Ag~+-Soldering Based Assembly Of Gold Nanoparticle Clusters With Strongly Coupled Plasmonic Properties

Noble metal nanoparticle assembled structures(also called nanoparticle clusters)are important in applications including photonics,catalysis,molecular sensing and surface enhanced Raman scattering.Gold nanoparticle is one of the most stable metal nanoparticles.Gold nanoparticle has been the hotspot of the research of nanomaterials for its special physical and chemical properties.To develop a simple,rapid and efficient strategy for the preparation of monodisperse nanoparticle clusters in a homogeneous solution is highly desired for the research of metal nanomaterial.My doctoral dissertation mainly focus on the issues as followed:1.A silica nanosphere templated self-assembly in conjunction with Ag+ soldering to fabricate stable and monodisperse gold nanoparticle hollow capsules(colloidosome).The amino-functionalized silica nanospheres are obtained through silylation reaction.In a NaAc/HAc buffer(pH 6.0),the amino groups are protonated,resulting in a positively charged silica surface.Negatively charged BSPP-capped gold nanoparticles are electrostatically adsorbed on the silica surface to form a dense monolayer.The gold nanoparticles are locked together by a Ag+ soldering process.The gold nanoparticle colloidosomes are obtained after removing the silica template.The colloidosomes are then characterized by TEM,SEM and DLS.These results evidence the effectiveness of our strategy.These colloidosomes can be stucturally disrupted by glutathione(GSH),a small chemcial molecule containing sulfhydryl group.The chemoresponsivity of the colloidosomes,along with the inherent tunable shell porosity,is especially desired for molecular sensing and drug delivery in a cellular environment where thiol molecules,for example GSH,are commonly existent.2.The BSPP-capped gold nanoparticles are used to fabricate the discrete strong-coupled nanoparticle clusters throuth the coordination between Ag and BSPP.The clusters with mixed compositions are easily isolatable by agarose gel eclectrophoresis,resulting in mechanically stable and monodisperse nanoparticle dimers in high purify.The gold nanoparticle dimers show excellent sturctural stability after stored in water for over one month and even vigorously sonicated.They are also monodisperse in high ionic strength solutions.We also do a tentative exploration on the formation mechanism of the gold nanoparticle dimers.We find that Ag+ could strip off some BSPP ligands due to a well-known Ag4+ affinity of BSPP.This causes a quick destabilization of nanoparticles to form clustered structures.Immediately,FSDNA gets a chance to interact with the partially exposed(due to BSPP stripping)nanoparticle surface and terminates further clusterizations due to increased steric repulsion.3.We investigate the optical coupling strength and electic field enhancement of the dimeric structures based on the optical extinction specra and Raman scattering spectra.The optical extinction spectra of dimers is significantly different from that of monomers when the diameter of the gold nanoparticle is greater than 13.3 nm.A new plasmon resonances appears at the infrared area.And these new peaks rapidly redshift with increased particle size.For AuNPs(24.1 and 37.5 nm),completely separated longitudinal resonances are observed.During to the strong optical coupling strength of dimers,the electromagnetic field at the sub-nm gap(near field)of the Au dimers is dramatically boosted,resulting in a significant enhancement of the Raman scattering signals of 4-mercaptopyridine absorbed on the surface of dimers.The average Raman enhancement factor(EF)of the 37.5 nm dimers is estimated to be 5×105.We have developed a new strategy to produce disrete strongly coupled nanoparticle oligomers based on a novel "Ag+ soldering" triggered rapid and controllable nanoparticle assembly.Our results will benefit many fundamental and frontier research areas including light scattering,bio-imaging,molecular sensing.