Evaporation‐Induced Ordered Honeycomb Structures of Gold Nanoparticles at the Air/Water Interface

The breath figure method was used to prepare dodecanethiol‐capped gold nanoparticle macroporous structures with pore diameters from 1.7 to 3.5 μm on an air/water interface. A two‐step procedure is proposed for the fabrication of these macroporous structures, by forming a surfactant monolayer on water, and drop‐casting a gold nanoparticle dispersion in chloroform onto the surfactant monolayer. The self‐assembled films are easily transferred from the water surface onto different substrates and were characterized by TEM, SEM, and AFM. Ordered honeycomb structures with different pore arrays (perforated monolayer films, hexagonal networks and alveoli‐like porous films) were obtained. The change in morphology is concentration dependent, and deformed structures with elliptic honeycomb networks are also observed. In addition, honeycomb films using gold nanoparticles stabilized by a weakly bound ligand (dioctadecyldimethylammonium chloride) were formed by the same technique. These films have potential as substrates for surface‐enhanced Raman spectroscopy.     

Hamilton Receptor‐Mediated Self‐Assembly of Orthogonally Functionalized Au and TiO2 Nanoparticles

A new prototype of reversible self‐assembly between functionalized gold and titanium dioxide nanoparticles (NPs) utilizing hydrogen bonding interactions was developed and established. The gold nanoparticles were functionalized with a Hamilton‐receptor functionality bearing a thiol moiety as anchoring group. The titanium dioxide nanoparticles were modified with cyanurate derivatives which contained phosphonic acids as anchoring groups. The host–guest type interaction between two functionalized nanoparticles yielded a highly integrated nanoparticle system in chloroform. Moreover, by presenting a competing ligand in an exchange reaction, the product of self‐assembly can be segregated into the individual soluble components of functionalized nanoparticles. The self‐assembly and the exchange reaction were followed and monitored in detail by UV/Vis spectroscopy. The structure of the self‐assembly product was investigated using scanning electron microscopy (SEM) and small‐angle X‐ray scattering (SAXS).     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005     

Rapid Cationization of Gold Nanoparticles by Two‐Step Phase Transfer

Cationic gold nanoparticles offer intriguing opportunities as drug carriers and building blocks for self‐assembled systems. Despite major progress on gold nanoparticle research in general, the synthesis of cationic gold particles larger than 5 nm remains a major challenge, although these species would give a significantly larger plasmonic response compared to smaller cationic gold nanoparticles. Herein we present the first reported synthesis of cationic gold nanoparticles with tunable sizes between 8–20 nm, prepared by a rapid two‐step phase‐transfer protocol starting from simple citrate‐capped particles. These cationic particles form ordered self‐assembled structures with negatively charged biological components through electrostatic interactions.     

Real‐Time Monitoring of Phosphorylation Kinetics with Self‐Assembled Nano‐oscillators

Phosphorylation is a post‐translational modification that is involved in many basic cellular processes and diseases, but is difficult to detect in real time with existing technologies. A label‐free detection of phosphorylation is reported in real time with self‐assembled nano‐oscillators. Each nano‐oscillator consists of a gold nanoparticle tethered to a gold surface with a molecular linker. When the nanoparticle is charged, the nano‐oscillator can be driven into oscillation with an electric field and detected with a plasmonic imaging approach. The nano‐oscillators measure charge change associated with phosphorylation of peptides attached onto a single nanoparticle, allowing us to study the dynamic process of phosphorylation in real time without antibodies down to a few molecules, from which Michaelis and catalytic rate constants are determined.     

Controlled Release of a Sparingly Water‐Soluble Anticancer Drug through pH‐Responsive Functionalized Gold‐Nanoparticle‐Decorated Liposomes

The binding and detachment of carboxyl‐modified gold nanoparticles from liposomes is used for controlled drug delivery. This study reveals that the binding and detachment of nanoparticles from liposomes depends on the degree of hydration of the liposomes. Liposomes with a lower hydration level undergo stronger electrostatic interactions with negatively charged gold nanoparticles, thus leading to a slower detachment of the carboxyl‐modified gold nanoparticles under gastric conditions. Therefore, under gastric conditions, gold‐nanoparticle‐decorated dipalmitoylphosphatidylcholine (DPPC) liposomes exhibit an at least ten‐times‐slower drug release compared to gold‐nanoparticle‐decorated 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (DMPC) liposomes, although both liposomes in the bare state fail to pursue controlled release. Our study also reveals that one can modulate the drug‐release rate by simply varying the concentration of nanoparticles. This study highlights a novel strategy for the controlled release of drug molecules from liposomes.     

