Large Nanoparticle Aggregates Research Articles

Electromagnetic enhancement spectra of one-dimensional plasmonic hotspots along silver nanowire dimer derived via surface-enhanced fluorescence.

We developed a spectroscopic method for directly obtaining the spectra of electromagnetic (EM) enhancement of plasmonic hotspots (HSs). The method was applied to one-dimensional (1D) HSs generated between silver nanowire (NW) dimers. The EM enhancement spectra were derived by dividing the spectra of surface-enhanced fluorescence (SEF) from single NW dimers with SEF obtained from large nanoparticle aggregates, where aggregate-by-aggregate variations in the SEF spectra were averaged out. Some NW dimers were found to exhibit EM enhancement spectra that deviated from the plasmon resonance Rayleigh scattering spectra, indicating that their EM enhancement was not generated by superradiant plasmons. These experimental results were examined by numerical calculation based on the EM mechanism by varying the morphology of NW dimers. The calculations reproduced the spectral deviations as the NW diameter dependence of EM enhancement. Phase analysis of the enhanced EM near-fields along the 1D HSs revealed that the dipole-quadrupole coupled plasmon, which is a subradiant mode, mainly generates EM enhancement for dimers with NW diameters larger than ∼80nm, which was consistent with scanning electron microscopic measurements.

Enhanced sodium and potassium ions storage of soft carbon by a S/O co-doped strategy

The development of soft carbon based anode for sodium and potassium ion batteries (SIBs and PIBs) is hindered by the slow charge storage dynamics due to the larger ionic Na+/K+ size. Various strategies, including pore structure regulation and heteroatom doping, have been reported to enhance the batteries performance but sacrificing initial coulombic efficiency. Herein, a simple ball mill-thermal treatment method is developed to prepare S/O co-doped soft carbons (SO-SC) using 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as precursor. The ball-milling process is helpful for the morphology change from small irregular shapes to the large nanoparticle aggregates, which is beneficial for the decrease of electrolyte/electrode contact area, thus enhancing the initial coulombic efficiency (ICE). Besides, the sulfur and oxygen doped sites are introduced into the carbon structure, which enlarge the interlayer distance and increase the Na+ or K+ coordinate sites. Thanks to these desirable characteristics, the SO-SC for the SIB anode delivers a high ICE of 61.3% and superior rate capability (230.7 mAh g−1 at 2 A g−1). A high capacity retention of 86.9% after 4000 cycles is also demonstrated. Furthermore, when applied as PIBs anode, the SO-SC also delivers a high capacity of 412.6 mAh g−1, remarkable rate performance and cyclic performance.

Insights on ligand interactions with titanium dioxide nanoparticles via dynamic light scattering and electrophoretic light scattering

Titanium dioxide nanoparticles (NPs) have become widely used and studied in industry, cosmetics, and water treatment; however, due to their surface charge and composition, uncoated nanoparticles often aggregate and settle in a solution. This leads to loss of function and suspension, abandoning the NPs' properties that make them ideal for many applications. Loss of NP suspension can also complicate analysis of solutions containing nanoparticles. Therefore, titanium dioxide nanoparticles are good candidates for surface coatings that enable hydrophilic interactions and improved suspension. Many coating processes require complex synthesis methods and begin with titanium dioxide precursors rather than with already synthesized nanoparticles. The method presented herein examines additive processes that may increase suspension capabilities and inhibit loss of function through aggregation of large nanoparticles (50±25nm). Nineteen chelating organic compounds were tested via a 1, 2, or 3 equivalent additions to pristine, unmodified TiO2 nanoparticles in solution. Furthermore, ligands that showed the best chelating behavior were diluted and the pH was modified to understand pH dependent behavior. Dynamic light scattering and electrophoretic light scattering were used in the study of the chemical behavior of the modified TiO2 nanoparticles. Results show that nanoparticles interacting with dimethylethanolamine, dimercaptosuccinic acid, sodium citrate, dimethylglyoxime, and oxalic acid showed improved ζ-potential at a pH of 5. Physico-chemical processes are discussed in the understanding of these results.

