BACKGROUNDBiosynthesis of silver nanoparticles (AgNPs) is considered a green method. Sunlight could induce the synthesis of AgNPs with bacteria and plant biomass, while animal and fungus biomass have not been investigated for synthesis of AgNPs under sunlight radiation. RESULTSUnder 80 000 lx sunlight intensity and 4 mg mL(-1) of tryptone solution, the maximum AgNPs yield was obtained after 60 min, and the Ag+ (1 mmol L-1) conversion rate reached 98 2%. Transmission electron microscopy revealed that T-Ag (tryptone-mediated) were circular and oval, with an average diameter of 11.63 +/- 4.17 nm, and Y-Ag (yeast extract-mediated) displayed similar shape and size to T-Ag. X-ray diffraction confirmed that T-Ag and Y-Ag were in the form of nanocrystals. As-prepared AgNPs showed obvious antimicrobial activity against B. subtilis and E. coli. Capping with peptides helped to maintain colloidal stability of AgNPs. Without sunlight, AgNPs showed high stability at pH 7-11 due to high -potential values, while the stability was destroyed at pH 4. Further exposure to sunlight for 48 h also resulted in sedimentation of AgNPs. CONCLUSION

Sunlight could induce tryptone and yeast extract to synthesize AgNPs, and the stability of AgNPs could be regulated by capping peptides, pH, and sunlight exposure. (c) 2013 Society of Chemical Industry