X-ray tomography shows the varying three-dimensional morphology of gold nanoaggregates in the cellular ultrastructure

Abstract

Soft X-ray tomography data were used for volume rendering of both cellular organelles and intracellular gold nanoparticle aggregates. They reveal variation in properties of the nanoaggregates with incubation time, cell type, and particle properties.

Intracellular optical probing with gold nanostars

“…Even though some single particles can be observed ( Figure 7A), the majority of the nanostars are part of agglomerates of sizes ranging between 100 and 450 nm (corresponding to ~10-1000 individual nanostars) without a particular spatial arrangement, in agreement with the strong SERS signals that were obtained from all the cells. These arrangements are similar to those found for spherical gold nanoparticles 37,38 that, unlike the linear arrangements of silver nanostructures, 70 Figure 7B and S7B), the distribution of particle accumulations is clearly different, with agglomerates larger in size (between 200 nm and 800 nm, corresponding to ~90-5700 individual nanostars) than those observed for 3T3 cells (Figure 7A and S7A). In the HCT-116 cells, there are also single particles distributed in the cytoplasm, indicating that the nanostructures are endocytosed as individual nanoparticles, similar to other gold nanostructures.…”

“…38,41 To study the nanostar-biomolecule interactions in the living cells, SERS spectra were obtained after incubation of cell cultures with gold nanostars for 24 h. After this incubation time, endolysosomes of many different maturation stages are known to form that are distributed across the cytoplasm. 37 The average spectra with the nanostars synthesized at different HEPES concentration differ ( Figure 5A-5C). To account for the known variability between individual spectra from the same cell culture batch that is expected due to (i) the biological variation, (ii) the particular local composition in the environment of the many different nanostars within each probed cell, and (iii) the variation that is inherent to each SERS experiment, 42,65 the occurrence of bands in each individual spectrum was analyzed regardless of their absolute or relative intensities ( Figure 5D-5F).…”

“…The formation of aggregates of the nanostars in cells is a very important aspect in their application, since, e.g., processing and endolysosomal fusion and maturation take place. 37 To obtain an idea on the impact of aggregate formation of the nanostars on the distribution of the local optical fields that are responsible for the electromagnetic enhancement in SERS, we performed 3D-FDTD calculations on simplified geometrical models of the nanostars. In Figure 4 the distribution of the intensity enhancement of an excitation field with respect to that of the incoming field at a wavelength of 785 nm, as used in the experiments here, is shown for nanostars with slightly different morphology.…”

“…We report here data on the distribution of gold nanostars in the cellular ultrastructure using 3D nanotomography together with detailed information from SERS on the structure and composition of the surface of nanostars residing in cells of two cell lines. Both cell lines, 3T3 and have been used in the past to study the uptake and processing of gold [36][37][38] or gold-composite 39,40 nanostructures. SERS can give information on the interaction of the molecules at the immediate surface of gold nanostructures and was recently shown to indicate details on the structure and interactions of and within the hard corona of plasmonic nanoparticles in living cells.…”

“…SERS can give information on the interaction of the molecules at the immediate surface of gold nanostructures and was recently shown to indicate details on the structure and interactions of and within the hard corona of plasmonic nanoparticles in living cells. 38,41 Adding the localization in the cellular ultrastructure by cryo soft X-ray nanotomography (cryo-SXT) of vitrified cell samples, a powerful tool to study the interaction of gold nanoparticles with the cellular ultrastructure and with each other, 37,38,42 we link the interactions at the gold nanostar surface to their fate inside the cells. Of the known surfactant-free synthesis routes, 11,[43][44][45] generation of the nanostars in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer for reducing, as capping agent and growth director is used here to ensure compatibility with the cell culture conditions.…”