title: Interactions and Attachment Pathways between Functionalized Gold Nanorods.
abstract: Nanoparticle (NP) self-assembly has been recognized as an important technological process for forming ordered nanostructures. However, the detailed dynamics of the assembly processes remain poorly understood. Using in situ liquid cell transmission electron microscopy, we describe the assembly modes of gold (Au) nanorods (NRs) in solution mediated by hydrogen bonding between NR-bound cysteamine linker molecules. Our observations reveal that by tuning the linker concentration, two different NR assembly modes can be achieved. These assembly modes proceed via the (1) end-to-end and (2) side-to-side attachment of NRs at low and high linker concentrations in solution, respectively. In addition, our time-resolved observations reveal that the side-to-side NR assemblies can occur through two different pathways: (i) prealigned attachment, where two Au NRs prealign to be parallel prior to assembly, and (ii) postattachment alignment, where two Au NRs first undergo end-to-end attachment and pivot around the attachment point to form the side-to-side assembly. We attributed the observed assembly modes to the distribution of linkers on the NR surfaces and the electrostatic interactions between the NRs. The intermediate steps in the assembly reported here reveal how the shape and surface functionalities of NPs drive their self-assembly, which is important for the rational design of hierarchical nanostructures.
authors.affiliation: Department of Physics, National University of Singapore , 117551 Singapore.|Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore , 117557 Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 117546 Singapore.
authors.forename: Shu Fen
authors.initials: SF
authors.lastname: Tan
authors.affiliation: Department of Physics, National University of Singapore , 117551 Singapore.|Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore , 117557 Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 117546 Singapore.|NUSNNI-NanoCore, National University of Singapore , 117411 Singapore.
authors.forename: Utkarsh
authors.initials: U
authors.lastname: Anand
authors.affiliation: Department of Physics, National University of Singapore , 117551 Singapore.|Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore , 117557 Singapore.|Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore , 117546 Singapore.|NUSNNI-NanoCore, National University of Singapore , 117411 Singapore.
authors.forename: Utkur
authors.identifier: 0000-0001-8673-466X
authors.initials: U
authors.lastname: Mirsaidov
keywords: in situ TEM; intermolecular forces; linker-mediated assembly; nanorods; self-assembly