Elastomer-based whispering gallery mode microlasers with low Young's modulus for biosensing applications

Sensing biological forces with microscopic lasers is an emerging technique that offers significant advantages over conventional fluorescent probes and imaging-based techniques. However, the limited availability of suitable deformable or elastic microlaser materials is restricting the scale of forces that can be detected which strongly narrows their overall applicability. Here, we describe the synthesis of spherical whispering gallery mode microbead lasers from a commercially available elastomer material in a microfluidic system with high viscosity. Upon doping with an organic dye, the microbeads show multimode lasing with thresholds in the range of 2-11 nJ. Measurements of the mechanical properties reveal that the width of the laser modes is directly proportional to the applied external force. The measured mean Young's modulus is 36 kPa, comparable to the stiffness of single cells and soft tissues. We also demonstrate that elastomer microlasers are stable under cell culture conditions for several days and observe splitting of the laser modes for intracellular microlasers. The observed properties render elastomer microlasers as a robust material platform for biointegrated lasers that also allows further tuning of the mechanical and optical properties for tailored force sensing inside cells, tissues, and small animals.