Shape and size of non-spherical silver nanoparticles: implications for calculating nanoparticle number concentrations

Abstract

The international drive to measure accurate number concentrations of nanoparticles is impeded by the typically heterogeneous populations of non-spherical nanoparticles. The irregular shape and size of "50 nm" silver nanoparticles is studied using Electron Tomography. It is evidenced that even for highly symmetrical particles the volume can be over 20% less than that of the circumscribed sphere; more irregularly shaped particles can have volumes of over 45% less. On this basis, criteria are provided to determine the particle sphericity from 2D projections obtained from Electron Microscopy, including an empirical method for particle volume estimation. The results allow the visualisation of irregularly shaped particles, revealing the presence of previously unseen voids in the nanoparticle structure. Comparison of tomographic data with other commonly used particle-sizing methods exposes the limitations of these methods in studying nanoparticle populations that exhibit heterogeneity.

Effect of surface pinning on magnetic nanostuctures

“…Like other nanomaterials [50], the surface morphology or shape of a core-shell nanocomposites may be changed. Morphology of the nanoparticle can be spherical [51], squre [49], elliptical [52], triangular [53] or it may be irregular [54]. Their magnetic properties depend crucially on the surface anisotropy [55].…”

Silver Nanoparticle Detection in Real-World Environments via Particle Impact Electrochemistry

“…These oxidation kinetics in real-world potable water samples -in contrast to the case in which nanoparticle dissolution is studied in de-ionised water 18 -are variable and can be highly sensitive to the presence of trace ions. That said the above demonstrates that by 'overestimated' in the TEM analysis 8 or b) the presence of the citrate causes a size sensitivity leading to the probability of experimentally observing larger particles being partially being reduced. As can be seen in SI section 3 the presence of the citrate reduces the observed nanoimpact frequency and furthermore nano-impact experiments are known to be sensitive to the presence of organics.…”

“…Light scattering techniques enable nanoparticles to be studied under conditions that more authentically reflect the real world environment; however, these methodologies too are not without their limitations, for example, Dynamic Light Scattering (DLS) are commonly limited to relatively monodisperse samples [10][11] and nanoparticle tracking analysis (NTA) fails for particles smaller than ca 25nm. 8 Moreover, for plasmonic nanoparticles such as those fabricated from silver and gold, the agglomeration level of the material may be monitored optically by studying the shift in the adsorption wave, providing a sensing platform for the detection of metal ions. [12][13] As one of the most commonly used nanoparticles, a considerable quantity of nano-silver has been accumulated in water, soil, plants and animals in the food chain.…”

Electrochemical impacts complement light scattering techniques for in situ nanoparticle sizing

“…diameter distribution, the impact data is first windowed to statistically reveal authentic numbers of spikes, 15 and then weighted for diffusion to eliminate the effect of unequal probabilities of detecting the particles owing to their size-dependent mobility (See SI Section S3). 22 As a result, 443 ('20 nm') and 932 ('30 nm') spikes were confirmed as single features and the windowed-and weighted-diameter distributions were depicted in the Figure 2 with measured diameters in Table 1.…”

“…To obtain true volumes, electron tomography is required. 15 DLS and NTA techniques quantifying particulate diffusional movements in bulk are only able to measure hydrodynamic radii based on the Stoke-Einstein law assuming equivalent diffusing perfect spheres. They are unable to provide any related shape information.…”