Phytosynthesis of Ag nanoparticles from Mentha longifolia: their structural evaluation and therapeutic potential against HCT116 colon cancer, Leishmanial and bacterial cells

The present investigation was aimed to phytosynthesize silver nanoparticles (AgNPs) by utilizing aqueous extract of Mentha longifolia branches to reduce mass Ag into Ag° and evaluation of their potential to treat HCT116 colon cancer, Leishmanial, and bacterial cells. A characteristic Surface Plasmon Resonance (SPR) band to confirm synthesis was observed at ~ 450 nm of λ light by UV–Visible spectrophotometer. SEM and AFM micrographs unraveled that nanostructures are anisotropic, spherical and have a size under ~ 100 nm. Particle size analysis confirmed that the majority of the nanoparticles exist in ~ 6–20 nm of the size range. EDX investigation represented the highest peak of Ag with ~ 74% signal intensity. FTIR analysis confirmed the presence of the N–H (amine) group, C–N (cyanide) group and C≡C (alkynes) stretch as the surface capping agents. AgNPs were found biocompatible against human RBCs at a lower dose and LD₁₀₀ was recorded as 117 μg/ml, which shows that a very high dose of AgNPs is required to cause toxicity to RBCs. The selective dose-dependent response of AgNPs was reported against Leishmania tropica and decreasing the dose of the nanoparticles resulted in increasing the survival rate of the pathogen (P < 0.05);10 μg/ml of AgNPs killed practically 67% of cells. Antibacterial action against plant bacterial pathogens was seen between 2 and 12 μg/ml. Annexin V apoptosis analysis and SRB examination showed that the plant aqueous extract and AgNPs are incapable to control the development of HCT116 colon cancer cells and only 3.77% cells indicated apoptosis. The results show the biocompatibility of phyto-functionalized nano-silver to selectively treat Leishmania and plant bacterial pathogens.