Introduction: One of the major aspects of nanotechnology science is concerned with the production and development of toxicity–free synthesis of metal nanoparticles. Plant extracts have proven to be non-toxic to living organisms, a reproducible resource and environmental friendly material containing polyphenols [1]. A class of compounds known as diterpenes, or flavonoids are poly-phenolic which receiving increasing attention for a variety of health promoting properties.One agent in particular is carnosol(one of the major fraction in rosemary extract) which has been reported to have broad anti-cancer properties in several cell line models including prostate, breast, leukemia as well as others [2]The aim of this study is, synthesis of iron nano-particles using Rosmary officinalis extract and evaluation of cytotoxic effects of this nanoparticles . Synthesis, Characterization and application of zero valent (Fe NPs) For prepared extract dry rosemary leaves was boiling in de-ionized water with a concentration of 60.0 g/Lat 80 °C for 1 h and vacuum-filtered. EL-Fe NPs were synthesized by adding the extract to 0.10 M FeSO4 at a volume ratio of 2:1 at room temperature. The immediate appearance of black color indicated the reduction of Fe2+ ions.[3] The average particle size of nanoparticles was estimated to be 50 nm. The formation of nanoparticles as well as their morphological dimensions in the TEM study revealed that the particles were aggregated, and showed that the nanoparticles size was below 20 nm . FTIR indicated that some polyphenols are bound to the surfaces of EL-Fe NPs as a capping/stabilizing agent was used to detect EL-Fe NPs as well The potential cytotoxic and anti-proliferative activities of nanoparticles were evaluated on using MTT Assay. Concentrations needed for half-maximal inhibition (IC50s) were calculated using CalcuSyn software. The results showed that the cytotoxic effects of this iron green nanoparticles on viability of 4T1 breast cancer cells was 35 times more than NIH3T3 normal cells (IC50 5.58 ± 2.25 ug/ml for 4T1 compared with 196.8 ± 16.02 ug/ml for NIH3T3 normal cells. The anti-cancer properties of rosemary extract is attributed to the Both carnosol and carnosic acid. conclusion: The results of this research indicated that secondary metabolites present in the rosemary extract could be a source of natural products with antiproliferative activity to be used against cancer.

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