Choosing safe dispersing media for C60 fullerenes by using cytotoxicity tests on the bacterium Escherichia coli

Assessment of C(60) nanotoxicity requires a variety of strategies for dispersing it into biological systems. Our objective was to determine organic solvent/surfactant combinations suitable for this purpose. We used Escherichia coli (ATCC# 25254) to determine the cytotoxicity of C(60) in solvents at concentrations up to 100 ppm. In this preliminary study we hypothesized that C(60) toxicity is directly correlated with its degree of dispersion in solution and that more solubilizing solvents induce higher toxicity. Test solvent concentration (1%) and Tween 80 (0.04%) were based on E. coli viability assay. Sonication was used to further enhance C(60) dispersal. The end-point response was measured with viability (in terms of LC(50)) and general metabolic activity (in terms of IC(50)) of E. coli cultures after exposure. The ultimate goal was to select safe dispersing media and enrich the database of C(60) nanotoxicity for NanoQuantitative-Structure-Activity-Relationship (NanoQSAR) applications. LC(50) range was 30 ppm to >400 ppm. IC(50) followed the trend. Among the six solvent combinations, DMSO combined with Tween 80 was the optimum combination for defining a dose-response relationship for assessing its toxicity to E. coli. However, N,N-dimethylformamide has the greatest potential to be a safe solvent for C(60) applications based upon its biocompatibility. Solvent solubility alone could not account for the cytotoxicity observed in this study.