Distinguishing small molecules in microcavity with molecular laser polarization

Abstract

Microlasers have emerged as a promising approach for the detection or identification of different biomolecules. Most lasers were designed to reflect changes of molecular concentration within the cavity, without being able to characterize biophysical changes in the gain medium. Here, we report a strategy to extract and amplify polarized laser emissions from small molecules and demonstrate how molecular rotation interplays with lasing at the nanoscale. The concept of molecular lasing polarization was proposed and was first evidenced to increase accordingly as the fluorophore binds to larger biomolecules in a microcavity. By detecting the molecular rotational correlation time through stimulated emission, small molecules could be distinguished, while conventional fluorescence polarization cannot. Theoretical models were developed to elucidate the underlying mechanisms. Finally, different types of small molecules were analyzed by adopting a Fabry-Pérot optofluidic laser. The results suggest an entirely new tool to quantify small molecules and guidance for laser emissions to characterize biophysical properties down to the molecular level.