Green synthesis of silver nanoparticles from Alpinia galanga extract with microwave irradiation and antibacterial activity against Escherichia coli

Background: This study deals with the rapid green synthesis of silver nanoparticles (Ag NPs) by microwave irradiation using water extract of Alpinia galanga as a reducing agent. Methods: The effect of concentrations of water extract and silver nitrate aqueous solution (1 mM) on the synthesis was investigated using the ratios 1:1, 1:5, 1:10, and 1:20. The formation of Ag NPs was observed after being microwaved for 30, 60, 90, 120, 150, and 180 seconds. Results: The best Ag NPs were produced from the ratio of 1:10 after 180 s irradiation, confirmed by the optimum absorbance at 450 nm using a UV-visible spectrophotometer. Transmission electron microscopy analysis showed that the size of the Ag NPs was 50 nm. Their antibacterial activity was determined using Resazurin microtiter assay against Escherichia coli, and the results showed that it inhibited 94.4% of E. coli. It was significantly different (p < 0.05) with the inhibition of extract and Amoxsan, which inhibited 71.1% and 85.8% of E. coli, respectively. Conclusion: The use of microwave irradiation on the synthesis of silver nanoparticles using Alpinia galanga extract as a reducing agent appears to be rapid and eco-friendly.