DNA Directed Self-assembly Of AuNPs And Their Dark Field Light Scattering Property

Noble metal nanoparticle clusters are widely used in biosensing,catalysis,photonics and surface-enhanced Raman scattering.Gold nanoparticles are one of the most stable metal nanomaterials,and have become a research hotspot due to their unique local surface plasmon resonance?LSPR?characteristics and stability.It is of great significance to find a fast and efficient method for self-assembly of monodisperse gold nanoparticle clusters and to study their light scattering properties for the performance regulation and application of metal nanomaterials.DNA has the advantages of addressability and programability.The DNA double helix structure has good rigidity,and the self-assembly of the double helix structure can be controlled by adjusting the number and sequence of bases.Therefore,the DNA structure is a good regulator for regulating the aggregation of nanoparticles.Compared to the traditional"top-down"self-assembly method,the"bottom-up"self-assembly method makes it easier to achieve precise regulation and assembly of nano-unit.DNA nanotechnology takes DNA molecule out of its biological context and uses its information to assemble structural motifs.DNA nanostructures are of great significance in directing the assembly of nanoparticles.The specific research contents of this paper are as follows:?1?Gold nanoparticles capped by BSPP ligands are used as structural units,and the strong coordination of Ag⁺and BSPP is used to rapidly aggregate gold nanoparticles.The SSDNA in solution rapidly adsorbs to the surface of the gold nanoparticles,preventing its infinite aggregation,thereby synthesizing monodisperse gold nanoparticle dimers,trimers and tetramers.The obtained Au dimers,trimers and tetramers were separated and characterized by agarose gel electrophoresis,and then co-localized by scanning electron microscopy and dark field microscopy to perform morphological characterization and dark field imaging.At the same,their non-polarized scattering spectrums are obtained by the spectrograph.In addition,dark field imaging under different polarized light is acquired through changing the polarization angle of the incident light,and the intensity of the scattered light is calculated using IPP software.For Au tetramers,RGB analysis was also performed on the dark field imaging under polarized light to quantify the scattered light color.?2?DNA tetrahedral nanocage directed self-assembly of AuNPⁱⁿ⁵(AuNP^out10)₄and their characterization.DNA strands are purified and quantified before use.Three DNA strands of L,M,and S are annealed to form a triangular star motif.Mg²⁺concentration and incubation temperature were optimized to increase the yield of the triangular star motif.DNA tetrahedral nanocage with a tail was assembled by first formation of triangular star motif and further cohesion through sticky end.Separation and characterization of DNA tetrahedral nanocage with a tail were performed by native polyacrylamide gel electrophoresis.Next,functionalized DNA modification of gold nanoparticles was carried out using the classical salt aging method.After the modification is completed,the absorption spectrum is measured and used to calculate the concentration and determine whether the modification of the thiol DNA strand is successful.The DNA functionalized gold nanoparticles are then incubated with the DNA tetrahedral nanocage with the tail chain,so that the gold nanoparticles are encapsulated in the DNA tetrahedral nanocage by the base pairing of DNA strands of the thiol DNA with the tail chain of the DNA tetrahedron nanocage.Finally,it was characterized by agarose gel electrophoresis.In summary:?1?The self-assembly of AuNP dimer,trimer,tetramer are assisted by Ag⁺soldering method.Agarose gel characterization shows several clear bands corresponding to them.The method is simple and efficient,and the obtained gold nanoparticles have good stability and high dispersion.Trimers and tetramers were co-localized by scanning electron microscopy and dark field microscopy.It was found that gold nanoparticle trimers and tetramers exhibited structural diversity,and different structures have especial LSPR properties.For the trimers,the scattering spectra change regularly with the increasing ratio of long axis to short axis?a/b?.The peak-sharing phenomenon decreases with the increase of a/b,at the same time,the scattering light intensity increases.When two large particle sizes and one small particle size gold nanoparticles are agglomerated,there is no obvious peak splitting phenomenon.For tetramers,AuNP tetramer with a/b=1.12 has no splitting peaks;AuNP tetramer with a/b=1.44 has one main peak and two acromions in the scattering spectrum;AuNP tetramer with a/b=3.37 has a small acromion beside the main peak of gold nanoparticle tetramers,and the splitting phenomenon is very weak.For polarized light Scattering of AuNP trimers and tetramers,it was found that the value of a/b of trimers had a great influence on the scattering intensity under different polarized light.The intensity difference between transverse plasma resonance and longitudinal plasma resonance increases with the increase of the value of a/b.When the incident light is parallel to the long axis of the particle,the scattered light intensity is the largest,and the scattered light intensity is the smallest when the incident light is parallel to the short axis of the particle.Combining the polar coordinates of tetramers and RGB images,it is found that the intensity of scattered light can be judged preliminarily according to the color of scattered light.?2?Base on three single strands of DNA with different sequences,DNA triangular star motif was self-assembled by precise proportional regulation,and then cohesized to DNA tetrahedral nanocage.It was found that 17.5 mM Mg²⁺concentration and slow annealing increased the yield of the three-point-star DNA motif.Then,the DNA tetrahedral nanocage with tail chain was obtained by self-assembly of three-point-star DNA motif?75 nM?in 17.5 mM Mg²⁺buffer through slow annealing.Subsequently,the functionalized DNA modification of gold nanoparticles was carried out by classical salt aging method.The UV-vis absorption spectra was used for characterization.The maximum absorption wavelengths of AuNPⁱⁿ⁵-DNA/DNA2 and AuNP^out10-DNA2C/T5SH were red-shifted about 5 nm,which was consistent with the theoretical value.Next,the tetrahedral nanocage with a tail was incubated with AuNPⁱⁿ⁵-DNA/DNA2 and AuNP^out10-DNA2C/T5SH.After agarose gel characterization,it was found that AuNPⁱⁿ⁵ was encapsulated in the cavity of DNA tetrahedral nanocage.Most assembled structures were mainly AuNPⁱⁿ⁵(AuNP^out10)₄,and a small amount of AuNPⁱⁿ⁵(AuNP^out10)₃ and AuNPⁱⁿ⁵(AuNP^out10)₅ were observed under transmission electron microscopy.