Self‐Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness

Abstract

Gold nanoparticles (AuNP) with pyridyl end-capped polystyrenes (PS-4VP) as "quasi-monodentate" ligands self-assemble into ordered PS-4VP/AuNP nanostructures with 3D hexagonal spatial order in the dried solid state. The key for the formation of these ordered structures is the modulation of the ratio AuNP versus ligands, which proves the importance of ligand design and quantity for the preparation of novel ordered polymer/metal nanoparticle conjugates. Although the assemblies of PS-4VP/AuNP in dispersion lack in high dimensional order, strong plasmonic interactions are observed due to close contact of AuNP. Applying temperature as an external stimulus allows the reversible distortion of plasmonic interactions within the AuNP nanocomposite structures, which can be observed directly by naked eye. The modulation of the macroscopic optical properties accompanied by this structural distortion of plasmonic interaction opens up very interesting sensoric applications.

Plasmonic Properties of Colloidal Assemblies

“…[ 88 ] Starting from spherical primary gold NPs, enhanced absorbance in the near‐IR tissue transparency window (a wavelength range in which electromagnetic radiation can penetrate comparably deep into biological tissue), can be achieved upon aggregation. [ 88 ] The extent of cluster formation can as well be controlled by external triggers which address a functional polymer coating, for instance by adjusting temperature [ 21,22 ] and by applying light. [ 41,42 ] Coumarin‐containing polymer ligands for example can be used for photochemical NP crosslinking (via [2+2]‐cycloaddition reaction) and the cluster dis‐assembly (via cycloreversion at higher photon energies).…”

“…If only the size of an isolated particle is changed, the properties illustrated in Figure 1a can be obtained: With increasing size, the plasmonic resonance shifts to higher wavelengths (lower energy). Determined by the dielectric constant of the metal, the [15][16][17][18][19][20] polystyrene; [21,22] star block copolymers of poly(N-isopropylacrylamide) and poly(N,N-dimethylacrylamide); [23] poly(N-isopropylamide-co-allylacetic acid); [24] poly[(di(ethylene glycol) ethyl ether acrylate-co-oligoethylene glycol acrylate)-block-(N-(3-(dimethylamino)propyl) methacrylamide)]; [25] poly(ethylene glycol) [26] pH Poly(aniline); [27][28][29] poly(allylamine); [30] poly(dimethylaminoethyl methacrylate); [31] poly(N-isopropylamide-co-allylacetic acid) [24] Redox reaction Poly(aniline) [32,33,28] Solvent environment Polystyrene; [34][35][36][37] poly(styrene-block-(4-vinylbenzoic acid)); [38] poly(methyl methacrylate) [39] Light Spiropyran-containing poly(methacrylate); [40] azobenzene-containing poly(methacrylate); [41] block-copolymers with coumarin-containing poly(methacrylate) blocks [42] Figure 1. a) Simulation of gold monomers, dimers, and trimers with a diameter of the individual nanoparticles between 15 and 60 nm.…”

Redispersible Gold Nanoparticle/Polymer Composite Powders Ready for Ligand Exchange Reactions

“…Therefore, functionalization of the nanoparticles with other ligands afterwards provides versatile possibilities. The two‐phase ligand exchange is literature known and a well established method ,. At the aqueous organic interface, a weak ligand can be substituted with a strong binding ligand via transfer of the presynthesized nanoparticles whereby the nanoparticles obtain new functionality.…”

“…Regardless of the choice for the preparation of redispersible encapsulated nanoparticles, further processing is limited, in particular when the nanoparticles are stabilized by ligands for aqueous media. In many cases ligand exchange reactions with nanoparticles are an important method in order to transfer nanoparticles from the aqueous phase to an organic media so as to perform follow‐up organic reactions ,. Due to the high binding strength of powder forming ligands to nanoparticles in aqueous phase, ligand exchange reactions to ligands solved in organic media are still an unresolved challenge.…”

Photobiologically Directed Assembly of Gold Nanoparticles

“…[9] Moreover, AuNPs of various shapes and sizes were ordered and arranged in defined architectures. [5][6][7][8][9][10][11][12] Nanoparticle assembly was for instance controlled by various ligands, [13][14][15] but also by external stimuli, such as magnetic fields or light. [16][17][18][19][20][21][22][23][24] These advances notwithstanding, the controlled higherorder assembly in response to external cues remains challenging, but worthwhile to explore because it could significantly extend the application scope of AuNPs.…”