Figure 4.

Experimental evaluation of cytotoxicity of polymer-coated CdSe nanoparticles. Toxicity to NIH-3T3 fibroblasts of a NC-containing solution was estimated after 48-hour application. Dose-response curve for cell viability was measured with a Resazurin assay [74]. Reazurin is a nonfluorescent dye that is metabolized in functional mitochondria and converted into resorufin which fluoresces red. Black and grey curves show two experiments (n = 8 measurements each). Normalized survival R(c) after application of a Cd²⁺ concentrationc(Cd) was estimated from the change in absorbance of the converted dye measured at 600 nm. Changes in R became significant at c (Cd) around 3–5 μM, whereby c (Cd) refers to the concentration of Cd²⁺ on the surface of the CdSe nanoparticles, which accounts for the different toxicity of different-size NCs. This concentration of Cd²⁺ corresponds to a concentration of CdSe nanoparticles of 50-70 nm. Similar data was obtained with a cell adhesion assay [71] (not shown). In contrast for free cobalt ions (Co²⁺), cytotoxic effects became significant at around 50 $\mu$M (data not shown).