The Controlled Preparation Of Two-Dimensional Nanostructures Based On Polymer Brushes And Their Surface-Enhanced Raman Scattering(SERS)

Since the discovery of the phenomenon of surface-enhanced Raman scattering（SERS）,it has gradually become an important tool for the analysis of material compositions and structures.The applications of SERS have been expanded from the fields of environmental and materials science to biomedicine,due to the extremely high sensitivity and non-destructiveness of SERS-based analytical technology that even allows single molecule detection.During the past few decades,the explosive development of nanomaterials and nanotechnology has further promoted the study of SERS technology,as novel nanomaterial-based SERS substrates exhibited enhanced detection performance.To date,it has been widely accepted that the morphology,size,composition,and stacking of nanomaterials have huge impacts on the strength of the SERS effect.However,for traditional wet synthesis of nanomaterials,precise control over these parameters is still a challenge.Therefore,it is necessary to develop an alternative nanofabrication technology to prepare nanostructures with precise and controllable shape,adjustable chemical composition,independently controllable horizontal size and vertical thickness,and customizable patterns.In this Dissertation,we first aimed to develop a general and robust template synthesis method to prepare patterned assemblies of inorganic nanoparticles into arbitrary patterns with tunable dimensions.Using this method,we prepared patterned gold（Au）nanoparticle assemblies on a silicon wafer and investigated its SERS effect.Our results suggested that such Au nanoparticle assemblies were highly sensitive and reliable SERS substrates.Moreover,we further demonstrated a flexible SERS substrate and expanded the application of our template synthesis method to prepare assembled core-shell type nanoparticles.The major contents and conclusions of this Dissertation are briefed as follows:（1）First,we applied the reported protocols to prepare patterned amphiphilic block copolymer brushes on a substrate via light-mediated surface-initiated atom transfer radical polymerization（SI-ATRP）,which could be used as the template to selectively direct the deposition of in situ formed inorganic nanoparticles into the hydrophilic domains.Following this principle,we successfully developed a general and robust strategy for the precise organization of inorganic nanoparticles into arbitrary patterns with tunable dimensions.By changing the pattern of the photomask and experimental conditions for the light-mediated polymerization,inorganic nanostructures with controllable shape and dimensions could be feasibly obtained.Moreover,we demonstrated that this method was also generally applicable to prepare various patterned inorganic nanostructures with different compositions.（2）Using the developed template synthesis strategy,we prepared patterned Au nanostructures of Au nanoparticle assemblies by using patterned poly（（methacryloyloxy）ethyl trimethylammonium chloride）-b-polymethyl methacrylate（PMETAC-b-PMMA）diblock copolymer brushes as the template.In particular,the inner hydrophilic PMETAC domains served as the nanoreactors to guide the in-situ growth of homogeneous and densely packed nanoparticles,while the outer hydrophobic PMMA blocks confined the vertical direction of the nanostructures.We found that such Au nanostructures showed great sensitivity and high signal uniformity as SERS substrates.Impressively,the formation of Au nanostructures with uniformly and densely packed Au nanoparticles resulted a limit of detection（LOD）of 1 f M(10^-15 M),a relatively high average enhanced factor（EF）of 1.1×10⁶,and a low relative standard deviation of 7.2%for 4-acetamidothiophenol（4-AMTP）.In addition,the generality and universality of this patterned Au nanostructure SERS sensor were testified by other four probe molecules,i.e.,4-mercaptobenzoic acid（4-MBA）,Rhodamine 6G（R6G）,methylene blue,and thiram.For these molecules,extremely low detection limits were achieved,ranging from 1f M to 100 p M.（3）Furthermore,we prepared a flexible and sensitive SERS substrate composed of patterned Au nanostructures on a polydimethylsiloxane（PDMS）film.To this end,patterned Au nanostructures on a silicon wafer were transferred onto the PDMS film via the“cut and paste”process enabled by a polyvinyl alcohol（PVA）glue.The resulting hybrid film was utilized to detect 4-MBA,achieving a LOD of 100 p M and an enormous SERS EF of～10⁸.As a demonstration,the flexible SERS substrate was used to detect thiram molecules on actual samples（apple pieces）via the simple“press-peel off”procedure.The detection capability of a trace amount of thiram（1μM）for flexible SERS substrates was validated.Moreover,the sensitivity of the PDMS hybrid film maintained high even after a long-term storage for 30 days,as well as after mechanical deformations including bending and torsion for 100 cycles,which could be attributed to the closely packed Au nanoparticles and the strong attachment between the patterned Au nanostructures and the PDMS film.Such transparent and flexible PDMS hybrid film may have great potentials in the on-site detection of nonplanar surfaces in the practical applications.（4）In the last section,a SERS substrate based on the patterned assemblies of core-shell nanoparticles was prepared following our template synthesis strategy in a facile“one-step”process.To achieve this,patterned Au nanostructures was firstly fabricated and used as the core nanoparticles to grow the silver（Ag）shell.Notably,there was no need for any stabilizers nor time-consuming experimental procedures during the reduction reaction of Ag⁺ions.It was observed that the generated Ag shell layer wrapped the Au core evenly,affordng patterned nanostructures with uniformly and densely packed Ag-coated Au（Ag@Au）nanoparticles.These patterned nanostructures possessed excellent SERS performance with a LOD of 100 p M and an average EF of 8.8×10⁹ for 4-MBA.These experimental results suggested that our template synthesis method could be used to prepare patterned nanoparticle assemblies with complicated compositions.