Magnetic nanoparticles embedded in microlasers for controlled transport in different sensing media

In recent years, whispering gallery mode microlasers have attracted tremendous interest in sensing due to their ultra-high sensitivity at atomic levels. However, due to the non-magnetic properties, it is difficult to locate the microlasers at hard-to-reach positions, thus, limiting their sensing potential in many in-vitro and in-vivo applications. In this work, we report magnetic microlasers fabricated by encapsulating Ni_0.2Zn_0.8Fe₂O₄ magnetic nanoparticles (MNPs) within their cavity made of bovine serum albumin. The presence of MNPs allows the transportable actuation of the magnetic microlasers while maintaining lasing emission characteristics. Microlasers with various concentrations of MNPs are investigated to identify the optimum concentration that can balance a good magnetization, a low lasing threshold, and a high quality (Q) factor. These magnetic microlasers can be employed for sensing applications where sensors need to be navigated through different sensing media. As a proof of concept, we observed a clear shift of lasing wavelength of a magnetic microlaser while dragging it through different adjacent media by magnetic navigation. This result demonstrates the potential applications of magnetic microlasers for future biological and chemical applications.