Biosynthesis, characterization, and antibacterial activity of zinc oxide nanoparticles derived from Bauhinia tomentosa leaf extract

The combination of nanotechnology and biological science has been created a new path for the researchers to exploit in various biological fields. Nowadays, synthesis of metal nanoparticles becomes growing attention in nanotechnology research due to its tremendous applications in medicine, biomedical, pharmaceutical, drug delivery, and photocatalytic activity [ 1 ]. In the past few decades, there is an increased demand for the metallic nanoparticles which can be synthesized by various traditional physical and chemical methods in different shapes and sizes. Irradiation [ 2 ], microwave processing [ 3 ], solvothermal [ 4 ], and ultrasound processing [ 5 ] are some of the physical approaches for the metallic nanoparticle synthesis. The disadvantages of physical method involve the processing done at elevated temperature and pressure, requires large space to set the machines and also the cost is high [ 6 ]. On the other hand, utilization of hazardous substances such as reducing agents, organic solvents, and stabilizers in chemical approach causes hazardous for the labourers as well as environment during synthesis. It has been reported that the toxic substances reside inside the nanoparticles if it is prepared either physical or chemical method induces hazard in the field of their applications [ 7 ]. The alternative method to synthesize nanoparticles in an eco-friendly, biocompatible, safe, and cost-effective is green approach, which allows large-scale production of nanoparticles through bacteria, fungi, algae, and plants. Different plant parts such as root, stem, leaf, flowers, and fruits are rich in phytochemical substances and act as a stabilizing and reducing agent in the production of nanoparticles [ 8 , 9 , 10 ]. Among all other metal nanoparticles, ZnO nanoparticles possess tremendous applications in medical field such as UV filtering in preparation of sunscreen lotions, anti-inflammatory, wound-healing, anti-cancer, antifungal, antibacterial, and targeted drug delivery [ 11 , 12 ]. ZnO NPs can be produced in different nanoscale sizes and structures in the form of flakes, flowers, belts, rods, and wires [ 13 ], thereby employed flexibly in heavy metal removal and biomedical applications.