Ultrastable Colloidal Quantum Well–Liquid Crystal Microlasers for Real‐Time and Ultrasensitive Cellulase Biosensing

ABSTRACT Microlaser biosensors can convert subtle biochemical events into highly resolved optical signals, but their practical use is often restricted by the poor photostability and short lifetime of organic gain media, as well as inefficient biochemical‐to‐photonic signal transduction. Here, we report an ultrastable colloidal quantum well (CQW) microlaser biosensor for real‐time, quantitative, and ultrasensitive cellulase detection. To our knowledge, this is the first use of CQWs as gain media for biochemical reaction sensing. Highly emissive CdSe/Cd 1 − x Zn x S core/thin‐shell CQWs with a photoluminescence quantum yield of ∼0.95 were deposited on a PMMA microfiber and subsequently integrated with a 5CB liquid‐crystal phase containing lauryl glucoside to form an active whispering‐gallery‐mode microcavity. Enzymatic hydrolysis disrupts interfacial assembly, induces liquid‐crystal reorientation, and produces measurable wavelength shifts. The microlaser shows a low lasing threshold of ∼17.2 µJ cm − 2 , excellent operational stability, and no detectable signal attenuation over 40 days. With cysteine‐assisted activation, it achieves a cellulase detection limit of 1 ng mL − 1 , representing a two‐orders‐of‐magnitude improvement over conventional polarized optical readout, while retaining high selectivity and inhibition‐verified enzymatic specificity. This work establishes CQWs as photostable gain media for long‐term biosensing and provides a general strategy for converting biochemical interfacial reactions into amplified photonic outputs.