Green synthesis of silver nanoparticles using Sorghum bicolor var. technicum seed extract, their characterisation and investigation of biological activities

Abstract Synthesis of nanoparticles can be long and costly processes using physical and chemical methods. Biological synthesis of nanoparticles is known to be cheaper and easier than other methods. In this study, silver nanoparticles (AgNP) were obtained by biological synthesis, also known as green synthesis, using Sorghum bicolor var. technicum (Körn) Stapf ex Holland seed extract, popularly known as sorghum. AgNPs were characterised by SEM, EDS, TEM, FT-IR, and UV-Vis Spectroscopy. SEM images confirmed that the shape of AgNPs was spherical. TEM analysis showed that the average sizes of AgNPs ranged from 51 to 56 nm. EDS analysis confirmed the presence of AgNPs by detecting a silver ion peak at 3 KeV. UV-Vis spectroscopy analyses indicated that the brown-burgundy colour of AgNPs exhibited maximum absorbance at 450 nm. The biological activities of the extract and AgNPs were investigated through antimicrobial, antibiofilm, antioxidant, mutagenic, and DNA cleavage activity analyses. The extract exhibited the highest MIC value against Gram-positive bacterium Bacillus subtilis (0.62 μg mL −1 ), whereas AgNPs demonstrated the highest antimicrobial activity specifically against Gram-negative bacterium Escherichia coli (0.31 μg mL −1 ). The antibiofilm results revealed that the extract displayed the highest percentage of biofilm inhibition against B. subtilis , while AgNPs exhibited notable efficacy against both Candida albicans yeast and Pseudomonas aeruginosa bacterium. The antioxidant activities were evaluated using DPPH • and ABTS •+ methods, and it was determined that both samples had high antioxidant activity. Mutagenicity of the extract and AgNPs were evaluated by the Ames/ Salmonella test using two strains of Salmonella typhimurium (TA98 and TA100). The mutagenic activity of the extract increased depending on the concentration for both strains, while AgNP did not show mutagenicity at any concentration. The agarose gel electrophoresis method showed that the extract and AgNPs cleaved DNA in the presence of an oxidising agent.