Green Synthesis of Nickel Oxide (NiO) Nanoparticles Using Neem (Azadirachta indica) Leaf Extract: Physicochemical Characterization and In Vitro Antidiabetic, Antioxidant, and Antimicrobial Activities

Abstract

X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy
(SEM combined with energy dispersive X-ray spectroscopy or EDX) were used to characterize
the biosynthesized NiO-Neem nanoparticles using the aqueous leaf extract of neem (Azadirachta
indica) as a reducing and capping agent. A face centred cubic (bunsenite) NiO lattice with the
space group Fm-3m was found to be phase pure, having an average crystallite size of about 6.4
nm (Debye-Scherrer method) and 7.8 nm (Williamson-Hall analysis), and a very small tensile
microstrain (~5.1 x 10-4). FTIR spectra indicated the presence of the diagnostic Ni-O stretching
doublet near 588 cm-1 and 409 cm-1, and also the presence of bands due to the presence of traces
of neem phytoconstituents while SEM-EDX analysis suggested the presence of a surface layer
of oxygen with the oxygen to Ni ratio of approximately 2:1, indicating that the Ni metal particles
had an oxygen rich surface constitution. In the in vitro bioactivity assays, NiO-Neem
nanoparticles were most potent antidiabetic (inhibiting α-glucosidase, IC50 14.51 +/- 0.14
microg/mL and inhibiting about 38-fold better than acarbose) and the most potent antioxidant
sample (DPPH radical scavenging ability, IC50 95.24 +/- 0.02 microg/mL). By the agar well
diffusion method, organism dependent detection of activity was observed wherein NiO-Neem
showed dose dependent activity with a resistance seen for Escherichia coli and Staphylococcus
aureus. The present study shows, through the green synthesis using the Plant parts of neem, the
synthesis of NiO nanoparticles of uniform size, optimum parameters and optimum concentration
of phytochemical coating which exhibited significant biomedical activity (antidiabetic,
antioxidant) with desirable organ and application specificity.