Green synthesis of gold and silver nanoparticles using callus and fruit extract of Capsicum frutescens L. and their antimicrobial activity

Abstract Background: Capsicum frutescens L. is a species of chili pepper that is widely distributed and used as a spice and medicinal. In this study, green synthesis of gold and silver nanoparticles (AgNP and AuNP) were produced from the callus and fruit extract of C. frutescens L., and their antibacterial characteristics was investigated. In the present study ripened fruits seeds were used for in vitro proliferation of callus. 2,4- D and NAA+ BAP containing MS medium showed induction of callus, but proliferation was more when they subjected to grow in 2, 4-D containing medium. Calluses were of friable type. 0.15g of callus and dried fruits was used to synthesis of gold and silver nanoparticles synthesis. Results: Synthesised nanoparticles were confirmed by colour change, peak obtained in UV-Vis spectrum and scanning electron microscopy (SEM) characterisation. Synthesized AuNP- fruit exhibited spherical shape with size ranging from 44- 77nm, whereas AuNP- callus showed cubical shape with size ranging from 93- 152nm. Synthesized AgNP of both fruit and callus showed spherical shape size ranging from 73-75nm in callus whereas 95-250nm in fruit. Fourier transform infrared spectroscopy (FTIR) measurements were carried out to identify the possible biomolecules responsible for the capping and efficient stabilization of the gold and silver nanoparticles synthesized by the C. frutescens fruit and callus extract. More biomolecules were observed in AgNP- Fruit compared to AgNP- Callus, AuNP- fruit and callus. The antibacterial experiments were performed with two Gram positive and Gram negative bacteria, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, using the well diffusion method. The antibacterial properties of produced AuNP-fruit and callus of C. frutescens, where bacterial inhibition was similar between the two. The maximum zone of inhibition observed in AuNP was against Escherichia coli. Similarly, the maximum zone of inhibition was seen in AgNP-fruit against E. coli. Antifungal experiment was performed with Fusarium oxysporum, Cladosporium sphaerospermum and Botrytis cineria. The biosynthesized AgNP- fruit showed good results in inhibiting the growth of Fusarium oxysporum than the positive control. Conclusion: Both fruit and callus nanoparticles were more effective against bacterial strains. AuNP was not more effective against this strain compared to AgNP. This is the first report on nanoparticle synthesis using callus that showed the antimicrobial activities.