Large Gold Nanoparticles Research Articles

Toward Fast and Quantitative Modification of Large Gold Nanoparticles by Thiolated DNA: Scaling of Nanoscale Forces, Kinetics, and the Need for Thiol Reduction

We have recently reported on the fast and quantitative adsorption of DNA to 13 nm gold nanoparticles (AuNPs) at pH 3. This is in contrast to most traditional methods at neutral pH, where the adsorption is both slow and requires high excess of DNA. Direct application of our protocol to large particles in many cases did not result in particles that are stable at high (0.3 M) salt, and high excess of DNA was still required for the formation of stable particles. In this work, we investigate the reasons for this limitation on the basis of kinetics and colloidal stability. On the basis of our investigation, fast and quantitative modification of large AuNPs is still possible, either by working at high particle concentration, or by using sonication. As we have shown that fast quantitative modification of large particles is possible, the preparation step of reduction and purification of the thiolated DNA becomes the rate limiting step in the whole AuNP-DNA conjugate protocol. However, we show that this step is unnecessary when using our current protocol.

Mechanistic Investigation of Seeded Growth in Triblock Copolymer Stabilized Gold Nanoparticles

We report the seeded synthesis of gold nanoparticles (GNPs) via the reduction of HAuCl4 by (L31 and F68) triblock copolymer (TBP) mixtures. In the present study, we focused on [TBP]/[Au(III)] ratios of 1-5 (≈1 mM HAuCl4) and seed sizes ~20 nm. Under these conditions, the GNP growth rate is dominated by both the TBP and seed concentrations. With seeding, the final GNP size distributions are bimodal. Increasing the seed concentration (up to ~0.1 nM) decreases the mean particle sizes 10-fold, from ~1000 to 100 nm. The particles in the bimodal distribution are formed by the competitive direct growth in solution and the aggregative growth on the seeds. By monitoring kinetics of GNP growth, we propose that (1) the surface of the GNP seeds embedded in the TBP cavities form catalytic centers for GNP growth and (2) large GNPs are formed by the aggregation of GNP seeds in an autocatalytic growth process.

Thiolate adsorption on Au(${\bm {hkl}}$hkl) and equilibrium shape of large thiolate-covered gold nanoparticles

The adsorption of thiolates on Au surfaces employing density-functional-theory calculations has been studied. The dissociative chemisorption of dimethyl disulfide (CH(3)S-SCH(3)) on 14 different Au(hkl) is used as a model system. We discuss trends on adsorption energies, bond lengths, and bond angles as the surface structure changes, considering every possible Au(hkl) with h, k, l ≤ 3 plus the kinked Au(421). Methanethiolate (CH(3)S-) prefers adsorption on bridge sites on all surfaces considered; hollow and on top sites are highly unfavourable. The interface tensions for Au(hkl)-thiolate interfaces is determined at low coverage. Using the interface tensions in a Wulff construction method, we construct atomistic models for the equilibrium shape of large thiolate-covered gold nanoparticles. Gold atoms in a nanoparticle change their equilibrium positions upon adsorption of thiolates towards shapes of higher sphericity and higher concentration of step-edge atoms.

Sidewall modification of multiwalled carbon nanotubes by Allivum sativum (garlic) and its effect on the deposition of gold nanoparticles

Sidewall modification of multiwalled carbon nanotubes (abbreviated as MWCNTs) was achieved using Allivum sativum (garlic) extract by an acid-free green process. These organosulfur modified-MWCNTs were then decorated with gold nanoparticles and examined by transmission electron microscopy. The presence of organosulfurs over the modified nanotube surface was confirmed. Nanotube surface modification and subsequent presence of thiols as an active linker was confirmed by Raman spectroscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. In the absence of these organosulfurs (thiols), no gold nanoparticle attachment was observed. Both small (1–8nm) and large (12–20nm) gold nanoparticles were found to decorate the modified nanotube surface suggesting coalescence among nanoparticles.

Effects of the Number of Satellites on Surface Plasmon Coupling of Core-Satellite Nanoassemblies

