Multiscale Fabrication Of Plasmonic Nanoassemblies For Ultrasensitive Detection

Novel multifunctional metallic nanoparticles exhibit programmable morphology and unique optoelectronic properties.They can be used as building blocks for the construction of nanocrystal-based assembled materials,enabling great practical significance for flexible optoelectronic devices and ultrasensitive SERS detection.In recent years,multi-dimensional plasmonic superlattices have been fabricated,such as‘chiral nano-assemblies',‘polymer-like chain arrays'and‘superlattice crystals'.Meanwhile,the precise construction of hierarchical structures with controllable functions has gradually attracted tremendous attention in this burgeoning field.At the same time,multiscale nanostructures have been fabricated by using‘top-down'guided techniques,which promotes the integration of novel materials with nanofabrication technologies,enabling unique optoelectronic properties,such as localized surface plasmon resonance,plasmon coupling and hybridization,electromagnetic field enhancement,etc.However,accurately assembling"artificial metal atoms"to new nanoassemblies with special array structure and adjustable functionality,through the simple and efficient physical and chemical methods and micro-nano manufacturing technology to are still a very challenging topic.Moreover,high sensitivity and uniformity signal of SERS detection are the bottleneck and difficulty of applying SERS to the field of trace substance detection.To essentially tackle above challenges,this thesis firstly studied the controllable synthesis and assembly of isotropic Au nanopolyhedras(NPGs)and anisotropic nanobricks(NBs),and explored the ordering parameter and SERS performance of the assembled superlattice membranes.In addition,by integrating with silver nanowire(Ag NWs)and magnetic nanoparticles(MNPs),we fabricated plasmonic-based multiscale SERS substrates and studied the cooperative SERS effects.Finally,a simple and effective wrinkle-assisted assembly method(WAS)was developed to fabricatre multiscale patterned plasmonic arrays with macroscopic topological surface and periodic ordered structure for sensitive and uniform SERS detection.The specific contents of the thesis are follows:1.High-quality Au NRs with different aspect ratios were synthesized by using single surfactant and dual surfactants methods.The aspect ratio ranges from 2.4 to 7.2,while the longitudinal peak reaches 1100 nm.NPGs with complex surface morphology and NBs with heterogeneous bimetallic components were synthesized through ligand replacement and further seed growth with Au NRs element as the basic level.Then,the NPGs and NBs were constructed into two-dimensional superlattice films based on the gas-liquid interface method,and the macroscopic and microscopic differences between the films with different elements were explored.The 4-ATP molecule was used as a marker to evaluate the SERS detection performance of the two nano-unit assembled films,and it was found that the NBs membrane had better detection limit and higher sensitivity.2.The NBs film was constructed on a prefabricated Ag nanowire(Ag NWs)substrate to form a multilayered Ag NWs-NB substrate.The pure Ag substrate showed stronger SERS activity,but lower uniformity compared with NBs substrate.Remarkably,the multilayered MNP-NB substrate formed by constructing NBs film on a prefabricated magnetic nanoparticle substrate showed cooperative effects with greatly enhanced SERS intensity.At the same time,after applying the external magnetic field,the in-situ SERS performance was greatly enhanced.3.By using NBs as the building block,a simple and effective wrinkle-assisted self-assembly method(WAS)has been developed combined with the top-down method.Multi-scale patterned arrays were assembled by designing and preparing PDMS templates with periodic structure.The arrays have uniform fringe width and periodic topology,showing extremely strong particle-to-particle coupling and electromagnetic field enhancement effects.In the SERS detection of 4-aminothiophenol(4-ATP)molecules,the detection limit reached the n M scale and the enhancement factor reached the 10~6 level.