Green synthesis of silver nanoparticles by using Ocimum sanctum and unveiling their antibacterial and antifungal properties

Background : The rise of multidrug-resistant bacteria requires the search for new antimicrobials. AgNPs are recognized as emerging antimicrobial agents, however, commonly used methods for the synthesis of AgNPs utilize noxious chemicals. In green synthesis of AgNPs with Ocimum sanctum (Green and Black Tulsi), plant-derived phytochemicals act as natural reducing and stabilizing agents and represent an eco-friendly medium. Method : The leaf extracts of dried and fresh Green and Black Tulsi were prepared in aqueous condition, and employed for the synthesis of AgNPs, using silver nitrate solution. The synthesis was confirmed by color change and was characterized using UV–Vis spectroscopy (for nanoparticle formation), FTIR (for analysis of functional group involved in reducing and stabilizing of nanoparticles) and FESEM (morphological, size analysis). Antibacterial activity was determined against multidrug resistant bacteria (ESKAPE pathogens) by Minimum Inhibitory Concentration (MIC) assay while antifungal activity was tested against Aspergillus niger through agar well diffusion. Results : The UV-Vis absorption peak around 400 nm observed for the prepared AgNPs indicates their formation. FTIR investigation revealed the existence of the functional groups of OH and carbonyl, which are mainly responsible for the reducing of Ag+ ions. Non-uniform morphology with particle size between 100–200 nm was observed under FESEM images. The antifungal activity against Aspergillus niger showed a clear zone of inhibition of 18 mm, indicating strong antifungal efficacy.​The Minimum Inhibitory Concentration (MIC) values for the nanoparticles were 0.5 µg/mL and 16 µg/mL against E. coli ATCC 25922 and S. aureus ATCC 29213, respectively, with MIC ranges of 1–4 µg/mL for clinical isolates. Conclusion : Green synthesized AgNPs employing Tulsi extracts is a cost effective, eco-friendly and scalable method producing the AgNPs with enhanced antimicrobial activity. This is an approach to combining the therapeutic efficacy of Tulsi and Nanotechnology. The synthesis of nano particles from Tulsi could prove beneficial for development of alternate strategies in anti-bacterial and antifungal activities.