Melatonin improves bioreductant capacity and silver nanoparticles synthesis using Catharanthus roseus leaves

Melatonin is a natural hormone found in a variety of living organisms, including plants, and possesses the potential to act as a growth promoter and stress alleviator. The present study aims in understanding the effect of melatonin in Catharanthus roseus (C. roseus; medicinal plant used in anticancer therapy) leaf extracts for enhanced silver nanoparticle synthesis. Our results indicated that the supplementation of 300 μM melatonin to C. roseus leaves improves silver nanoparticles (AgNPs) synthesis. The phytosynthesized AgNPs were characterized using UV-Vis spectroscopy, FE-TEM, Zetasizer, XRD, AAS and FTIR spectroscopy. Moreover, the AgNPs were found to be smaller in size (ranging from 10–25 nm) with potent antibacterial activity (MIC and MBC values against the most prevalent urinary tract pathogens, Escherichia coli and Staphylococcus aureus, being 15.6 ± 0.0 μg mL−1 and 31.25 ± 0.0 μg mL−1 respectively). Furthermore, LC-MS/MS analysis of the melatonin treated C. roseus leaf extracts indicated the presence of significant biomolecules; 6-acetyl morphine (used as an analgesic), rauwolscine and fisetin (anticancer compounds). Melatonin treatment of C. roseus leaves also enhanced its antioxidant potential and total chlorophyll content. Thus, melatonin serves as a potential agent to improve C. roseus growth and therapeutic potential.