## 1 Introduction  
Nanoparticles are particles with dimensions in the \(10^{-9}\) m range that possess special physico-chemical properties. These unique characteristics have recently led to increased attention regarding the research carried out on nanoparticles, as well as to the development of nanotechnology as an interdisciplinary field. Nanotechnology has applicability in many fields, being of great interest in medicine, pharmaceutical and cosmetics industries, energy, agriculture, environment, and food industry [1, 2]. Silver nanoparticles (AgNPs), in particular, are known to have remarkable optical, electrical and antimicrobial properties. These properties can be correlated with the small particle size, and make it possible for AgNPs to be used in biosensors, composite fibers, superconducting materials, medical imaging, medicines, and cosmetics [3]. Out of all biological properties, the antibacterial action is probably the most studied, as it offers new pharmacotherapeutic perspectives in the context of the rising resistance of pathogenic bacteria to classical antimicrobial agents [4]. Moreover, particularly important are the antioxidant and cytotoxic activities, that were more recently discovered for such materials, but are, nonetheless, more and more studied by researchers in the field [5; 6]. The current study focuses on the importance of green chemistry in the synthesis of nanoparticles. Traditional physical and chemical methods are less and less used because they use toxic chemicals, require a large amount of energy, have high processing costs and generate nanoparticles with relatively low stability given their aggregation tendency [7]. Biological synthesis methods offer many advantages, which is why they are used preferentially instead of classical methods [8]. The main advantage is represented by the use of natural agents for the synthesis, stabilization and control of the shape, size and distribution of nanoparticles. The present paper investigates the synthesis of silver nanoparticles using green chemistry and their characterization. For the synthesis of nanoparticles using biological methods, we chose _Tagetes erecta_ (_T. erecta_), an ornamental plant very common in most geographical areas, taking into consideration its availability, as well as the fact that the species has been intensively studied regarding its chemical composition [9]. The species is a popular plant found in the Asteraceae family and it is widely cultivated for its decorative properties, as well as for the extraction of carotenoids [9; 10]. It has been used since ancient times in traditional medicine, especially in Mexico and South America, to treat a wide variety of diseases and conditions. Moreover, the flowers of _T. erecta_ are also found in the pages of the Mexican Pharmacopoeia [11]. In Mexico, the whole plant was used to make an infusion or a decoction in case of odds and respiratory disorders, but also to be used as a stimulant or as a muscle relaxant. Pressed juice or leaves were used as aphrodisiacs, diaphoretics, emetics, or for the treatment of liver disease or menstrual disorders. An ointment made from squeezing juice or leaves was applied externally in the treatment of malaria, to prevent the installation of chills. In Brazil, the infusion of the plant was intended for cases of bronchitis, cold, or rheumat, while the infusion obtained from the roots was used as a laxative. In India, the juice obtained from flowers was administered internally to \"purify\" the blood, and the juice obtained from the whole plant was used as ear drops or as treatment for eye infections [11; 12]. In the traditional medicine of various countries, it is believed that the flowers of the species can treat various skin infections, such as those that occur in case of wounds, burns, ulcers, eczema, or other dermatological conditions. The plant has also been used for kidney diseases, muscle or ear pain, or for the treatment of abscesses [13]. Taking into account the diversity of chemical compounds found in _T.