During the past ten years, nanotechnology has blossomed into an intricate field, connecting diverse areas of science such as medicine, electronics, and recently, cosmetology. Companies such as L'oreal are interested in using nanoparticles in makeup because they reflect light in such a way as to create unique pigments. Nanoparticles can be used in sunscreens because they deflect Ultra Violet rays and they can carry vitamins past the epithelial layer . However, there has been no systematic study of the cytotoxicity of nanoparticles. In this study we investigated whether nanoparticles are dangerous for dermal fibroblasts.

We chose to study how particle size and various concentrations of nanoparticles affect dermal fibroblasts. In order to create makeup and drug delivery systems which utilize "safe sizes", it is critical to discover what size is cytotoxic and how size affects cytotoxicity. We also investigated how various concentrations of nanoparticles affect fibroblasts. We experimented with two different sizes of citrate coated gold nanoparticles: 15 nm and 36.3 nm. Gold was used because it is inert and FDA approved, and citrate is present in the Krebs cycle to produce energy for cells. The nanoparticles were delivered to cells in solution at various concentrations: 0 ul/ml, 50ul/ml, 100ul/ml, 150ul/ml, and 200ul/ml.

Through taking confocal microscopy images of these cells, we showed that as the concentration of 15 nm particles increased, more nanoparticles accumulated within the cell. The accumulation of nanoparticles was lower when the cells were in 36.3 nm particle solutions, indicating that these larger particles could not easily enter the cells. Even though a particular makeup may have a low concentration of nanoparticles, if applied regularly, this minute concentration will accumulate within cells. Additionally, we found that the cell area (Fig 1, 2) and cell number were dramatically affected by the 15 nm particles, and so were the number of actin fibers in these cells. Knowing that the actin fibers, which create the cytoskeleton, and the extracellular matrix proteins regulate cell functions such as gene transcription, adhesion, proliferation, and differentiation (Alberts et al. 1994, 972) it is clear that nanoparticles can be dangerous for our health.

Further studies will include researching how palladium nanoparticles of different sizes affect cells, thus addressing the chemistry of nanoparticles, how nanoparticles in vitro can affect extracellular matrix proteins such as fibronectin, and the mechanisms by which nanoparticles enter cells.

This work was supported with funding from the Simons Foundation and the Garcia MRSEC program.