ZnO nanostructures produced by pulsed laser deposition in open air

The paper presents a study on the fabrication of ZnO nanostructures by applying a pulsed laser deposition technique in air at atmospheric pressure (in open air). The laser ablation of a ZnO target was performed by a nanosecond Nd:YAG laser system operated at the wavelengths of 355, 532 and 1064 nm. In open air, the ablation process leads to a direct deposition of nanoparticles and nanoparticle aggregates formed in the plasma plume. The deposition of the nanostructured material on the substrate resulted in the growth of a highly porous structure. The influence was investigated of the wavelength used for ablation on the morphology, composition and optical properties of the samples. The ultraviolet ablation resulted in deposition of a structure which mainly consists of nanoparticle aggregates and separate nanoparticles. Deposition by visible light formed a highly porous structure consisting of aggregated nanoparticles. Conducting the ablation process with infrared radiation resulted in the growth of a complex 3D structure consisting of large nanoparticle aggregates. The presence of a small amount of nitrogen was detected in all samples independently of the wavelength used for ablation. It was found that the different wavelengths used for ablation lead to fabrication of ZnO structures with different morphology and different types of surface defects, which defines the photoluminescence properties of the samples. The porous structure observed in the ZnO samples, combined with their optical properties, suggests that such nanostructures could be used for efficient fabrication of sensor devices.

Host–Guest and Electrostatic Interactions in Supramolecular Nanoparticle Clusters

The influence of the charge, structure, and host–guest interactions of different soft polymeric components on their assembly with negatively charged inorganic gold and up‐converting nanoparticles (NPs) functionalized with cyclodextrins (CD‐AuNPs and CD‐UCNPs) was studied. The inter‐/intramolecular interplay was evaluated by changing the morphology and the charge of the polymeric component. Use of a linear, anionic guest‐functionalized polymer resulted in the formation of thin coating layers around the CD‐AuNPs and CD‐UCNPs without further NP aggregation. When the branched cationic polymer poly(ethylene imine) (PEI) was used instead, small clusters were obtained before the electrostatic neutralization point, whereas large NP aggregates were obtained above the neutralization point. When branched cationic guest‐functionalized dendrimers were used, clusters were obtained at a 1:1 host/guest stoichiometry. In this case, self‐assembly occurred when still far away from the neutrality point, indicating that this cluster formation is driven by supramolecular host–guest interactions. The luminescence of the CD‐UCNPs with the linear polymer was quenched due to C–H vibrational modes of the guest polymer, whereas in the case of electrostatic cluster formation by PEI the luminescence of CD‐UCNPs was enhanced after the neutralization point, due to the formation of densely packed NP assemblies. These findings should be useful for the design of hybrid polymeric–inorganic assemblies for sensing and biomedical applications.

Biological effects of TiO2 and CeO2 nanoparticles on the growth, photosynthetic activity, and cellular components of a marine diatom Phaeodactylum tricornutum

It is very important to have a good understanding of the biological effects of nanoparticles (NPs) on marine diatoms. In this study, the physiological and biochemical responses of a marine diatom Phaeodactylum tricornutum to titanium dioxide NPs (nano-TiO2) and cerium oxide NPs (nano-CeO2) were compared and evaluated using 96h growth tests in a batch-culture system. At 96h of exposure, the growth inhibition rate (IR, %) of P. tricornutum increased from 5.46 to 27.31% with increasing nano-TiO2 concentrations from 2.5 to 40mgL−1. The maximum IR of 49.59% occurred in 40mgL−1 nano-TiO2 treatments at 48h of exposure. Growth of the diatom was increased in low nano-CeO2 treatments (≤5mgL−1), but was inhibited in high nano-CeO2 treatments (≥10mgL−1). Large aggregates of NPs were attached to the cells of P. tricornutum in 20 and 40mgL−1 nano-TiO2 and nano-CeO2 treatments. In addition, the effective quantum yields (ΦPSII) of P. tricornutum in 40mgL−1 nano-TiO2 and nano-CeO2 treatments were 83.33 and 71.13% of that in the controls at 96h of exposure, respectively. Compared with that of the controls at 96h of exposure, chlorophyll a content, soluble sugar content, malondialdehyde (MDA) content, SOD and POD activities of P. tricornutum in 40mgL−1 nano-TiO2 and nano-CeO2 treatments increased by 57.56, 142.97, 373.25, 698.76, 204.85% and 21.43, 89.41, 194.97, 340.05, 502.86%, while soluble protein content decreased by 70.38 and 28.64%, respectively. These findings will be helpful to understand the effect mechanisms of NPs on marine organisms.

