Phytogenic nanoparticles: synthesis, characterization, and their roles in physiology and biochemistry of plants

Researchers are swarming to nanotechnology because of its potentially game-changing applications in medicine, pharmaceuticals, and agriculture. This fast-growing, cutting-edge technology is trying different approaches for synthesizing nanoparticles of specific sizes and shapes. Nanoparticles (NPs) have been successfully synthesized using physical and chemical processes; there is an urgent demand to establish environmentally acceptable and sustainable ways for their synthesis. The green approach of nanoparticle synthesis has emerged as a simple, economical, sustainable, and eco-friendly method. In particular, phytoassisted plant extract synthesis is easy, reliable, and expeditious. Diverse phytochemicals present in the extract of various plant organs such as root, leaf, and flower are used as a source of reducing as well as stabilizing agents during production. Green synthesis is based on principles like prevention/minimization of waste, reduction of derivatives/pollution, and the use of safer (or non-toxic) solvent/auxiliaries as well as renewable feedstock. Being free of harsh operating conditions (high temperature and pressure), hazardous chemicals and the addition of external stabilizing or capping agents makes the nanoparticles produced using green synthesis methods particularly desirable. Different metallic nanomaterials are produced using phytoassisted synthesis methods, such as silver, zinc, gold, copper, titanium, magnesium, and silicon. Due to significant differences in physical and chemical properties between nanoparticles and their micro/macro counterparts, their characterization becomes essential. Various microscopic and spectroscopic techniques have been employed for conformational details of nanoparticles, like shape, size, dispersity, homogeneity, surface structure, and inter-particle interactions. UV-visible spectroscopy is used to examine the optical properties of NPs in solution. XRD analysis confirms the purity and phase of NPs and provides information about crystal size and symmetry. AFM, SEM, and TEM are employed for analyzing the morphological structure and particle size of NPs. The nature and kind of functional groups or bioactive compounds that might account for the reduction and stabilization of NPs are detected by FTIR analysis. The elemental composition of synthesized NPs is determined using EDS analysis. Nanoparticles synthesized by green methods have broad applications and serve as antibacterial and antifungal agents. Various metal and metal oxide NPs such as Silver (Ag), copper (Cu), gold (Au), silicon dioxide (SiO2), zinc oxide (ZnO), titanium dioxide (TiO2), copper oxide (CuO), etc. have been proven to have a positive effect on plant growth and development. They play a potentially important role in the germination of seeds, plant growth, flowering, photosynthesis, and plant yield. The present review highlights the pathways of phytosynthesis of nanoparticles, various techniques used for their characterization, and their possible roles in the physiology of plants.