Letter pubs.acs.org/NanoLett
Nanodroplet-Mediated Assembly of Platinum Nanoparticle Rings in Solution Guanhua Lin,†,‡,§,∥ Xi Zhu,⊥ Utkarsh Anand,†,‡,§,∥ Qi Liu,†,‡,§,∥ Jingyu Lu,†,‡,§,∥ Zainul Aabdin,†,‡,§,∥ Haibin Su,*,⊥ and Utkur Mirsaidov*,†,‡,§,∥ †
Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551 Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546 § Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore, 117543 ∥ NanoCore, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 ⊥ School of Materials Sciences and Engineering, Nanyang Technological University, Singapore 639798 ‡
S Supporting Information *
ABSTRACT: Soft fluidlike nanoscale objects can drive nanoparticle assembly by serving as a scaffold for nanoparticle organization. The intermediate steps in these template-directed nanoscale assemblies are important but remain unresolved. We used real-time in situ transmission electron microscopy to follow the assembly dynamics of platinum nanoparticles into flexible ringlike chains around ethylenediaminetetraacetic acid nanodroplets dispersed in solution. In solution, these nanoring assemblies form via sequential attachment of the nanoparticles to binding sites located along the circumference of the nanodroplets, followed by the rearrangement and reorientation of the attached nanoparticles. Additionally, larger nanoparticle ring assemblies form via the coalescence of smaller ring assemblies. The intermediate steps for ofassembly reported here reveal how fluidlike nanotemplates drive nanoparticle organization, which can aid the future design of new nanomaterials. KEYWORDS: Self-assembly, nanoparticles, in situ TEM, nanodroplet, template-directed assembly
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templated assemblies are based on postassembly characterizations of the end products and do not reveal the intermediate steps important for formation rates and the resultant heterogeneity of the assemblies. For example, the details of how fluidlike templates are populated by nanoparticles, how nanoparticles rearrange after binding and whether such rearrangements promote the attachment of new nanoparticles are largely unknown.22 These questions can be addressed by direct observation of the assembly process. In situ transmission electron microscopy (TEM) imaging has enabled the direct visualization of nanoscale processes in solution,23−25 including the pathways of individual nanocrystal growth,24,26,27 attachment,28−30 aggregation,31,32 and assembly by evaporation,33 and has revealed that the intermediate steps that arise as a result of interparticle interactions play a key role during growth and nanostructure assembly in solution. In these studies, a thin layer of liquid specimen of