Noble metal nanoparticles have attracted much attention due to their unique optical properties, represented by surface plasmon resonance (SPR). The resonance frequency of the surface plasmon varies with the size, shape, material, and local environment of the nanoparticles. Another appealing means to tune the optical response of the nanoparticle systems is assembling nanoparticles, instead of modifying individual nanoparticles. Coupling of surface plasmons of nanoparticles in close proximity shifts the SPR band of the assembly from that of the individual nanoparticles. The shift naturally depends on the extent of the coupling, and thus on the detailed structure of assemblies such as interparticle distance, allowing for an infinitely fine control of the optical properties. Therefore, assembling nanoparticles in a controlled fashion is of paramount importance. Recently, we developed a novel method to prepare coresatellite nanoassemblies with well-defined and easily controllable structural parameters in a colloidal dispersion state. Selective desorption of large gold nanoparticles (AuNPs) against small AuNPs from glass substrates by sonication led to the production of ultrapure nanoassemblies. The nanoassemblies consist of large core AuNPs decorated by small satellite AuNPs with a distance defined by self-assembled monolayers (SAMs) of alkanedithiol linkers. Different lengths of the alkanedithiol linkers allowed us to measure the surface plasmon couplings between the AuNP core and satellites as a function of the interparticle distances. In complex nanoclusters, the surface plasmon coupling also depends on the number of nanoparticles that constitute the nanoclusters. For example, the surface plasmon coupling band continuously red-shifts as more nanoparticles are assembled in one direction. This is intuitively understood as the red-shifting longitudinal surface plasmon mode supported by elongated nanostructures. Contrary to linear assemblies, core-satellite nanoassemblies can be regarded as multiples of a size-asymmetric heterodimer consisting of a core and a satellite. In this simplified picture, the addition of satellites should not influence the surface plasmon coupling frequencies, although it will increase the intensity of the coupling. In this respect, it is intriguing to experimentally explore the surface plasmon coupling of the core-satellite nanoassemblies as a function of the number of satellites. The new assembly method we developed enables facile control over the number of satellites in the nanoassembly. The following process was used for the production of coresatellite nanoassemblies: (1) surface functionalization of glass substrates with amine, (2) adsorption of core AuNPs (50 ± 5 nm) on the glass substrate, (3) thiol-functionalization of the adsorbed core nanoparticles using 1,10-decanedithiol (DDT) SAMs, (4) adsorption of satellite AuNPs (13 ± 1 nm), and (5) selective desorption of the core-satellite nanoassemblies into ethanol by sonication. The immersion time in step 4, allowed for the satellite AuNPs in solution to interact with the core AuNPs on the glass substrate, determines the number of satellites covering the core nanoparticles (Figure 1(a)). Transmission electron microscopy (TEM) images of more than 100 final core-satellite

Ligand synthesis and passivation for silver and large gold nanoparticles for single-particle-based sensing and spectroscopy.

Silver and large gold nanoparticles are more efficient scatterers than smaller particles, which can be advantageous for a variety of single-particle-based sensing and spectroscopic applications. The increased susceptibility to surface oxidation and the larger surface area of these particles, however, present challenges to colloid stability and controllable bio-conjugation strategies. In this chapter, ligand syntheses and particle passivation procedures for yielding stable and bio-conjugatable colloids of silver and large gold nanoparticles are described.

Enhanced photocatalytic water splitting by BaLa4Ti4O15 loaded with ∼1 nm gold nanoclusters using glutathione-protected Au25 clusters

Glutathione-protected Au25 clusters were used to load monodisperse gold nanoclusters (1.2 ± 0.3 nm) onto BaLa4Ti4O15 to create photocatalysts. The photocatalytic activity of the resulting material for water splitting was determined to be 2.6 times higher than that of catalysts loaded with larger gold nanoparticles (10-30 nm) via conventional photodeposition.

Fast, single-step, and surfactant-free oligonucleotide modification of gold nanoparticles using DNA with a positively charged tail

Fast modification of large gold nanoparticles with DNA is achieved by using DNA with a polycationic tail. The conjugated DNA is available for specific hybridization, and therefore can be used for DNA-based assays or for constructing nanoparticle superstructures based on DNA hybridization.

A Solution to the PEG Dilemma: Efficient Bioconjugation of Large Gold Nanoparticles for Biodiagnostic Applications using Mixed Layers

Gold nanoparticles are of high interest in the biodiagnostic and bioimaging field owing to their unique optical properties such as localized surface plasmon resonance (LSPR) and high Rayleigh scattering efficiency in the visible range. Although biofunctionalization is a prerequirement prior to their integration in diagnostic procedures, aggregation-free conjugation of biomacromolecules to large gold nanoparticle is not trivial. Here, a robust and simple method based on commercially available reactants is reported for the efficient biofunctionalization of gold nanoparticles with sizes ranging from 15 to 175 nm. It is demonstrated that mixed poly(ethylene glycol) (PEG) layers, prepared using specific ratios of low- and high-molecular-weight PEG chains, can be conjugated to proteins and monoclonal antibodies using standard carbodiimide chemistry without detectable aggregation. The properties of the mixed PEG interlayer modified gold nanoparticles were investigated using UV-vis spectrometer, dynamic light scattering, and X-ray photoelectron spectroscopy, which demonstrated the importance of controlling biointerfacial properties. Using the epithelial cell adhesion molecule (EpCAM) as a model target antigen, the benefit of the mixed PEG layers over coatings prepared using high-molecular-weight PEG chains only is demonstrated in vitro using bright field microscopy and reflectance confocal microscopy. Very high binding affinity to breast cancer cells was obtained for the mixed PEG layers. This robust procedure demonstrates that, under optimal conditions, a compromise can be achieved between the excellent steric protection provided by thick PEG adlayers and the high bioconjugation yields afforded by adlayers from low-molecular-weight tethers.

