Chiang Mai Journal of Science

     Red Onion (Allium cepa L.) Peels (ROP) is an unwanted agricultural byproduct after cooking but it is rich with bioactive compounds such as phenolics, flavonoids, flavanols and quercetin. In this work, we employed the extract of ROP as a reducing agent in green synthesis of silver nanoparticles (AgNPs) and investigate their antibacterial properties. The concentration of ROP used in this research for green synthesis is 0.003, 0.005, 0.007, and 0.009 wt%. AgNPs shapes are found to be quasi-spherical shape, flat triangular, hexagonal shapes and sea urchin clusters depending on the concentration of ROP. The obtained zeta potential value is approximately -40 mV indicating good stability of AgNPs colloidal solution. The antibacterial potency of synthesized AgNPs with sharp edges (sea urchin clusters) shows superior antibacterial effect on gram-negative bacteria toward Pseudomonas aeruginosa (P. aeruginosa) which is superior to Chloramphenicol. The inhibition zone diameter of synthesized sea urchin-like structure of AgNPs with ROP concentration of 0.007 wt% is 16.2 ± 0.9 mm compared with the inhibition zone diameter of Chloramphenicol (13.0 ± 0.0 mm). Furthermore, these AgNPs (0.007 wt% ROP) are further applied by coating on air filters. The filters show superior antibacterial potency with inhibition zone diameter of 21.6 ± 0.5 mm compared to uncoated air filter (0.0 ± 0.0 mm). This result suggests that our synthesized AgNPs used in this study show good potential for use as an antibacterial agent for antibiotic-resistant bacteria in air cleaning devices, which is a significant aspect of our work whereby harmful airborne pathogens can be inactivated and removed before they can infect vulnerable post-surgery patients.