DNA-directed Assembly Of Multicomponent And Strongly Coupled Metal Nanostructures

At present time,there is little attempts to separate DNA-conjugated non-gold nanoparticles with controlled valences by electrophoresis and programmably assemble discrete multicomponent heterostructure,and assembly of strongly coupled nanoparticles into superstructure has met various difficulties.To address this challenge,we firstly adopted core-shell strategy to obtain stable and dispersed Au @AgNPs and Au@PdNPs,achieving DNA conjugations and gel electrophoresis of these nanoparticles with different valences,and build various nanostructures based on DNA-programmable valence control self-assembly.Furthermore,we assembled Au nanoparticles into supertructure and deposited silver shell to obtain asymmetric heterostructure,which provides platform for developing novel controllable method in core-shell nanostructure synhthesis.Combining strong coupling properties of small molecule with DNA programmable assembly and their compatibility,we achieved programmable construction of strongly coupled nanoparticles into superstructure.In addition,considering the antibacterial activities of Ag nanoparticles and the polyvalent interaction between assembled nanostructure and microbial,we purposively prepared water-dispersible 2D assemblies of Au@ Ag core shell nanoparticles on graphene oxide,and investigated their enhanced antibacterial activity.The resulting materials can be used for innovative nano-bactericides in future.Therefore,my doctoral dissertation mainly focus on the several issues discussed below:1.5 nm AuNPs with a suitable surface functionality are employed as the nucleation seeds to prepare Au@Ag and Au@Pd core-shell nanoparticles(termed as Au@AgNP and Au@PdNP).The existence of AuNP core is the key to controlling the colloidal stability and electrophoretic behavior of a core-shell nanoparticles with a non-gold shell.This allows for a facile gel electrophoretic separation of DNA-conjugated Au@AgNP and Au@PdNP bearing different DNA valences.A further demonstration of valence-controlled and DNA-programmable self-assembly of as-obtained nanoparticle-DNA conjugates into Au@AgNP dimer,Au@PdNP-nAuNP(n=1,2,3)multicomponent heterostructure and Au@PdNP-AuNP core-satellite nanostructures clearly shows the success of our strategy.The resulting DNA-linked nanoparticles can be used as building blocks to construct superstructural nanomaterials.Meanwhile,we discovered BSPP molecules can etch Au@AgNPs during the assembly process.We pointed the difficulties in binary assembly of AgNPs and AuNPs,and tried several strateries to solve these problems.2.We constructed AuNP dimeric heterostructure with different sizes(5 nm and 15 nm)based on DNA-directed assembly process,then we used AuNP dimer as core to deposite Ag shell and investigated the chemical depositon process.We observed that silver chooses to deposite preferentially on bigger AuNP seeds,and the deposition on smaller AuNP was almost suppressed,which was similar to "Mathew effect",resulting asymmetric heterostructure.However,in contrast to dimeric seeds,5 nm AuNPs and 15 nm AuNPs in mixture without DNA assemble behaved nearly equally in silver depositon.It's noteworthy that when distinct nucleation sites are in close,the indued deposition differences can be enlarged obviously,which would affect the morphology of the final products.Motivated by this,multicomponent heterostructure by DNA programmable assembly can be constructed and used as nucleation in chemical deposition towards to prepare multicomponent hybrid nanostructure with novel asymmetric structure.3.The big size and high negative surface charges of DNA molecules makes it difficult to realize a strong coupling among DNA assembled nanoparticles due to its strong steric amd electrostatic repulsion.Considering this challenge,we proposed a strategy compatible with small ion and DNA assembly.We relied highly controllable DNA-directed assembly process to prepare AuNP dimer,and multimer(5 nm AuNP hexamer and 13 nm AuNP pentamer),then silver ions were added to bond with BSPP pre-coated on the nanoparticles so that short-distance coupling is achieved.This simple and efficient "silver soldering" strategy makes strongly coupled nanoparticles assembled on DNA scaffold without compromising their structural programmability.We also found Au@PdNP and AuNP within a dimeric assembly could be tightly soldered together by silver ions.Based on the knowledge gained from structural DNA technology,this strategy can be used to fine tune the optical,electronic and catalysis properties of a coupled system on a DNA platform.4.We prepares bovine serum albumin(BSA)-coated grapheme oxide(GO),and construct 2D AuNP assembly structure on GO by the interaction between BSA and AuNPs.Highly dispersed,stable and water-soluble 2D Au@Ag core-shell nanoparticles can be synthesized based on an electroless deposition of Ag shell on Au nanoparticles pre-assembled on GO.We systematicly charactered the antibacterial activity of the obtained nanostructure based on Escherichia coli(E.coli)system.While neither BSA-GO nor GO@Au show any antibacterial activity,the silver-coated GO@Au nanosheet(GO@Au@Ag)exhibit an enhanced antibacterial activity against E.coli,superior to unassembled Au@ AgNPs and even Ag ions.Such an improvement may be attributed to the increased local concentration of silver nanoparticles around a bacterium and a polyvalent interaction with the bacterial surface.which could be used to rationally design,synthesize and assemble ionnovative and highly active antibacterial nanomaterials.