*2.5. Biosynthesis of AgNPs*

Silver nitrate (Cat. no. 10018461; Sinopharm, Shanghai, China) was used to synthesize AgNPs according to [9], with slight modification. Briefly, 10 mL of CFSs were added to 90 mL of 3 mM AgNO<sup>3</sup> aqueous solution in a 250 mL Erlenmeyer flask and then incubated at 30 ◦C in a rotary shaker at 200 rpm for 3 d in the dark. As a control, 10 mL of NA broth with the same volume of AgNO<sup>3</sup> was used. The successful biosynthesis of AgNPs will convert the colour from yellow light to dark brown, which can be determined by using UV–Visible spectrometry (Shimadzu UV-2550 spectrometer) in the wavelength range of 200–800 nm at a resolution of 1 nm. The resulting pellets were collected from AgNPs by centrifugation at 10,000× *g* for 20 min, purified by washing twice with sterile doubledistilled water (ddH2O) and stored at −80 ◦C.
