigated.This innovative detection mode,different from the conventional thiol-linked SERS systems,has the following three advantages.First,the co-assembly broke the shackles of traditional SERS analysis relying on sulfhydryl combination,and expedited SERS development in detecting molecules with no specific affinity to plasmonic surfaces.Second,the isotropic surface of liposome provides the advantage for the evenly and densely growth of Au NPs.This piling up caused the coupling of local electromagnetic fields,which further promoting the formation of large-scaled hotspots.It was important for the obtention of repeatable and stable SERS signals.Third,thanks to the directional induction of IL units,the selective enrichment and location of anionic Raman probes in the hot regions was realized.This cooperation of hotspots-motivated and hot region-located SERS detection achieving high selectivity and sensitivity for anionic probes.In addition,the anion-exchange of liposome-Au also endowed it with excellent properties such as universality,charge selectivity and solid-phase micro-extraction?SPME?.In the fourth chapter,further explored the construction of SERS substrate and its Raman application.Based on the specific?-?binding between polymerized ionic liquid?poly[ViEtIm]Br?and graphene oxide?GO?,the nanocomposites of rGO-Poly[ViEt Im]Br was prepared.Both of the coordination effect of poly[ViEtIm]Br toward metal NPs and its ion-exchange reaction enabled the two components of organic probes and inorganic Au NPs to achieve co-assembly.As a result,a ultrasensitive SERS detection system of“rGO-Poly[ViEtIm]-Au/probes”was finally set up.This integrated SERS detection system has several advantages.First,the modification of Poly[ViEtIm]Br blocked the conjugated aromatic structure of the substrate,and purified the high selectivity of electrostatic adsorption based on Poly[ViEtIm]Br.Besides,this modification endowed the substrate with excellent reactivity and selectivity,which is conducive to the recognition and detection of specific anions in complex systems.Second,benefiting from the modification of polar Poly[ViEtIm]Br,Au NPs could densely growth on the substrate to form hotspots at microscopic level,while the rGO-Poly[ViEt Im]Br still maintained a better dispersed state at macroscopic level.Second,the anion-exchange equipped rGO-Poly[ViEt Im]-Au with high sensitivity,universality and charge selectivity for the detection of anionic probes.In addition,the huge specific surface of the opened GO endowed this SERS substrate with excellent solid-phase microextraction?SPME?.It was beneficial to the trace detection and the construction of the hotspots-motivated SERS detection mode.Based on this,the limit of detection?LOD?of rGO-Poly[ViEt Im]-Au for methyl blue?MB?was reduced to 10^-14 M.In the fifth chapter,the potential application of rGO-Poly[ViEt Im]Br in SERS detection and other field of catalysis were further explored.As the key factor that greatly restricts the development of SERS technology,the SERS substrate with repeatability and stability have been served as the basis to obtain high-quality SERS signal.Based on the integration of two different components,such as the organic component of Poly[Vi Et Im]Br with excellent properties of co-assembly,reversible ion-exchange and selective adsorption,and the inorganic component of rGO with large surface area and two dimensional open structure,an reusable SERS substrate with excellent sensitivity was designed.Based on this specific substrate,a novel SERS analysis method named“solid phase extraction-SERS detection-substrate renewal”was further established.This novel SERS substrate can be synthesized via a step-wised process.Briefly,Poly[ViEtIm]Br was firstly assembled onto r GO through?-?interaction.Due to the ion-exchange reaction and the followed in-situ reduction,Au NPs can be subsequently grown onto the surface of graphene.Benefiting from the reaction of the modified Poly[ViEt Im]Br,anionic organic probes can be enriched and anchored onto the formed SERS substrate.It is interesting that the modified anionic probes can also be erased by excessive halogen ions to realize the renewal of SERS substrate owing to the reversibility of ion-exchange reaction.Afterwards,the second type of anionic probe can then be rewritten onto the updated substrate via another cycle of ion-exchange reaction,resulting in the flexible formation of novel SERS system.Therefore,the construction of disc-like SERS substrate with erasable function can realize the high selective and sensitive detection toward different probes on the same substrate.It was worth noting that the information stored on the substrate was changed during the erasable process,while the storage performance kept remaining.In addition,this updated substrate still has an excellent erasable ability after five cycles.This kind of disc-like storage performance effectively provided new ideas for the construction of SERS detection system,and showed the potential application in the field of functional materials.