Abstract: Due to the widely applications in antimicrobial and biomedicine,the synthesis of silver nanoparticles (AgNPs) have received increasing attention.In this work,a novel formation method of AgNPs by using the jujube aqueous extract was reported,and the antioxidant and antibacterial activities of synthetic AgNPs were assessed.By evaluating the pH of solution,material proportion and reaction time,the optimal reaction conditions (pH 9.0,jujube aqueous extract∶AgNO₃ =1∶1,reaction time：4 h) were confirmed.The results of dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that the synthetic AgNPs were spherical in shape with an average size of 25.99 nm and were covered by the anion (zeta potential:-29.6 mV).The antioxidant activities were assessing by calculating the free radical scavenging rate for DPPH.When the concentration of AgNPs increased to 100 μg/mL,the free radical scavenging rate was 83% indicating a good antioxidant activity.Furthermore,the AgNPs generated by jujube aqueous extract revealed significant inhibition on the growth of E. coli and S. aureus,where the MIC values were 100 and 125 μg/mL,respectively.The enhanced antibacterial activity may result from the synergistic effect between AgNPs and active compounds of jujube aqueous extract.Lastly,the formation mechanism of AgNPs by using jujube aqueous extract were preliminary discussed based on the pH-dependent experiment and the result of zeta potential.These results indicated that the reductive polysaccharide in the jujube aqueous extract may play an important role in the formation of AgNPs.

Key words: jujube aqueous extract, ultrasonic method, silver nanoparticles, antibacterial activity,antioxidant activities