Introduction: According to the National Nanotechnology Initiative (NNI) definition, nanoparticles are structures with sizes from 1-100 nm in at least one dimension. There are different types of nanoparticles and each one has an exclusive set of properties and applications and can be synthesized by conventional or unconventional methods.
Synthesis of nanoparticles can be done physically, chemically and green. Green synthesis produces stable nanoparticles that are environmentally friendly and economically viable. The growing popularity of green methods has led to the synthesis of nanoparticles using different sources such as plants, algae, microorganisms (bacteria, fungi, etc.), which has led to production on a larger scale with less pollution for the environment and human health.
Silver and gold nanoparticles are considered noble metal nanoparticles (i.e. metals resistant to corrosion and oxidation). These metal nanoparticles have characteristics such as: high electrical and thermal conductivity, chemical stability, antimicrobial activity against a wide range of microorganisms. .
In the green synthesis of nanoparticles, including gold and silver, unlike microorganisms, plants are completely used, that is, nanoparticles can be synthesized by using leaves, stems, flowers, seeds, roots, fruits, skins and latex of plants. Microorganisms such as fungi, bacteria, yeasts are of great interest for the synthesis of nanoparticles, but this process is threatened by culture contamination, long methods and less control over the size of nanoparticles.
Gold and silver nanoparticles synthesized in a green way have a wide range of properties, including antibacterial, antifungal, antiviral, etc., and are widely used in the field of biomedicine, including cancer diagnosis and treatment, drug delivery, nanosensors, and biomarkers.
Due to the great importance of green synthesis, in this article we have reviewed the recent methods of green synthesis of gold and silver nanoparticles.
Methods: Google scholar database was used to prepare this review article. 29 limited articles from 2019 to 2023 have been used with the aim of investigating the green synthesis of gold and silver nanoparticles and their biological applications. The key phrases used are respectively green synthesis of silver/gold nanoparticles by
Results: Each of the gold and silver nanoparticles synthesized by biological methods have a specific size and shape. The morphology (size and shape) of nanoparticles is determined by the reaction conditions so that they may have different shapes such as triangular, spherical, hexagonal, polyhedral, etc.
Synthesized nanoparticles are analyzed using various techniques including UV-vis spectroscopy, FTIR, XRD, TEM, EDX, AFM, SPR, X-ray diffraction, etc. to confirm their characteristics as a nanoparticle.
We arranged the information related to the comparison of gold and silver nanoparticle synthesis methods as well as the use of each in separate tables.
Conclusion: Green synthesis of gold and silver nanoparticles by bacteria or using natural extracts as biologically prepared reagents shows high solubility, performance and stability in the synthesized nanoparticles. The use of organisms or reagents of biological origin is considered one of the most promising methods because its cost is low, diverse natural resources are used, and it also helps to reduce the potential toxicity of nanoparticles. Metal nanoparticles such as gold are widely used as nanomaterials in cancer treatment, biomolecular screening, selective destruction of certain cells, etc., as well as silver nanoparticles with wide applications in drug delivery, nanomedicine, cosmetics, food industry and agriculture.
It is suggested that in the future the green synthesis of these two nanoparticles will be done using other natural and biological materials and the characteristics of the methods will be compared.
Keywords: Green synthesis, gold nanoparticles, silver nanoparticles, microorganisms, plants