High resolution SEM imaging of gold nanoparticles in cells and tissues

Abstract

The growing demand of gold nanoparticles in medical applications increases the need for simple and efficient characterization methods of the interaction between the nanoparticles and biological systems. Due to its nanometre resolution, modern scanning electron microscopy (SEM) offers straightforward visualization of metallic nanoparticles down to a few nanometre size, almost without any special preparation step. However, visualization of biological materials in SEM requires complicated preparation procedure, which is typically finished by metal coating needed to decrease charging artefacts and quick radiation damage of biomaterials in the course of SEM imaging. The finest conductive metal coating available is usually composed of a few nanometre size clusters, which are almost identical to the metal nanoparticles employed in medical applications. Therefore, SEM monitoring of metal nanoparticles within cells and tissues is incompatible with the conventional preparation methods. In this work, we show that charging artefacts related to non-conductive biological specimen can be successfully eliminated by placing the uncoated biological sample on a conductive substrate. By growing the cells on glass pre-coated with a chromium layer, we were able to observe the uptake of 10 nm gold nanoparticles inside uncoated and unstained macrophages and keratinocytes cells. Imaging in back scattered electrons allowed observation of gold nanoparticles located inside the cells, while imaging in secondary electron gave information on gold nanoparticles located on the surface of the cells. By mounting a skin cross-section on an improved conductive holder, consisting of a silicon substrate coated with copper, we were able to observe penetration of gold nanoparticles of only 5 nm size through the skin barrier in an uncoated skin tissue. The described method offers a convenient modification in preparation procedure for biological samples to be analyzed in SEM. The method provides high conductivity without application of surface coating and requires less time and a reduced use of toxic chemicals.

Mapping the Distribution of Particles in Hydrogel in Use for Nanoplasmonic Biosensors: A Comparison of Preparation Methods

“…The contrast of these features were however not significant enough for distinguishing them from artifacts associated to the sample preparations [63,64]. The contrast of NMNPs in gel-like samples may be improved by omitting the sample coating and by instead including highly conductive sample holders [65], or by using both SE and BSE detectors to obtain density dependent contrasts that highlights the high densities areas in the image [66]. Any hydrogel collapse may result in close packing of the GNRs.…”

“…The dimension of the contrast features in Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 26 April 2018 doi:10.20944/preprints201804.0335.v1 Figure 4a and 4c are comparable to the size of GNRs in Figure 4b, but difficult to quantize with respect to estimating the particle distributions. The contrast of NMNPs in gel-like samples may be improved by omitting the metal sample coating and by instead including highly conductive sample holders [65]. The detection of SE and BSE can also be combined to obtain density dependent contrasts that highlights the high densities areas in the image [66].…”

“…The small-contrast features in Figure 6a and 6c (shown with white arrows) are similar results to those in Figure 4a and 4c which could indicate the presence of GNRs since they are denser than the polymer network. As discussed for the results in Figure 4, these small-sized contrast features are difficult to quantize as a distribution of GNRs due to the low contrast intensity, but could be improved by using results from [65,66].…”

Wet chemical synthesis of quantum dots for medical applications

“…For Raman spectroscopy exfoliated ECs were incubated in AuNPs for 5 minutes. At the end of the procedure, 25 µl of the material were taken and placed on silicon wafers [21,22]. The wafers were placed in a preheated oven at 100° C for drying.…”

Penetration of spherical and rod-like gold nanoparticles into intact and barrier-disrupted human skin

“…photonics and nanoplasmonics including technological applications. In the field of life science it is important that small gold nanoparticles can be probed in biological matter, as has been reported for electron microscopy approaches [2]. Complementary to electron microscopy is X-ray microscopy, which combines high spatial resolution with chemical selectivity, which was recently reviewed by Lawrence et al [3].…”