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Anisotropic silver nanoparticles were coated on silk fibers to obtain colorful silk with good antibacterial properties. Different morphologies of silver nanoparticles gave different colors to the silk fibers, because of changes in the localized surface plasmon resonance of the nanoparticles. More efficiently, mixing of different silver nanoparticles in different proportions extended the range of colors. Unlike the conventional silk dyeing process, which is energy-intensive, the coloration process with silver nanoparticles was achieved at room temperature. The silk fibers displayed strong adsorption ability for silver nanoparticles during the coloration process. The modified silk fibers exhibited different bright colors as the silver nanoparticles on the surface of the fibers varied. Significantly, the silk fibers treated with silver nanoparticles showed significant antibacterial abilities against Escherichia coli. Moreover, good color fastness to washing was achieved through coating of polydimethylsiloxane on the surface of silk treated with silver nanoparticles.

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Silk cocoons provide protection to silkworm from biotic and abiotic hazards during the immobile pupal phase of the lifecycle of silkworms. Protection is particularly important for the wild silk cocoons reared in an open and harsh environment. To understand whether some of the cocoon components resist growth of microorganisms, in vitro studies were performed using gram negative bacteria Escherichia coli (E. coli) to investigate antibacterial properties of silk fiber, silk gum, and calcium oxalate crystals embedded inside some cocoons. The results show that the previously reported antibacterial properties of silk cocoons are actually due to residues of chemicals used to isolate/purify cocoon elements, and properly isolated silk fiber, gum, and embedded crystals free from such residues do not have inherent resistance to E. coli. This study removes the uncertainty created by previous studies over the presence of antibacterial properties of silk cocoons, particularly the silk gum and sericin.