3D micro-printed polymer limacon-shaped whispering-gallery-mode microlaser sensors for label-free biodetection.

Optical whispering-gallery-mode (WGM) microlaser sensors have garnered significant attention in biological sensing due to their distinct advantages, including strong light-matter interactions and versatile sensing modalities. However, challenges remain in developing WGM microlaser sensors that can serve as building blocks for large-scale integrated sensor platforms in lab-on-chip applications. In this work, we present a 3D micro-printed polymer limacon-shaped WGM microlaser sensor for on-chip integrated biosensing. The WGM microlaser sensor has both high-quality factor (Q factor) and directional emission properties, making it ideal for high-sensitive on-chip biosensing platforms using a far-field coupling scheme. Experimental results showed that the 3D micro-printed WGM laser sensor has a very low lasing threshold of 3.87 µJ/mm² and a narrow lasing linewidth of about 30 pm. Remarkably, experiments have shown that the sensor can detect human IgG with a detection limit of around 70 ag/mL, revealing its potential for ultralow-limit detection of biomarkers in early disease diagnosis.