Biocompatibility and ecotoxicity concerns associated with chemically produced metallic nanoparticles have led to an increasing interest in the development of environmentally benign alternatives for nanoparticle synthesis using biological platforms. Herein, we report the utilization of an extract of seed-derived callus of Catharanthus roseus for the production of stable silver nanoparticles (Ag NPs). The bioreduction of silver ions was evident from UV-Vis spectroscopy results: the absorption maxima were observed at 425 nm, indicative of elemental silver. Transmission electron micrographs revealed that the Ag NPs were well-dispersed and predominantly spherical with particle sizes in the range of 2-15 nm. The synthesized Ag NPs exhibited colloidal stability in an aqueous dispersion for a period of 120 days, as indicated by UV-Vis absorbance spectra and zeta potential measurements. Fourier transform infrared spectroscopy revealed the possible utilization of hydroxyl groups and amides in the reduction of silver ions and surface stabilization of the Ag NPs, respectively. Notably, the synthesized Ag NPs showed considerable antibacterial action against Escherichia coli even after 8 weeks of storage under ambient conditions. Thus, cell extracts of cultured callus of Catharanthus roseus could be explored as an ecofriendly platform for the synthesis of stable and functional nanoparticles.
Keywords: Antibacterial activity; Catharanthus roseus; callus extract; colloidal stability; green synthesis; silver nanoparticles.