Abstract
The capacity to respond or adapt to environmental changes is an intrinsic property of living systems that comprise highly-connected subcomponents communicating through chemical networks. The development of responsive synthetic systems is a relatively new research area that covers different disciplines, among which nanochemistry brings conceptually new demonstrations. Especially attractive are ligand-protected gold nanoparticles, which have been extensively used over the last decade as building blocks in constructing superlattices or dynamic aggregates, under the effect of an applied stimulus. To reflect the importance of surface chemistry and nanoparticle core composition in the dynamic self-assembly of nanoparticles, we provide here an overview of various available stimuli, as tools for synthetic chemists to exploit. Along with this task, the review starts with the use of chemical stimuli such as solvent, pH, gases, metal ions or biomolecules. It then focuses on physical stimuli: temperature, magnetic and electric fields, as well as light. To reflect on the increasing complexity of current architectures, we discuss systems that are responsive to more than one stimulus, to finally encourage further research by proposing future challenges.
Highlights
Introduction a Donostia International PhysicsCenter (DIPC), Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Spain
Using a relatively simple repertoire of building blocks the natural systems have developed a rich variety of sophisticated functions, giving rise to life.[1,2,3,4]
In the presence of relatively high (B15 vol%) amounts of water was the transition to linear assemblies observed. These transitions were reversible: for example, by gradually decreasing the amount of water in a solution of linear aggregates of NPs coated with PS of high molecular weight (50 kDa), a transition to the globular state was observed, followed by disassembly at B2 vol% of water.[21]. These results indicate that solvents can serve as appealing stimuli to direct reversible transitions between different self-assembled states
Summary
Depending mostly on the ligand molecules bound to their surfaces, nanoparticles exhibit good solubility in certain solvents, and poor in others (non-solvents). Localized addition of an organic solvent (THF) onto the interface created a gradient of surface tension, inducing the migration of NPs towards the area of high tension (i.e., away from the place where THF was added) and formation of a densely packed NP monolayer (Fig. 1d, top) This process was associated with a pronounced color change in the NP film from red to purple, indicative of interparticle plasmon coupling. The disassembly– assembly sequence can be repeated more than 100 times without any appreciable fatigue.[31] Notably, the process is associated with a pronounced color change: whereas in the ground state the NPs are quantitatively aggregated and do not contribute to the color of the sample, the light-exposed sample is deep-red due to free Au NPs. The reversible disassembly reaction readily proceeded, in methanolic solutions, and in methanogels based on crosslinked poly(ethylene glycol). Spiropyran-derived photoacids are hydrolytically unstable, and the number of assembly–disassembly cycles in water was limited to B20.32
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