Abstract
Zinc oxide nanoparticles were synthesized using the aqueous leaf extracts of Plectranthus barbatus (Plb-ZnO NPs) and characterized by UV visible spectroscopy, XRD, FUR, SEM and EDS. UV Visible spectra recorded the absorbance peak of Plb-ZnO NPs at 343 nm. SEM analyses showed the spherical shape of Plb-ZnO NPs with the particle size between 30 and 60 nm. Plb-ZnO NPs exhibited antibacterial and antibiofilm activity against Gram positive Bacillus subtilis at all tested concentrations. In contrast, Plb-ZnO NPs showed antibacterial and antibiofilm activity against Gram negative Vibrio parahaemolyticus and Proteus vulgaris only at 100 mu g/ml. The Atomic absorption spectrometry (AAS) revealed that Zn2+ dissolution was 1.87 and 8.8 mu g/L at 10 and 160 mu g/L of Plb-ZnO NPs respectively. The body accumulation of Zn2+ was increased from 0.8 mu g/g body weight to 3.5 mu g/g body weight when C. cornuta exposed to 10 mu g/L and 160 mu g/L. respectively. Plb-ZnO NPs were toxic to Ceriodaphnia cornuta neonates (LC50: 28 mu g/L). Plb-ZnO NPs caused 100% mortality of C cornuta at 160 mu g/L after 24 h. However, zinc acetate does not cause any mortality of C cornuta upto 350 mu g/L. The light and confocal laser scanning microscopic images evidenced the uptake and accumulation of Plb-ZnO NPs on the internal gut regions of C cornuta at 160 mu g/L after 5, 10, 15, 20 and 24 h. Abnormalities in the swimming behaviour such as erratic swimming (ERR), migration to bottom (BOT) and migration to water surface (SUR) of C cornuta were noticed after treatment with different concentrations of Plb-ZnO NPs. (C) 2017 Elsevier Ltd. All rights reserved.