Orientation dependence of optical activity in light scattering by nanoparticle clusters

The optical properties of nanoparticle clusters vary with the spatial arrangement of the constituent particles, but also the overall orientation of the cluster with respect to the incident light. This...

Dispersion Dynamics of Clustered Particles by Centrifugal Force

In this paper an approach is proposed to solve the problem of aggregation in nanomaterials through the mean of rotational separation aiming to quickly disperse clustered nanoparticles while not affecting their purity. If it is possible, this approach may replace the current mean of mechanical mixing, which may cause impurities issues. The hypothesis is that the centrifugal force due to rotational velocity acting on the nanoparticles can overcome the cohesive force between the nanoparticles, therefore dispersing the clustered nanoparticles. The experimental mean is to put different spheres connected by different types of glues imitating different nanoparticle clusters into centrifuges imitating the swivel plate. The results from both the theoretical model and the experiment show that for a cluster with a cohesive force of 1.75N, a rotational velocity of about 800rad./s is required to disperse the cluster. While for a cluster with a cohesive force of 0.25N and the same mass and position, a rotational velocity of about 150 rad./s is required to disperse the cluster. Except for the cohesive force, the mass and position of the nanoparticle on the swivel plate also have a large effect on the required rotational velocity. The observation of the physical mechanism of the dispersion has also shown that while using this way, the cluster is dispersed slowly with small parts separated from it. Therefore, this way can also eliminate re-clustering problems of nanoparticles.

Assembling Nanoparticle Clusters by Kinetic Control Using Weakly Interacting DNA

In this paper, we describe the use of weakly interacting DNA linkages to assemble nanoparticles into defined clusters. Gold nanoparticles (AuNPs) were synthesized and functionalized with thiol modified single-stranded DNA (ssDNA) and hybridized with ssDNA linkers of a defined length (L). The self-assembly kinetics were altered by manipulating interparticle energetics through changes to linker length, rigidity, and sequence. The linker length regulated the hybridization energy between complementary AuNPs, were longer L increased adhesion, resulting in classical uncontrollable aggregation. In contrast, L of six complementary bases decreased adhesion and resulting in slower nucleation that promoted small cluster formation, the growth of which was studied at two assembly temperatures. Results indicated that a decrease in temperature to 15 oC increased cluster yield with L6 as compared to 25 oC. Finally, the clusters were separated from unassembled AuNPs by sucrose gradient ultracentrifugation (UC) and studied via UV-visible spectrophotometry (UV-vis), dynamic light scattering (DLS) and transmission electron microscopy (TEM).

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stiffness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiments and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.

Photothermal ablation of murine melanomas by Fe3O4 nanoparticle clusters

Melanoma is one of the deadliest forms of cancer, for which therapeutic regimens are usually limited by the development of resistance. Here, we fabricated the Fe3O4 nanoparticle clusters (NPCs) that have drawn widespread attention and investigated their role in the treatment of melanoma by photothermal therapy (PTT). Transmission electron microscopy imaging shows that our synthesized NPCs are spherically shaped with an averaged diameter of 329.2 nm. They are highly absorptive at the near-infrared 808 nm wavelength and efficient at converting light into local heat. In vitro experiments using light-field microscopy and MTT assay showed that Fe3O4 NPCs, in conjunction with near-infrared irradiation, effectively ablated A375 melanoma cells by inducing overt apoptosis. Consistently, in vivo studies using BALB/c mice found that intratumoral administration of Fe3O4 NPCs and concomitant in situ exposure to near-infrared light significantly inhibited growth of implanted tumor xenografts. Finally, we revealed, by experimental approaches including semi-quantitative PCR, western blot and immunohistochemistry, the heat shock protein HSP70 to be upregulated in response to PTT, suggesting this chaperone protein could be a plausible underlying mechanism for the observed therapeutic outcome. Altogether, our results highlight the promise of Fe3O4 NPCs as a new PTT option to treat melanoma.

Framboid Sizes

Framboid size-frequency plots show log-normal distributions with a geometric mean diameter of 6.0 μ‎m and with 95% of framboids ranging between 2.9 and 12.3 μ‎m. The largest framboids may be 250 μ‎m in diameter, although spherical aggregates of framboids, known as polyframboids, may range up to 900 μ‎m in diameter. Various spherical clusters of nanoparticles have been described which are less than 0.2 μ‎m in diameter. These do not form a continuum with framboids. There is no evidence for any significant change in framboid diameters with geologic time, and the differences in mean sizes between hydrothermal and sedimentary framboids do not, at present, appear to be statistically significant. By contrast, it appears that the mean diameters of framboids from non-marine sediments are significantly larger (7.6 μ‎m) than marine framboids (5.7 μ‎m). There is some evidence that framboids formed in the water column are smaller than those formed in sediments, but the non-critical use of this possible difference as a proxy for paleoenvironmental reconstructions is not robust. So-called microframboids and nanoframboids are discrete entities which are distinct from framboids. They are nanoparticle clusters and are not produced by the same processes as those involved in framboid formation, nor do they behave in the same way. They are more akin to atomic clusters, which form similar constructs.