Solid-state low-threshold hemispherical shell-shaped protein whispering-gallery mode laser

Protein-based whispering-gallery mode (WGM) lasers offer great potential for biosensing due to their biodegradability, biocompatibility, and non-toxicity. Here, we report a solid-state hemispherical shell-shaped protein WGM laser (hspWGM laser) made by forming silk fibroin shells on glass substrates and coating them with red fluorescent protein mCherry. The device (∼1.5 mm diameter) demonstrated stable lasing, short-term room-temperature storage, and a low lasing threshold (10.17 µJ/mm²). Central wavelength characteristics were tunable by adjusting device geometry. These results provide a foundation for developing biodegradable, protein-based biosensors and implantable optical devices.