The biosynthesis of metal nanoparticles using medicinal plants is not only economical but also environmentally friendly as well as having miscellaneous biomedical applications.

Material and methods:
In the present study, silver nanoparticles were green-synthesized using an aqueous extract of Calendula officinalis. The synthesized AgNPs@C. officinalis was characterized by analytical techniques including EDX, FE-SEM, XRD, UV-Vis., and FT-IR. The anti-human colorectal cancer activities of AgNPs@C. officinalis were evaluated using MTT assay. The nanoparticles were formed in a spherical shape in the range of 38.05 to 75.41 nm for the particle size. On the other hand, the MTT assay was run to evaluate anti colorectal cancer activity of AgNPs@C. officinalis. In the cellular and molecular part of the study, the cells treated with AgNPs@C. officinalis were assessed by MTT assay for 48 h to determine the cytotoxicity and anti-human colorectal carcinoma properties on normal (HUVEC) and colorectal carcinoma cell lines, i.e. WiDr, SW1417 [SW-1417], and DLD-1.

In the antioxidant test, the IC50 values of AgNPs@C. officinalis and BHT against DPPH free radicals were 222 and 124 µg/ml, respectively. The viability of the malignant colorectal cell line decreased dose-dependently in the presence of AgNPs@C. officinalis. The IC50 values of AgNPs@C. officinalis were 430, 326, and 392 µg/ml against WiDr, SW1417 [SW-1417], and DLD-1 cell lines, respectively.

After the clinical study, silver nanoparticles containing C. officinalis leaf aqueous extract may be used to formulate a new chemotherapeutic drug or supplement to treat several types of human colorectal carcinoma.