Stabilization and Large Nonlinearity of Gold Nanoparticles Functionalized with a π‐Conjugated Polymer

Gold nanoparticles protected by a novel π‐conjugated polymer [poly(p‐phenylene ethynylene) containing pendent disulfide and bipyridine groups] are synthesized and characterized. The polymer can stabilize the gold nanoparticles effectively. The nonlinear optical properties of the gold nanoparticle colloid solutions in toluene are investigated by using the Z‐scan technique at a wavelength of 532 nm and pulse width of 4 ns. The gold‐nanoparticle colloid solutions show an exceptional nonlinear absorption effect, which simultaneously contains the saturated absorption resulting from third‐order nonlinearity and a large reverse‐saturated absorption resulting from fifth‐order nonlinearity. In addition, asymmetric self‐focusing refractive effects are investigated in the colloid solutions.     

Self‐assembly of polymer‐coated ferromagnetic nanoparticles into mesoscopic polymer chains

The self‐assembly of dispersed polymer‐coated ferromagnetic nanoparticles into micron‐sized one‐dimensional mesostructures at a liquid–liquid interface was reported. When polystyrene‐coated Co nanoparticles (19 nm) are driven to an oil/water interface under zero‐field conditions, long (≈ 5 μm) chain‐like assemblies spontaneously form because of dipolar associations between the ferromagnetic nanoparticles. Direct imaging of the magnetic assembly process was achieved using a recently developed platform consisting of a biphasic oil/water system in which the oil phase was flash‐cured within 1 s upon ultraviolet light exposure. The nanoparticle assemblies embedded in the crosslinked phase were then imaged using atomic force microscopy. The effects of time, temperature, and colloid concentration on the self‐assembly process of dipolar nanoparticles were then investigated. Variation of either assembly time t or temperature T was found to be an interchangeable effect in the 1D organization process. Because of the dependence of chain length on the assembly conditions, we observed striking similarities between 1D nanoparticle self‐assembly and polymerization of small molecule monomers. This is the first in‐depth study of the parameters affecting the self‐assembly of dispersed, dipolar nanoparticles into extended mesostructures in the absence of a magnetic field. © 2008 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 46: 2267–2277, 2008     

Direct Cytosolic Delivery of siRNA Using Nanoparticle‐Stabilized Nanocapsules

The use of nanoparticle‐stabilized nanocapsules (NPSCs) for the direct cytosolic delivery of siRNA is reported. In this approach, siRNA is complexed with cationic arginine‐functionalized gold nanoparticles by electrostatic interactions, with the resulting ensemble self‐assembled onto the surface of fatty acid nanodroplets to form a NPSC/siRNA nanocomplex. The complex rapidly delivers siRNA into the cytosol through membrane fusion, a mechanism supported by cellular uptake studies. Using destabilized green fluorescent protein (deGFP) as a target, 90 % knockdown was observed in HEK293 cells. Moreover, the delivery of siRNA targeting polo‐like kinase 1 (siPLK1) efficiently silenced PLK1 expression in cancer cells with concomitant cytotoxicity.     

Seed‐Mediated Synthesis of Single‐Crystal Gold Nanospheres with Controlled Diameters in the Range 5–30 nm and their Self‐Assembly upon Dilution

Single‐crystal gold nanospheres with controlled diameters in the range 5–30 nm were synthesized by using a facile approach that was based on successive seed‐mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self‐assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water.     

Polysiloxanes Modified by Thiol‐Ene Reaction and Their Interaction with Gold Nanoparticles

A poly(vinylmethyl‐co‐dimethyl)siloxane has been functionalized with phenylethanethiol, N‐methylmercaptoacetamide and heptadecafluoro‐1‐decanethiol by a thermal radical thiol‐ene reaction initiated by azobisisobutyronitrile. The resulting polymers were obtained in good yields with most of the time a complete conversion of the vinyl groups. The reaction also preserved the fragile polysiloxane backbone. The polymer, grafted with about 25 % of mercapto‐acetamide groups is soluble in polar solvents such as dimethylformamide and dimethyl sulfoxide, opening the way for further functionalization with polar molecules such as unprotected carbohydrates. Spherical and branched gold nanoparticles were coated with these polymers. This coating induced a surface resonance plasmon shift resulting from the interaction of the grafted polysiloxanes with the nanoparticle surface. The shift can be explained by the variation of the refractive index of the side groups but may be also related to the self‐organization of polysiloxanes and their interactions with the gold surface depending on their polarity.     

