Floral extracts-mediated green synthesis of NiO nanoparticles and their diverse pharmacological evaluations.

Biosynthesis has emerged as an exciting interface for assembling multifunctional metal oxide nanoparticles for diverse medicinal applications. Herein, biogenic nickel oxide (NiO-NPs) is synthesized by using floral extracts of Callistemon viminalis (C. viminalis) as a low cost, ecofriendly reducing and stabilizing agent. NiO-NPs were annealed at 300 °C, 400 °C and 500 °C while their physiochemical properties were established by HR-SEM/TEM, UV, XRD, FTIR, EDS, SAED and SQUID techniques. Particle size of NiO-NPs decreased with increase in annealing temperatures. Magnetization curves indicated superparamagnetic behavior of the biogenic NiO-NPs at 300 K. Highly crystalline NiO-NPs obtained after annealing at 500 °C were used for biomedical applications. The anti-leishmanial activity on Leishmania tropica promastigotes (KMH-23) and anticancer activity on HepG2 (RCB1648) revealed excellent inhibition potential with IC50 of 37.21 µg/mL and 47 µg/mL, respectively. Significant antibacterial effect was observed against Klebsiella pneumonia and Proteus vulgaris with MIC's of 12.5 µg/mL each. Acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and α-glucosidase inhibitory potential were comparable with positive control drugs. Moderate antioxidant activities were observed. NiO-NPs were observed to be hemolytic (30%) at higher dose (1000 µg/mL). Overall, NiO-NPs revealed a multifunctional nature that can be explored for diverse biomedical applications.Communicated by Ramaswamy H. Sarma.