Nanoparticles from various materials can be prepared by relatively simple methods. During the past few decades, a variety of different methods have been reported and reviewed for synthesizing gold colloids of monodisperse and uniform sized particles. In present investigation, a new method of one-pot biosynthesizing of gold nanoparticles (GNPs), using geranium leaves extract as a reductant and stabilizer is reported. GNPs were characterized by UV-visible spectroscopy; transmission electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectroscopy (FTIR). The cytotoxicity of the GNPs was evaluated using the 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) method against SUDHL-4 cell line. The transmission electron microscopy results indicated that the GNPs were spherical in structure and almost 20 nm in diameter. Ultraviolet visible spectroscopy exhibited an absorption peak at 545 nm. The GNPs exhibited high crystallinity, with the (111) plane as the predominant orientation, clarified by X-ray powder diffraction. Toxicological assays of as-prepared GNPs revealed that the green GNPs were nontoxic. These biogenetic GNPs have great potential biomedical application for ultrasensitive detection of biomarkers. Keywords: Green synthesis, cytotoxicity, gold nanoparticles (GNPs), geranium (Pelargonium graveolens L.), SUDHL-4 cell line