Experimental study of surface-modified silica nanoparticles in enhancing oil recovery

One of the main objectives of nanotechnology in the oil industry is to identify applications that could bring significant benefits to enhanced oil recovery. Therefore, it has attracted the attention of many researchers over the last decade. This paper experimentally investigates the efficiency of surface-modified silica nanoparticles in enhanced oil recovery. These nanoparticles improve oil recovery through two main mechanisms: oil–water interfacial tension reduction; and wettability alteration. Various concentrations of nanofluid were made, and their effect on wettability and interfacial tension were investigated to determine the optimum concentration for injection into core samples. The results indicate that a concentration of 4 g l −1 is the optimum concentration. Moreover, this paper reports the nanofluids’ potential in enhanced oil recovery of water-wet core plugs. The results of coreflood experiments reveal that oil recovery increases by 26.2% and total oil recovery considerably improves after the injection of nanofluid. In addition, filtration of the nanofluid before injection into the core was very effective in reducing the risk of possible permeability damage that occurred due to the deposition of large nanoparticle aggregates onto the rock surface.

Integral equation theory for atactic polystyrene nanocomposite melts with a multi-site model.

In this work, a multi-site chain model was incorporated into the polymer reference interaction site model to investigate the structure and properties of atactic polystyrene (aPS) melt and the structural correlations of dilute spherical nanoparticles dissolved in aPS melt. The theoretically calculated X-ray scattering intensities, solubility parameters and intermolecular correlation functions of aPS and its nanocomposites are found to be in agreement with the corresponding molecular simulation and experimental data. The theory was further employed to investigate the distribution functions of different size effects of aPS-nanoparticle system with consideration of the potential of mean force and depletion force. The aggregation of large nanoparticles increases with the increase of the nanoparticle-site size ratio in the infinitely dilute limit. The results show that the present theory can be used to investigate the structure of aPS melt and its nanocomposite, and give a further understanding of the filler dispersion and aggregation. All the observations indicate molecular-level details of the underlying mechanisms, providing useful information for the future design control of new aPS-nanocomposite materials with tailored properties.

Oriented Gold Nanoparticle Aggregation for Colorimetric Sensors with Surprisingly High Analytical Figures of Merit

The common drawbacks of current colorimetric sensors using gold nanoparticle aggregation is its relatively low sensitivity and narrow dynamic range, which restrict their application in real sample analysis when competing with other analytical techniques such as fluorescence and chemiluminescence. In this article, we demonstrate a novel strategy to construct colorimetric sensors based on gold nanoparticle aggregation. Unlike the conventional colorimetric sensors which cause the formation of large nanoparticle aggregates, in our strategy, dimers are selectively formed upon target binding, which results in significantly improved long-term stability and a more than 2 orders of magnitude wider dynamic range of detection than that of the conventional colorimetric sensors. In addition, a strategy to minimize the interparticle gap through the formation of a Y-shaped DNA duplex enables to increase the limit of detection by 10,000 times. The analytical figures of merit of the proposed sensor are comparable to those of the fluorescence-based sensors.

