Research Article Maha Daghestani, Sarah A. Al Rashed, Wadha Bukhari, Badryah Al-Ojayan, Eiman M. Ibrahim, Asma M. Al-Qahtani, Nada M. Merghani, Rasha Ramadan, and Ramesa Shafi Bhat* Bactericidal and cytotoxic properties of green synthesized nanosilver using Rosmarinus officinalis leaves https://doi.org/10.1515/gps-2020-0025 received November 12, 2019; accepted February 04, 2020 Abstract: Green synthesized nanoparticles from plant extracts are being used in various biomedical applications, particularly because of their bactericidal and cytotoxic activities. In this study, silver nanoparticles (AgNPs) were successfully synthesized from the Rosmarinus officinalis aqueous leaf extract. Di fferent spectroscopic and microscopic analyses such as ultraviolet - visible (UV-vis) spectroscopy, Fourier transform infrared spectroscopy ( FTIR) , scanning electron microscopy, and energy- dispersive X-ray spectro- scopy were performed to verify the biosynthesized AgNPs in our sample. The formation of nanosilver particles was preliminarily confirmed by UV- vis spectroscopy at 400 nm. The presence of carboxylic or amide groups was confirmed by FTIR, for the reduction of the silver ion. Transmission electron microscopy confirmed a particle size of 12–22 nm. The prepared AgNPs showed good antibacterial activity against human pathogens and good cytotoxic activity against the human breast cancer cell line ( MDA MB 231) . The nanoparticles prepared from R. officinalis can be used for various biomedical applications. Keywords: Rosmarinus officinalis, green synthesis, nanosilver List of abbreviations AgNPs Silver nanoparticles DLS Dynamic light scattering EDX energy-dispersive X-ray spectrum FTIR Fourier transform infrared spectroscopy PDI Polydispersity index SPR Surface plasmon resonance TEM Transmission electron microscopy UV-vis Ultraviolet-visible absorption 1 Introduction Silver has been used by mankind for a long time because of its low toxicity and good biocidal properties. It is frequently used in water-purifying systems in hospitals, for healing injuries, and in the field of nanoparticle synthesis [1]. Some bacteria are resistant to silver and are able to accumulate this metal up to 25% of their dry weight biomass in their cells [2], which makes them suitable for extracting silver from ores [3]. Silver nanoparticles (AgNPs) are used as an effective nano- drug against many diseases [4]. Also, they are more efficient in killing silver-resistant bacteria due to their highly developed surface area [5], whereas highly reactive silver ions (Ag + ions) form insoluble precipitates so are less efficient in killing bacteria [6]. Nanobiotechnology is constantly exploring the synthesis of metal nanoparticles in a nontoxic and ecofriendly manner [7]. The main requirements for the synthesis of a metal nanoparticle are the solvent medium, a reducing agent, and a nontoxic stabilizer of nanoparticles [8]. Plants are rich in active compounds and, thus, can be used as a good source of reducing agents for synthesizing nanoparticles [9]; this has Maha Daghestani: Zoology Department, Science College, King Saud University, Riyadh, Saudi Arabia; Central Laboratory, Female Center for Medical Studies and Scientific Section, King Saud University, Riyadh, KSA, Saudi Arabia Sarah A. Al Rashed: Department of Botany and Microbiology, College of Science, King Saud University, Riyadh, Saudi Arabia Wadha Bukhari, Badryah Al-Ojayan, Eiman M. Ibrahim, Asma M. Al-Qahtani, Nada M. Merghani, Rasha Ramadan: Central Laboratory, Female Center for Medical Studies and Scientific Section, King Saud University, Riyadh, KSA, Saudi Arabia  * Corresponding author: Ramesa Shafi Bhat, Biochemistry Department, College of Science, King Saud University, Riyadh, Saudi Arabia, e-mail: rbhat@ksu.edu.sa Green Processing and Synthesis 2020; 9: 230–236 Open Access. © 2020 Maha Daghestani et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License.