Synergistic response of physicochemical reaction parameters on biogenesis of silver nanoparticles and their action against colon cancer and leishmanial cells

Physicochemical parameters include pH, temperature, the concentration of the AgNO₃, ratio of reactants, agitation and incubation period that act synergistically and provide a steering force to modulate the biogenesis of nanoparticles by influencing the molecular dynamics, reaction kinetics, protein conformations, and catalysis. The current study involved the bio-fabrication of silver nanoparticles (SNPs) by using the reducing abilities of Mentha longifolia (L.) L. leaves aqueous extract. Spectrophotometric analysis of various biochemical reactions showed that 3 mM of AgNO₃ at 120 °C in an acidic pH when mixed in 1–9 ratio of plant extract and AgNO₃ respectively, are the optimised conditions for SNPs synthesis. Different analytical techniques confirmed that the nanoparticles are anisotropic and nearly spherical and have a size range of 10–100 nm. The ∼10 µg/ml of SNPs killed ∼66% of Leishmania population and IC₅₀ was measured at 8.73 µg/ml. SRB assay and Annexin V apoptosis assay results showed that the plant aqueous extract and SNPs are not active against HCT116 colon cancer cells and no IC₅₀ (80% survival) was reported. ROS generation was quantified at 0.08 Φ, revealed that the SNPs from M. longifolia can generate free radicals and no photothermal activity was recorded which makes them non-photodynamic.