The Oil/water Interfacial Self-Assembly Of Gold And Silver Nanostructures And Its Applications

Noble metal nanoparticles have unique physical and chemical properties, which are very different to the bulk materials. They can be used to develop applications such as sensors, optical imaging, electronic devices, nanocatalysis and so on. However, how to assemble various types of noble nanoparticles into large scale of two-dimentional(2D) nanomembrane is still challenging, especially in the applications of flexiable plamsonics, anti-counterfeiting labels and pesticides detection. In this thesis, we devoted to develop a general method to assemble various types of noble nanoparticles into 2D superlattice, and try to put it into the pratical uses, such as flexible plasmonics, and anti-counterfeiting techniques and trace detection.We report on a facile interfacial self-assembly approach to fabricate large-scale metal nanoparticle superlattice sheets from various types of nanoparticles, such as the Au@Ag core-shell nanocubes(NCs), Au@Ag core-shell nanocuboids(NBs), nanocages and Au nanorods(NRs). Polyvinylpyrrolidone(PVP) was used as the negative surfactant to reduce the surface charge density. When the ethanol was injected, metal nanoparticle will spontaneously self-assemble at the oil/water interface for about 13cm2. The mirror nanomembrane can be explored as the novel SERS substrates with high SERS activities, and reproducible Raman signals. Moreover, the superlattice formed from nanocages exhibits positive recyclable nanocatalysis nanosheets. With assistant of Na BH4, 4-nitrophenol can be reduced into 4-aminophenol when the metal nanoparticles exist. After 5 times recycle, the catalytic efficiency maintain same, which is almost 2 times better than that of monometallic nanoparticle nanosheet.With the integration of superlattice mirror with elastomeric substarates enables fabrication of flexible/stretchable plasmonic devices that can be conformable attached to curved surfaces, which is otherwise impossible to achieve with the current predominantly rigid plasmonic nanostructure. The flexible plasmonic devices exhibited reversible plasmonic responses to repeated mechanical stretching. Under stretching, the dominant plasmonic resonance peak for both Au@Ag core/shell nanocuboid(NB) and Au@Ag core/shell NC superlattice sheets shifted to blue, following a power-law function of the applied strain. Interestingly, the power-law exponent(or the decay rate) showed a strong shape dependence, where a faster rate was observed for NB superlattice sheets than that for NC superlattice sheets. We further study the streching mechanism of NC in theory by CST Microwave Studio TM Suite. The NC flexible superlattice nanosheet was mainly dominated by Longitudinally stretched model.We further propose the concept on dual coding superlattice sheets for anticounterfeiting labels: plasmonic coding and SERS coding. The bottom up technique is a general method for various types of nanoparticles and Raman codes, and can fabricated larger scale of anti-counterfeiting nanosheets on PDMS patterns through the 3D printing technique. The SERS acitivity is 10 times higher comparing to the traditional SERS sheets, which greatly improve the reading sensitivity of Raman coding. Furthermore, the SERS dual coding labels exibit the mechanical and chemical stabilities. After 100 times bending tests, the Raman barcod almost maintain the same, which no literature report the results. Raman singal is still very strong after 75 days prepared. The dual coding sheets can also used on kinds of substrates, such as the printing papers, plastic bags, and bank notes.Moreover, we systematically investigated the size- and shape-dependent SERS activities of plasmonic core–shell nanoparticles towards detection of the pesticide thiram. Monodisperse Au@Ag nanocubes(NCs) and Au@Ag nanocuboids(NBs) were synthesized and their Ag shell thickness was precisely adjusted from ~1nm to ~16 nm. All these nanoparticles were used as SERS substrates for thiram detection, and the Raman intensities with three different lasers(514 nm, 633 nm and 782 nm) were recorded and compared. Our results clearly show that: the excitation wavelength discriminated particle shapes regardless of particle sizes, and the maximized Raman enhancement was observed when the excitation wavelength approaches the SERS peak( provided there is significant local electric field confinement on the plasmonic nanostructures at that wavelength); at the optimized laser wavelength, the maximum Raman enhancement was achieved at a certain threshold of particle size(or silver coating thickness). By exciting particles at their optimized sizes with the corresponding optimized laser wavelengths, we achieved a detection limit of roughly around 0.24 ppb and 0.19 ppb for NCs and NBs, respectively.In summary, we devoted to develop a general method to assemble various types of noble nanoparticles into 2D superlattice, and explored the potential applications such as the highly functional SERS substrates, recyclable nanocatalysis nanosheets, flexible plamsonics nanosheets, anti-counterfeiting labels and extremely sensitive trace detection.