Gold Nanoparticle Deposition on Silica Nanohelices: A New Controllable 3D Substrate in Aqueous Suspension for Optical Sensing

We describe new methods to prepare gold nanoparticle/silica nanohelix hybrid nanostructures which form a 3D network in the aqueous phase. Nanometric silica helices and tubules obtained by sol–gel polycondensation on organic templates of self-assembled amphiphilic molecules were further functionalized with (3-aminopropyl)triethoxysilane (APTES) or (3-mercaptopropyl)triethoxysilane (MPTES). These helices interact strongly with gold nanoparticles (GNPs) of various diameters (1–15 nm). Small GNPs (1–2 nm) at the surface of silica nanohelices grew to about 5 nm when stored in the appropriate organic solvent, whereas this growth process was not observed in water, allowing the size of GNPs at the surface of silica to be controlled by a simple solvent exchange. Larger GNPs (more than 10 nm) at the surface of nano hybrid fibers were used to produce surface enhanced raman scattering (SERS) using benzenthiol as a probe. This provides a novel sustainable approach for designing nanohybrid systems with photonic applications such as ultrasensitive chemical and biological sensors using a simple aqueous suspension of a 3D network of nanohelices.

Design, Synthesis, and Characterization of Mesogenic Amine-Capped Nematic Gold Nanoparticles with Surface-Enhanced Plasmonic Resonances

The use of the liquid-crystalline state to control the assembly of large (>5 nm) gold nanoparticles (NPs) is of considerable interest because of the promise of novel metamaterial properties of such systems. Here we report on a new approach for the preparation of large nematic gold NPs using a bifunctional capping agent that enables control over the particle size and serves as a linkage for subsequent functionalization with mesogenic groups. Properties of the NPs were characterized by HRTEM, NMR, DSC, TGA, UV/vis, OPM, and XRD studies. The results confirmed the formation of a stable nematic mesophase above 37.5 °C for NPs in the 6-11 nm size range.

Evidence for Patchy Lipid Layers on Gold Nanoparticle Surfaces

Gold nanoparticles bearing multiple surface ligands are becoming favored candidates as multifunctional targeting, imaging, and therapeutic vehicles for biomedicine. The question of spatial location of different ligands on nanoparticle surfaces, especially with those of diameters less than 100 nm, is an important one that is difficult to quantitatively address. Here we functionalize the surface of 20, 50, and 90 nm gold nanoparticles with two different lipids, both single and mixed, using two different surface chemical procedures. Mass spectrometry supports the presence of both lipids in the mixed-lipid systems on nanoparticles, while electron microscopy evidence shows domain sizes for one lipid apparently a quarter to a half the projected diameter for 50 and 90 nm particles; but for 20 nm particles, there is no evidence for the existence of patches of the two lipids. Larger gold nanoparticles (90 nm) can be decorated with an array of 12 nm gold nanoparticles by use of a third lipid and antibody-antigen connectors; the display of the 12 nm particles about the 90 nm particles can be controlled to some extent by the initial surface chemistry and is quantified via a new angle analysis procedure.

Click Dendrimers and Triazole-Related Aspects: Catalysts, Mechanism, Synthesis, and Functions. A Bridge between Dendritic Architectures and Nanomaterials