Maturation and demise of human primary monocytes by carbon nanotubes

The possibility of exploiting carbon nanotubes (CNT) in biomedical practices requires thorough analysis of the chemical or bulk effects they may exert on the immune system, the complex network that recognizes and eliminates foreign particles. In particular, the phagocytosing ability of cells belonging to the monocyte/macrophage lineage may render these immune cells an ideal toxicological target of pristine CNT, which may form aggregates of size exceeding monocyte/macrophage phagocytosing plasticity. To shed light on this issue, we analyzed the effects that pristine multi-walled CNT (MWCNT) without metal or biological impurities exert on survival and activation of freshly explanted human peripheral blood monocytes, analyzing in parallel the non-phagocytosing lymphocytes, and using graphite as control carbon material. MWCNT (diameter 10–50 nm, length up to 10 μm) exert two different toxic effects on mononuclear leukocytes: a minor apoptogenic effect (on lymphocytes > monocytes), and a major, apoptosis-independent effect that exclusively and deeply affect monocyte homeostasis. Analysis of monocyte number, adhesion, redox equilibrium, and the differentiation markers CD14 and CD11b reveals that MWCNT cause the selective disappearance of phagocytosis-competent monocytes by mechanisms related to the presence of large nanoparticle aggregates, suggesting phenomena of bulk toxicity possibly consisting of frustrated phagocytosis. At the same time, MWCNT stimulate adhesion of the phagocytosis-incompetent monocytes, and their differentiation toward a peculiar maturation asset. These observations point out novel mechanisms of CNT toxicity, renewing concerns that they may impair the innate immune system deranging the inflammatory responses.

Living Fungi Cells Encapsulated in Polyelectrolyte Shells Doped with Metal Nanoparticles

We report the layer-by-layer coating of living fungi cells (Saccharomyces cerevisiae and Trichoderma asperellum) with polyelectrolytes poly(allylamine hydrochloride)/sodium poly(styrene sulfonate) and bovine serum albumin/DNA and citrate-stabilized gold and silver nanoparticles. It was found that the nanoparticles were effectively incorporated between oppositely charged polyelectrolyte layers, modifying the topography and the roughness of cell walls. The formation of large aggregates of nanoparticles on the cell walls of encapsulated cells was shown. It was found that the encapsulated cells preserved their viability and the shells were soft enough to allow the growth of mycelium. The surface-enhanced Raman scattering (SERS) was used to investigate the biochemical environments of the gold and silver nanoparticles immobilized on the surface of T. asperellum conidia. The SERS spectra from encapsulated conidia and polyelectrolytes indicate that both gold and silver nanoparticles interact with cell walls from different locations, and nanoparticle-polyelectrolyte interaction is limited. The approach described in this paper might have potential applications in modification of living cells.

Simulation of the growth of nanoparticle aggregates reproducing their natural structure in disperse systems

A three-dimensional continuum model of the generation of aggregates of spherical particles is developed that allows us to reproduce natural conditions of structure formation in real disperse systems with an arbitrary viscosity of a dispersion medium. The exchange between translational and rotational degrees of freedom for aggregates, subaggregates, and single particles at an arbitrary interparticle interaction potential, as well as at the preset functions of the distribution over particle sizes and thicknesses of the adsorption layer, is taken into account in the model. The interaction potential of the particles includes electrostatic (among them, screened), elastic, and van der Waals interactions and allows for the effect of external electric, magnetic, and gravitational fields. Structural and statistical characteristics of aggregates formed at different stages of particle coagulation are studied, and the quasi-ordering of single subaggregates in the elastic adsorption layer of particles is revealed. The model can be applied to the study of optical absorption by large aggregates of nanoparticles with natural structure and the kinetics of sol aggregation as functions of the properties of the adsorption layer of particles and the action of external physical factors.

Structure and effective interactions in polymer nanocomposite melts: An integral equation theory study

The polymer reference interaction site model from integral equation theory is used to investigate the structure and effective interactions in polymer nanocomposite melts where strong nanoparticle-monomer interactions are principally considered in this work. For finite particle volume fraction, the compromise for the interference between polymers and nanoparticles results in an optimum particle volume fraction for nanoparticle dispersion in polymer melts. At constant particle volume fraction, the effects of degree of polymerization become insignificant when it reaches a threshold value, below which quantitative effects on the organization states of polymer nanocomposite melts are found and help nanoparticles to well disperse in polymer. The aggregation of large nanoparticles decreases with the increase of the nanoparticle-monomer attraction strength. These observations may provide useful information for the development of new polymer materials.