Construction Of DNA Origami-based Plasmonic Nanostructures And Their Applications In SERS

The unique physical and chemical properties of plasmonic nanostructures make them widely used in microelectronics,optical devices,biosensing,and other fields,especially metal nanostructures such as gold and silver.In recent years,precise arrangement of metal nanoparticles in space has been crucial for creating advanced plasmonic nanostructures with tailored optical responses and new functions.Top-down methods are widely used to create metal nanostructures with precise positions and shapes,including lithography,photolithography,and so on.Nevertheless,these techniques have limited resolution,which is difficult to achieve sub-10 nm gaps,as well as limitations such as high instrumentation costs,complex fabrication steps,and difficulty in achieving complex threedimensional nanostructures.With the rapid development of DNA nanotechnology in recent years,DNA can be used not only as the genetic material of life,but also as a self-assembly tool to build nanostructures.Compared with top-down methods,DNA nanostructures,especially DNA origami,can provide highly programmable templates to assemble molecules or nanoparticles into precise patterns with nanoscale addressability,and are widely used in biological detection,drug delivery,optical devices,etc.However,the DNA origami templates to construct plasmonic nanostructures are dominated by spherical nanoparticles,which create a limited variety of nanostructures and make it difficult to realize applications with complex optical response.In contrast,anisotropic metal nanoparticles have tunable optical properties,but the construction of plasmonic nanostructures by controlling anisotropic metal nanoparticles is still a challenge.Based on this,the research of this thesis is to assemble plasmonic nanostructures with precise geometrical configurations of tailored optical responses by DNA origami templates and anisotropic metal nanoparticles as the basic building blocks,,and use them as platforms to explore SERS sensing.Specifically,it is divided into the following three parts:1.Hierarchical assembly to construct chained gold nanocube(Au NC)nanostructures and their applications in surface enhanced Raman scattering(SERS)Generally,DNA origami nanostructures are assembled by folding a long single-stranded scaffold with multiple short DNA strands through the principle of complementary base pairing,which provide a programmable way to construct metal nanostructures.However,the dimension of DNA origami is usually limited by the length of the single-stranded scaffold,thus limiting their versatility as assembly templates to construct metal nanostructures.The hierarchical assembly technique of DNA origami provides a solution to this problem.We achieved hierarchical assembly of DNA origami by specifically designing complementary DNA strands at the edges of DNA origami to create largerscale,controllable DNA origami multimeric structures.Furthermore,by assembling Au NCs on DNA origami templates followed by hierarchical assembly,the construction of chained Au NC nanostructures with precisely controllable number of Au NCs that break through the dimension limitation of DNA origami monomers are realized,and these Au NC nanostructures realized significant amplification of the SERS signal.2.Pattern recognition directed assembly of plasmonic gap nanostructures for singlemolecule SERSAnisotropic Au NCs with tunable localized plasmon resonance properties are good materials for constructing plasmonic gap nanostructures with tailored optical responses.However,creating shapecontrollable nanogaps between Au NCs remains challenging,and the addressability of DNA nanostructures provides a solution.Based on this,we designed a DNA origami directed pattern recognition strategy to assemble Au NCs into plasmonic gap nanostructures.By designing DNA capture strands that form specific patterns on the surface of DNA origami,different geometrical configurations of plasmonic gap nanostructures with nanometer-precise and shape-controllable gaps are created.Hot spots can be created in these gaps due to localized field enhancement.Taking advantage of the addressability of DNA origami,Raman probe molecules are specifically placed in hotspot regions to realized SERS detection at the single-molecule level,which are consistent with the finite difference time domain(FDTD)simulation results.3.DNA nanoprinting technology to assemble plasmonic nanostructures and their singlemolecule SERS applicationsThe vertices,edges,and faces of anisotropic Au NCs make it possible to create a variety of plasmonic nanostructures with different configurations.Precisely functionalization of Au NCs with relative spatial directionality and sequence asymmetry is a major challenge,but it offers rich fundamental research and optical application possibilities.Based on this,we designed a DNA origami-based nanoprinting strategy to transfer DNA strands with predefined sequences,positions and numbers on the surface of DNA origami to the surface of Au NCs to form specific functionalized Au NCs.These functional DNA strands are capable of further assembly,and gold nanoparticles(Au NPs)were captured in this study to create a series of Au NC-Au NP nanostructures with controllable stereo geometry and composition,and generate hot spots in the nanogaps.By anchoring the single Raman probe molecules in the hot spot region,the significantly enhanced electromagnetic field at the hot spot arouses the amplification of the SERS signal of a single molecule.