Naturally Bred Korean Silkworm Cocoon Showing Strong Green Fluorescence and Its Textile-Based Environmental Sensing Applications

Mulberry silkworms have provided many valuable byproducts to humans for 5,000 years. However, numerous possibilities for their utilization still exist owing to the countless varieties of silkworms. Here, we report the application of Yeonnokjam silk (pistachio silk, PS), one of the characteristic silk varieties in Korea, as a smart fabric environmental sensor. Unlike the previously reported extrinsically modified silk varieties, this new silk textile emits fluorescence under external stimuli. PS cocoons were exposed to different concentrations of HCl vapors. Due to the large surface-to-volume ratio of the cocoon textile, a very low concentration (5 ppm) of HCl vapor can be detected by reading the decrease in the fluorescence intensity. At a lethal concentration (3000 ppm), an instantaneous fluorescence response is obtained. Additionally, the fluorescent pigment in PS can respond to temperature and can be extracted using ethanol, indicating that PS exhibits temperature and ethanol-sensing capabilities. The findings of this study prove that natural PS can be used in bio-optical applications.