One of the primary recent improvements in molecular chemistry is the now decade-old concept of click chemistry. Typically performed as copper-catalyzed azide-alkyne (CuAAC) Huisgen-type 1,3-cycloadditions, this reaction has many applications in biomedicine and materials science. The application of this chemistry in dendrimer synthesis beyond the zeroth generation and in nanoparticle functionalization requires stoichiometric use of the most common click catalyst, CuSO(4)·5H(2)O with sodium ascorbate. Efforts to develop milder reaction conditions for these substrates have led to the design of polydentate nitrogen ligands. Along these lines, we have described a new, efficient, practical, and easy-to-synthesize catalytic complex, [Cu(I)(hexabenzyltren)]Br, 1 [tren = tris(2-aminoethyl)amine], for the synthesis of relatively large dendrimers and functional gold nanoparticles (AuNPs). This efficient catalyst can be used alone in 0.1% mol amounts for nondendritic click reactions or with the sodium-ascorbate additive, which inhibits aerobic catalyst oxidation. Alternatively, catalytic quantities of the air-stable compounds hexabenzyltren and CuBr added to the click reaction medium can provide analogously satisfactory results. Based on this catalyst as a core, we have also designed and synthesized analogous Cu(I)-centered dendritic catalysts that are much less air-sensitive than 1 and are soluble in organic solvents or in water (depending on the nature of the terminal groups). These multivalent catalysts facilitate efficient click chemistry and exert positive dendritic effects that mimic enzyme activity. We propose a monometallic CuAAC click mechanism for this process. Although the primary use of click chemistry with dendrimers has been to decorate dendrimers with a large number of molecules for medicinal or materials purposes, we are specifically interested in the formation of intradendritic [1,2,3]-triazole heterocycles that coordinate to transition-metal ions via their nitrogen atoms. We describe applications including molecular recognition of anions and cations and the stabilization of transition metal nanoparticles according to a principle pioneered by Crooks with poly(amido amine) (PAMAM) dendrimers, and in particular, the control of structural and reactivity parameters in which the intradendritic [1,2,3]-triazoles and peripheral tripodal tri(ethylene glycol) termini play key roles in the click-dendrimer mediated synthesis and stabilization of gold nanoparticles (AuNPs). By varying these parameters, we have stabilized water-soluble, weakly liganded AuNPs between 1.8 and 50 nm in size and have shown large differences in behavior between AuNPs and PdNPs. Overall, the new catalyst design and the possibilities of click dendrimer chemistry introduce a bridge between dendritic architectures and the world of nanomaterials for multiple applications.

Self-Assembled Plasmonic Dimers of Amphiphilic Gold Nanocrystals

We report a new strategy to assemble large (>40 nm) gold nanoparticles with isotropic surface chemistry into anisotropic plasmonic dimers by taking advantage of the chain reorganization of the amphiphilic polymer brushes grafted on nanoparticle surfaces in selective solvents. Production of high-purity dimers is of considerable interest for applications requiring strong near-field coupling of surface plasmon resonances. The formation of nanoparticle dimers is confirmed by imaging and spectroscopic characterization at both bulk and single-particle levels. The interparticle plasmonic coupling can be reversibly controlled by modulating the assembly/disassembly of the amphiphilic nanocrystals. The general applicability of surface modification of nanocrystals of diverse chemical compositions and morphologies through tandem “grafting to” and “grafting from” reactions offers the possibility to extend this concept to other types of functional nanocrystals.

Influence of Methyl Halide Treatment on Gold Nanoparticles Supported on Activated Carbon

Catalyzing concept: Methyl halides have been used to disperse large (around 20 nm) gold nanoparticles supported on carbon into dispersed gold atoms/dimers at low temperature and atmospheric pressure (see picture). The process occurs through the progressive removal of gold–halogen entities from the metal nanoparticles and a gradual decrease in the size of the gold nanoparticles on the minute timescale.

Tunable subradiant lattice plasmons by out-of-plane dipolar interactions

Plasmonic nanostructures concentrate optical fields into nanoscale volumes, which is useful for plasmonic nanolasers, surface enhanced Raman spectroscopy and white-light generation. However, the short lifetimes of the emissive plasmons correspond to a rapid depletion of the plasmon energy, preventing further enhancement of local optical fields. Dark (subradiant) plasmons have longer lifetimes, but their resonant wavelengths cannot be tuned over a broad wavelength range without changing the overall geometry of the nanostructures. Also, fabrication of the nanostructures cannot be readily scaled because their complex shapes have subwavelength dimensions. Here, we report a new type of subradiant plasmon with a narrow (∼5 nm) resonant linewidth that can be easily tuned by changing the height of large (>100 nm) gold nanoparticles arranged in a two-dimensional array. At resonance, strong coupling between out-of-plane nanoparticle dipolar moments suppresses radiative decay, trapping light in the plane of the array and strongly localizing optical fields on each nanoparticle. This new mechanism can open up applications for subradiant plasmons because height-controlled nanoparticle arrays can be manufactured over wafer-scale areas on a variety of substrates.

