A range of particles and fibres (including single-walled carbon nanotubes (SWCNT), fullerenes (C₆₀), carbon black (CB), nC₆₀, and quantum dots (QD)) from nanotechnology have been studied in vitro to determine their toxicity in a number of cell types. In this study Monteiro-Riveiere et al. compared different in vitro tests of cell viability to investigate which was the most accurate one to examine toxicity of carbon (SWCNT, carbon black, fullerenes) and non carbon (quantum dots) nanomaterials. The viability of human epidermal keratinocytes (HEK) was assessed with calcein AM (CAM), Live/Dead (LD), Neutral red (NR), MTT, Celltiter 96® AQueous One (96 AQ), alamar Blue (aB), Celltiter-Blue® (CTB), CytoTox One™ (CTO), and flow cytometry. In addition, trypan blue (TB) was quantitated by light microscopy.

The quality of the assays was assessed by assay linearity (R2-value) with HEK cells plated on 96 well plates with concentrations from 0 to 25,000 cells per well. The results of the study show that TB, CAM and LD assays, which depend on direct staining of living and/or dead cells, were difficult to interpret due to physical interference of the NM with cells. Results of the dye-based assays varied a great deal, depending on the interactions of the dye/dye product with the carbon nanomaterials (CNM). Results show the optimal high throughput assay for use with carbon and noncarbon NM was 96 AQ. The authors conclude that CNM interact with assay markers to cause variable results with classical toxicology assays and may not be suitable for assessing nanoparticle cytotoxicity. They propose that more than one assay may be required when determining nanoparticle toxicity for risk assessment.

Inorganic nanoparticles (NPs) show great potential for medicinal therapy. However, biocompatibility studies are essential to determine if they are safe.

In this paper Diaz et al studied five different NPs, and they compared the cytotoxicity, internalization, aggregation in medium, and reactive oxygen species (ROS) production, using different tumoral and normal human blood cells.

The reported results mainly reveal that effects not only depend on the material used but equally on the cell type used. For instance, while all NPs are phagocytosed and induce ROS in mouse macrophages, they behave differently on human peripheral blood cells, both in respect to internalization and ROS induction.

Moreover, while in some instances the toxicity and ROS were positively correlated this could not be found in others.

Therefore differences depending on the cell type used are important and should be taken into account in standardizing the procedures for the evaluation of the toxicity (safety).

This paper is important because the physico-chemical characterization of the materials is often thought to be the main aspect in producing comparable data. The biological model, protocol, used is somewhat forgotten. This study underlines the importance of good biological characterization of toxicity studies.

Silica nanoparticles are produced on industrial scale serving as additives to cosmetics, drugs, printer toners, varnishes, and even food. In addition, nanosilicas are being developed for a host of biomedical and biotechnological applications such as cancer therapy, DNA transfection, drug delivery, and enzyme immobilization. The objective of this study is to assess the effects that monodisperse amorphous spherical silica particles of different size have on viability of endothelial cells.

The cytotoxicity was assessed with different methods: lactate dehydrogenase (LDH)-release and the MTT assay in the EAHY926 cell line.

Concentrations leading to 50% reduction of cells viability (TC₅₀) for the smallest particles tested (14, 15 and 16 nm diameter) ranging from 33 to 47 µg/cm² of cell culture, which is significantly different from values assessed for the “larger” nanosilica particles (TC50 ranging from 89 and 254 µg/cm² respectively for particles diameter of 19 and 60 nm). Fine silica particles (larger than 100 nm diameter) with diameter of 104 and 335 nm show very low cytotoxic compared to nanosized particles with TC₅₀ values higher than 1000 µg/cm².

Moreover, smaller particles also appear to affect the exposed cells faster, cell death (by necrosis and not apoptosis) being already observed within a few hours. It was calculated that the specific surface area of tested particles is an important parameter determining the toxicity of monodisperse amorphous silica nanoparticles.