Bioactivity-guided nanoparticle synthesis from Zingiber officinale and Mentha longifolia

To date, various reports have exhibited the antidiabetic activity of plant extracts, but this activity could be improved through the conversion of plant bioactives into metal nanoparticles. Aqueous plant extracts were prepared from two plants, Zingiber officinale and Mentha longifolia. Silver nanoparticles from aqueous plant extracts were synthesized and characterized through spectroscopic techniques, including ultraviolet–visible spectroscopy and Fourier transform infrared spectroscopy and scanning electron microscopy, in comparison with their respective plant extracts. After successful synthesis, these nanoparticles were evaluated for biological potentials of antioxidant, antimicrobial and antidiabetic activities. The nanoparticles of both plants offered outstanding antidiabetic potential, but the silver nanoparticles of Z. officinale showed the highest inhibition potential of 80.52% to α-amylase even at lower concentrations. The synthesized nanoparticles were found to be better antimicrobial agents against Bacillus subtilis and Escherichia coli as measured through a well diffusion assay as compared with aqueous extracts. These nanoparticles offered antioxidant potential that was better than that of their plant extracts but was slightly lower than that of the positive control gallic acid. This study gives a direction for improvement of the biological activity of plant-based medicine through green synthesis of silver nanoparticles.