Light‐Driven Self‐Healing of Nanoparticle‐Based Metamolecules

Metamolecules and crystals consisting of nanoscale building blocks offer rich models to study colloidal chemistry, materials science, and photonics. Herein we demonstrate the self‐assembly of colloidal Ag nanoparticles into quasi‐one‐dimensional metamolecules with an intriguing self‐healing ability in a linearly polarized optical field. By investigating the spatial stability of the metamolecules, we found that the origin of self‐healing is the inhomogeneous interparticle electrodynamic interactions enhanced by the formation of unusual nanoparticle dimers, which minimize the free energy of the whole structure. The equilibrium configuration and self‐healing behavior can be further tuned by modifying the electrical double layers surrounding the nanoparticles. Our results reveal a unique route to build self‐healing colloidal structures assembled from simple metal nanoparticles. This approach could potentially lead to reconfigurable plasmonic devices for photonic and sensing applications.     

Bottom-up assembly of colloidal gold and silver nanostructures for designable plasmonic structures and metamaterials

We report on bottom-up assembly routes for fabricating plasmonic structures and metamaterials composed of colloidal gold and silver nanostructures, such as nanoparticles ("metatoms") and shape-controlled nanocrystals. Owing to their well-controlled sizes/shapes, facile surface functionalization, and excellent plasmonic properties in the visible and near-infrared regions, these nanoparticles and nanocrystals are excellent building blocks of plasmonic structures and metamaterials for optical applications. Recently, we have utilized two kinds of bottom-up techniques (i.e., multiple-probe-based nanomanipulation and layer-by-layer self-assembly) to fabricate strongly coupled plasmonic dimers, one-dimensional (1D) chains, and large-scale two-dimensional/three-dimensional (2D/3D) nanoparticle supercrystals. These coupled nanoparticle/nanocrystal assemblies exhibit unique and tunable plasmonic properties, depending on the material composition, size/shape, intergap distance, the number of composing nanoparticles/nanocrystals (1D chains), and the nanoparticle layer number in the case of 3D nanoparticle supercrystals. By studying these coupled nanoparticle/nanocrystal assemblies, the fundamental plasmonic metamaterial effects could be investigated in detail under well-prepared and previously unexplored experimental settings.     

Self‐Assembly Mechanism of Nanoparticles of Ni‐Based Prussian Blue Analogues at the Air/Liquid Interface: A Synchrotron X‐ray Reflectivity Study

Prussian Blue analogue (PBA) nanoparticles can be self‐assembled at air/liquid interfaces to build novel materials with interesting magnetic features. Herein, we study the influence of the size of PBA Cs_0.4Ni[Cr(CN)₆]_0.9 and K_0.25Ni[Fe(CN)₆]_0.75 nanoparticles on the self‐assembly behavior by synchrotron X‐ray reflectivity. Both nanoparticles show similar Z‐potential values. The phospholipid dipalmitoylphosphatidylcholine and the amino surfactant dimethyldioctadecylammonium have been used as Langmuir monolayers to anchor the PBA nanoparticles and study the interplay of forces directing the self‐assembly of the nanoparticles at the surfactant/liquid interface. Whereas Cs_0.4Ni[Cr(CN)₆]_0.9 nanoparticles with a diameter of 8 nm form an incomplete layer at the surfactant/water interface, the larger K_0.25Ni[Fe(CN)₆]_0.75 nanoparticles with a diameter of 20 nm generate complete layers that can be stacked to one another. The size of the PBA nanoparticles is the main parameter determining the final arrangement at the air/liquid interface, due to the different extent of interparticle interaction. This study aims at the rationale design of PBA nanoparticles for an effective interfacial self‐assembly, ultimately leading to functional materials.     

