Tailor-made Plasmonic Gold Nanostructures Based On DNA Origami

Metallic nanostructures that support surface plasmons are of great interest because of their ability to manipulate light at nanoscale.The special surface plasmonic resonances arising from coupling between adjacent nanoparticles bring new optical functions and offer potentials for the constructions of metamaterials,nanocircuits,sensors and subwavelength waveguides.Especially,the strong field localization at defined positions(hot spots)leads to spectroscopic enhancements that in principle fulfills the single-molecular level detection.As an emerged alternate approach,DNA origami based antennas have gained considerable attention owing to the inherent feature of 4-6 nm spatial resolution that can be employed for positioning both plasmonic nanoparticles and organic dyes.Therefore,DNA origami is hopefully an excellent platform for next-generation plasmonic devices while more efforts should be focused on increasing the complexity of plasmonic patterns.Here we report a general and robust strategy for assembling large AuNPs and anisotropic nanoparticles into complex plasmonic clusters on DNA origami templates with high precision and yield.So this work can be divided into two parts,the first part mainly study the intrinsic properties of the DNA origami,including chapters 2,3 and 4.The second part mainly study the self-assembly of gold nanoparticles,including chapters 5,6 and 7.The DNA origami template used in Chapter 5 and 7 are based on the structures prepared in Chapter 2.In chapter 2,we demonstrate a strategy to scale up DNA origami technology.Various dimer,trimer,tetramer,hexamer and infinite linear structures are constructed successfully.The DNA origami templates used in Chapter 5 and 7 are based on the structures prepared in Chapter 2.In chapter 3,the response of different DNA origami nanostructures to the widely used short-wavelength UV(UVC)radiation has been systematically investigated.It is found that origami deformation with increased UV doses underwent a general pathway of expansion,distortion,and final disintegration,regardless of shape and size.However,the deformation speed varied greatly from each typical origami and was found to be strongly related to the number of strand nicks.Based on the observations,an inherent structural continuity-dependent mechanism was proposed.In chapter 4,the response of DNA origami nanostructures to pH influence is systematically investigated from two aspects.At first,the self-assembly ability of DNA origami triangle in different p H buffer is tested,and the origami structure could be formed in the pH range of 6-9.Then,the pH tolerance of DNA origami to the external environments is investigated by immersing the successfully prepared origami(pH=8)into acidic and basic solutions for different hours.The AFM results indicates that the DNA origami could maintain its original structure for at least 12 hours in the pH range of 5-10.In chapter 5,we report a general and robust strategy for assembling large AuNPs into complex plasmonic clusters on DNA origami templates with high precision and yield.The 80 nm AuNPs structure has displayed a typical Fano resonance behavior that can provide large field enhancements.The strong optical coupling allows us to demonstrate its ability of being sensitive antenna for surface enhanced Raman scattering(SERS).Most importantly,it is found that specific number of Raman molecules even down to single molecule could be characterized.In chapter 6 and 7,we first develop a high yield shape-selective purification method of gold nanoprisms with DNA-assist.Then the purified gold nanoprisms are used as anisotropic building blocks for the bottom-up materials engineering.Bowtie structures with various predetermined angles and inter-particle distances are constructed with high efficiency.These discrete anisotropic metallic nanostructures exhibit unique plasmonic properties.