Colloidal Silver Nanoparticles from Ocimum sanctum: Synthesis, Separation and Their Implications on Pathogenic Microorganisms, Human Keratinocyte Cells, and Allium cepa Root Tips

In the present investigation, we report synthesis of anisotropic silver nanoparticles (AgNPs) from leaf extracts of medicinal herb Ocimum sanctum (Tulsi) and size/shape separation using facile sucrose density gradient centrifugation (SDGC). AgNPs were synthesized using aqueous Tulsi leaf extract with silver nitrate as a precursor. Spectral properties were studied using UV-Vis spectroscopy and morphological analysis, which showed that the synthesized AgNPs were anisotropic in nature; with size ranging from ca. 9-105 nm, was confirmed using Transmission Electron Microscopy (TEM). Conversion yield of AgNPs was calculated to be similar to 91.01% as confirmed by Inductively Coupled Plasmon Atomic Emission Spectroscopy (ICP-AES). The anisotropic AgNPs were further separated into silver nanorods, nanocuboids and nanospheres using SDGC. Surface functional moieties were studied using Fourier Transform Infrared Spectroscopy (FT-IR). AgNPs showed anti-microbial activity against highly pathogenic microorganisms like Sarcina lutea (gram positive) and Shigella sonnei (gram negative). Synthesized AgNPs also showed in vitro cytotoxic effect on human keratinocyte (HaCaT) cell line carried out using MTT-assay and IC50 obtained was 0.1 mu g/ml. In order to assess the environmental impact of synthesized AgNPs, we studied their effect on cellular mitotic event in Allium cepa root tips which revealed that the mitotic index considerably decreased upon treatment with AgNPs, thus questioning the impact of AgNPs dispense into the environment.