DNA Nanostructure-based Gold Nanoparticle Assembly And Their Plasmonic Properties

The surface plasmon resonance(SPR)properties of gold nanoparticles are closely related to the sizes,spacings,morphologies and compositions of the particles,and the gold nanoparticle assemblies are widely used in biological detection and analysis because of their excellent optical properties,stable chemical compositions and good biocompatibility.So far,the main preparation methods of gold nanostructures are including top-down etch and bottom-up self-assembly,the latter is more simple and more low-cost,but it is difficult to prepare discrete gold nanostructures by using ordinary self-assembly method,however,the emergence of DNA origami provides the opportunity to solve this problem.DNA origami structures comprise a long scaffold strand and hundreds of short staple strands,and these nanostructures can be used as templates for the precise assemblies of gold nanoparticles because each one of the staple strands is completely addressable.The main content of this paper is to assemble gold nanoparticles(Au NPs)by using DNA nanostructures and then to study their surface plasmon resonance properties through the surface enhanced Raman scattering(SERS),the details are as follows: 1.We employed a two-dimensional rectangular DNA origami as platform to construct a gold nanoparticle rolling system: one gold nanoparticle was immobilized as a reference,and the other gold nanoparticle was driven to roll unidirectionally by strand replacement reaction.The whole dynamic process was characterized by atomic force microscope(AFM).At first,the two gold nanoparticles were on the same axis,which had the smallest spacing and the strongest plasmon resonance,however,as the rolling process went on,the spacing was bigger and bigger,and the plasmon resonance was weaker and weaker.This phenomenon was consistent with the SERS signal detection result.2.The resolution of DNA origami is only 6 nanometers,which has a great limitation on adjusting the spacings of gold nanoparticles,but the circular DNA double helix is an ideal candidate structure with the resolution of 2 nanometers.We first used enzyme to synthesize 96 nt circular single-stranded DNA molecules,which acted as scaffold strands to hybridize with the predesigned staple strands in order to form DNA nanotubes.The nanotubes are composed of three lateral circular DNA double helixes with a length of about 9 nanometers and a diameter of about 10 nanometers.Furthermore,by extending the staple strands as linker strands,we used the DNA nanotube monomers as basic units to construct the structures of trimer,tetramer and tetrahedral tetramer.These structures were characterized by polyacrylamide gel electrophoresis(PAGE)because of their small sizes,and the bands of all the target structures could be clearly observed.3.The DNA nanotube monomer,trimer,tetramer and tetrahedral tetramer have good rigidity and can adjust the distances between gold nanoparticles well.We used these structures to assemble gold nanoparticles so as to construct gold nanoparticle dimer,trimer,tetramer and tetrahedral tetramer,and all the plasmonic nanostructures were purified by agarose gel electrophoresis(AGE)and characterized by transmission electron microscope(TEM),then the yields of all structures were counted.In addition,we also detected the SERS signal of gold nanoparticle dimer structures and found that they had good surface plasmon resonance properties.