Mixed Charged Zwitterionic Self-Assembled Monolayers as a Facile Way to Stabilize Large Gold Nanoparticles

Here we report a facile way of stabilizing large gold nanoparticles (AuNPs) by mixed charged zwitterionic self-assembled monolayers (SAMs). The citrate-capped AuNPs with diameters ranging from 16 nm to even ∼100 nm are well stabilized via a simple place exchange reaction with a 1:1 molar ratio mixture of negatively charged sodium 10-mercaptodecanesulfonic acid (HS-C10-S) and positively charged (10-mercaptodecyl)-trimethyl-ammonium bromide (HS-C10-N4). The 16 nm AuNPs protected by mixed charged zwitterionic SAMs not only show much better stability than the single negatively or positively charged AuNPs, but also exhibit exciting stability as well as those modified by monohydroxy (1-mercaptoundec-11-yl) tetraethylene glycol (HS-C11-EG4). Importantly, 16 nm AuNPs protected by mixed SAMs exhibit good stability in cell culture medium with 10% FBS and strong protein resistance, especially with excellent resistance against plasma adsorption. Moreover, the mixed charged zwitterionic SAMs are also able to well-stabilize larger AuNPs with a diameter of 50 nm, and to help remarkably improve their stability in saline solution compared with HS-C11-EG4 protected ones. When it comes to AuNPs with a diameter of 100 nm, the mixed charged zwitterionic SAM protected nanoparticles retain a smaller hydrodynamic diameter and even better long-term stability than those modified by mercaptopolyethylene glycol (M(w) = 2000, HS-PEG2000). The above results demonstrated that the mixed charged zwitterionic SAMs are able to have a similar effect on stabilizing the large gold nanoparticles just like the single-component zwitterionic SAMs. Concerning its ease of preparation, versatility, and excellent properties, the strategy based on the mixed charged zwitterionic SAM protection might provide a promising method to surface tailoring of nanoparticles for biomedical application.

Thermal-induced growth of gold nanoparticles conjugated with thermoresponsive polymer without chemical reduction

The growth of gold nanoparticles without chemical reduction of gold (III) ions was achieved by the disruption of thermoresponsive polymers conjugated with the gold nanoparticles through the phase transition of the polymers. When a solution of gold nanoparticles coated with thermoresponsive polymers was heated, chains of the thermoresponsive polymers were disrupted because of dehydration, resulting in the fusion of gold nanoparticles to form larger nanoparticles. The evolution of the extinction band around 550nm evidenced the formation of these large (post-fusion) gold nanoparticles, which were characterized by transmission electron microscope (TEM) and dynamic light scattering (DLS). TEM images verified the formation of the large gold nanoparticles having particle sizes of 80–100nm, whereas DLS indicated the existence of large nanoparticles with hydrodynamic diameters exceeding 200nm. The deposition did not require the addition of reductants or trivalent gold ions for the formation of the large gold nanoparticles. Both the heating and the solution conditions were studied to elucidate the mechanism of the formation of large gold nanoparticles.

Antibody-Mediated Self-Limiting Self-Assembly for Quantitative Analysis of Nanoparticle Surfaces by Atomic Force Microscopy

Quantification of very low density molecular coatings on large (60 nm) gold nanoparticles (AuNPs) is demonstrated via the use of antibody-mediated self-limiting self-assembly of small and large AuNPs into raspberry-like structures subsequently imaged by atomic force microscopy (AFM). AFM imaging is proposed as an automated, lower-cost, higher-throughput alternative to immunostaining and imaging by transmission electron microscopy. Synthesis of large AuNPs, containing one of three ligand molecules in one of three stoichiometries (1, 2, or 10 ligands per AuNP), and small probe AuNPs with one of three antibody molecules in a one antibody per AuNP ratio, enabled a range of predicted self-limiting self-assembled structures. A model predicting the probability of observing a given small to large AuNP ratio based on a topography measurement such as AFM is described, in which random orientational deposition is assumed and which accounts for the stochastic synthesis method of the library AuNPs with varied ligand ratios. Experimental data were found to agree very well with the predictive models when using an established AFM sample preparation method that avoids drying-induced aggregation.

Chain length effect of diamine linkers on the self-assembled structure of large gold nanoparticles over glass substrates

Bi-functional diamines with different chain lengths were investigated to control the packing density of large gold nanoparticles (ca. 60–80nm) over glass substrates. Diamine linkers induced the lateral immobilization of neighboring gold nanoparticles (GNPs) on the amine-functionalized glass surface. The molecular bridging force of diamines was proportional to the number of CH2 groups: 1,4-diaminobutane (C-4)<1,8-diaminooctane (C-8)<1,12-diaminododecane (C-12). Even though the aggregation of Au colloids was more sensitive to C-12 diamines, the uniform and densely-packed array of GNPs over glass substrates were accomplished by the addition of C-8 diamines possessing optimal chain length with a balanced binding force on Au colloids.