Designing superhydrophobic surface based on fluoropolymer–silica nanocomposite via RAFT‐mediated polymerization‐induced self‐assembly

Superhydrophobic surfaces (SHS) find versatile applications as coatings due to their very high water‐repellency, self‐cleaning, and anti‐icing properties. This investigation describes the preparation of a SHS from surfactant‐free hybrid fluoropolymer latex. In this case, reversible addition‐fragmentation chain transfer (RAFT) polymerization was adopted to prepare a copolymer of 4‐vinyl pyridine (4VP) and vinyl triethoxysilane (VTES), where the pyridine units were quaternized to make the copolymer soluble in water. The copolymer was further used as a macro‐RAFT agent to polymerize 2,2,2‐trifluoroethyl methacrylate (TFEMA) in a surfactant‐free emulsion via polymerization‐induced self‐assembly (PISA). The macro‐RAFT agent contained a small amount of VTES as co‐monomer which was utilized to graft silica nanoparticles (SNPs) onto the P(TFEMA) spheres. The film prepared using the nanocomposite latex exhibited a nano‐structured surface as observed by SEM and AFM analyses. Surface modification of the film with fluorinated trichlorosilane produced an SHS with a water contact angle (WCA) of 151.5°. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 266–275     

Polystyrene‐Core–Silica‐Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles

Polystyrene‐core–silica‐shell hybrid particles were synthesized by combining the self‐assembly of nanoparticles and the polymer with a silica coating strategy. The core–shell hybrid particles are composed of gold‐nanoparticle‐decorated polystyrene (PS‐AuNP) colloids as the core and silica particles as the shell. PS‐AuNP colloids were generated by the self‐assembly of the PS‐grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the “free” PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe₃O₄ nanoparticles were encapsulated in the core, which resulted in magnetic core–shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high‐temperature catalysis and as nanoreactors.     

High‐Yield Excited Triplet States in Pentacene Self‐Assembled Monolayers on Gold Nanoparticles through Singlet Exciton Fission

One of the major drawbacks of organic‐dye‐modified self‐assembled monolayers on metal nanoparticles when employed for efficient use of light energy is the fact that singlet excited states on dye molecules can be easily deactivated by means of energy transfer to the metal surface. In this study, a series of 6,13‐bis(triisopropylsilylethynyl)pentacene–alkanethiolate monolayer protected gold nanoparticles with different particle sizes and alkane chain lengths were successfully synthesized and were employed for the efficient generation of excited triplet states of the pentacene derivatives by singlet fission. Time‐resolved transient absorption measurements revealed the formation of excited triplet states in high yield (172±26 %) by suppressing energy transfer to the gold surface.     

Directed Self‐Assembly of Diblock Copolymer Thin Films on Prepatterned Metal Nanoarrays

The sequential layer by layer self‐assembly of block copolymer (BCP) nanopatterns is an effective approach to construct 3D nanostructures. Here large‐scale highly ordered metal nano­arrays prepared from solvent annealed thin films of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) diblock copolymer are used to direct the assembly of the same BCP. The influence of initial loading concentration of metal precursor, the type of metal nanoparticle (gold, platinum, and silver), and the nanoparticle–substrate interaction on the directed assembly behavior of the upper BCP layer have been focused. It is found that the upper BCP film can be completely directed by the gold nanoarray with P2VP domain exclusively located between two adjacent gold nanowires or nanodots, which behaves the same way as on the platinum nanoarray. While the silver nanoarray can be destroyed during the upper BCP self‐assembly with the silver nanoparticles assembled into the P2VP domain. Based on the discussions of the surface energy of nanoparticles and the interplay between nanoparticle–substrate interaction and nanoparticle–polymer interaction, it is concluded that the effect of immobilization of nanoparticles on the substrate, together with entropy effect to minimize the energetically unfavorable chain stretching contributes to the most effective alignment between each layer.

     

Zn2+‐Regulated Self‐Sorting and Mixing of Phosphates and Carboxylates on the Surface of Functionalized Gold Nanoparticles

Herein, we describe the self‐sorting of phosphate‐ and carboxylate‐containing molecules on the surface of monolayer‐protected gold nanoparticles. Self‐sorting is driven by selective interactions between the phosphate probe and Zn²⁺ complexes in one monolayer; these interactions force the carboxylate probe to move to a second type of nanoparticle. This process effectively separates the probes and causes their localization in well‐defined spaces surrounding the nanoparticles. The removal/addition of Zn²⁺ metal ions from the system is used to convert the system from an ordered to a disordered state and vice versa. The possibility to control the location and transport of populations of molecules in a complex mixture creates new perspectives for the development of innovative complex catalytic systems that mimic nature.