Biological effects of gold nanoclusters are evaluated by using silkworm as a model animal

In this paper, Bombyx mori silkworm was used as a model animal to evaluate the biological effects of BSA-stabilized gold nanoclusters (BSA-Au NCs) via characterizing the growth status and silk properties of silkworms; the uptake of BSA-Au NCs by silkworms was realized by intravascular injection (the most dose of Au is 9.38 μg/silkworm). The results show that BSA-Au NCs have no obvious negative effects on the growth status of silkworms. WAXS and infrared results demonstrate that the crystalline or secondary structures of BSA-Au NCs-silks are not changed, but there is a slight increase in the helix/random coil content and a little decrease in the size and content of β-sheet compared with control-silks, suggesting that BSA-Au NCs confine the conformational transformation of silk fibroin to β-sheet from helix/random coil. Thermogravimetric analysis and tensile test results show that the thermal stability and mechanical properties (elongation at break, breaking strength and toughness modulus) of the BSA-Au NCs-silks are not weakened and the toughness modulus of the BSA-Au NCs-silks is increased, which may be attributed to the increase in the helix/random coil content. ICP-MS results demonstrate the accumulation and biodistribution of Au element in midgut, fat body and silk gland after the injection of 120 h, indicating that Au mainly distributes in midgut. In summary, BSA-Au NCs show no significant negative effect on silkworm when the dose of Au is below 9.38 μg/silkworm (about 6.25 mg kg−1). This study provides an efficient method for evaluating the biological effects of NCs, which will have a potential use in the biochemical field.