Nanoparticles (NPs) have opened a new horizon in the field of medicine delivery, gene delivery, nanomedicine, and biosensing in the 21st century [1, 2]. NPs are also applicable in environmental protection, sensing, communication, cosmetics, medical industry, etc. [3]. The magnetic and catalytic properties of NPs, along with their improved surface-to-volume ratio, can be enhanced by some unique modified processes [4, 5]. NPs can be synthesized by using an array of physical, chemical and biological methods. The hydrothermal processes, physical vapor deposition, microemulsion, precipitation, ultrasonic irradiation, chemical reduction, plasma, and sol–gel methods are the best example of the above methods [6]. These methods required a variety of hazardous chemicals, and a huge amount of energy to synthesize the NPs. The above methods also utilized a very high temperature and pressure which is very harmful to the environment. Accordingly, the product cast is very high due to the higher order of the equipment used in these methods [7]. As a result, an environmentally friendly method is required to synthesize the NPs without utilizing any toxic components. Recently, many scholars are taking interest to prepared the NPs via herbal rout. In medical science, especially in diagnosis and treatment of various decease the biological method of the synthesis of NPs is comparatively more advantageous than the physical/chemical methods. Thus, the biological method has replaced the physical and chemical method for the synthesis of NPs due to the high energy consumption, low cost, environmental impact and production of more stable and biocompatible NPs [8, 9]. Microorganisms [10], enzymes [11], fungi [12], and plant extracts [13] are used to manufacture metal and metal oxide NPs by green route. Nevertheless, it is challenging to develop effective environmentally friendly methods to generate NPs with absolute size, shape, and composition. Nontoxic and environmentally friendly NPs are prepared by a variable phytochemistry-based process using biological entities [14, 15].
ZnO NPs are one of the cost-effective metal oxide NPs with minimal toxicity and highest biocompatibility, which are used in photothermal therapy, antibacterial and anticancer drug distribution, cell imaging, and biosensing, making them a promising tool in the field of biomedical sciences [16, 17]. Various synthesis techniques for NPs improve both the crystal size and their properties [18]. Phyto-synthesis is widely accepted due to its nontoxicity, environmental friendliness, and wide range of applications such as antimicrobial properties, antioxidants, anti-aging, anticancer, and so on. In the phyto-synthesis method, secondary metabolites trap the metal ions and act as capping agents that help stabilize the NPs in terms of electrostatic, steric, hydration forces, depletion, and Vander-Waals forces [19, 20]. The interactions of ZnO NPs with microbial cells are possible due to the smaller surface area and higher charge density of ZnO NPs [21, 22]. The Calendula officinalis L. is a flowering plant which belongs to the family Asteraceaeis. A wide rage of pharmacological effects can be observed in the extract of Calendua officinalis L. [23] due to which it can be unitilized as antiseptic, stimulant, diaphoretic, antispasmodic and anti-pyretic agents [24, 25]. It has been observed that the leaf extracts of the calendula officinalis have anti-cancerous, antiviral anti-genotoxic, anti-oxidant, anti-microbial and anti-inflammatory properties [26, 27].
The present study focuses on the synthesis of ZnO NPs via the green route using Calendula officinalis L. The prepared ZnO NPs were characterized by XRD, FE-SEM, UV-Vis and FT-IR spectroscopy for the size, shape, optical properties and stability of the ZnO NPs.