Compact Quantum-Dot Lasing Microbeads for Multiplexed Bio-Imaging

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Recently, there has been growing interests in using microbeads in a lasing or stimulated emission regime to enhance spectral brightness and multiplexing capability. Here, we demonstrate quantum dot microbeads capable of generating single-peak laser emission with a sub-nanometer linewidth.^[1]The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single-mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 μm in the air. Sub-nm lasing emission is maintained even inside high-index surroundings, such as organic solvents and biological tissues. The feasibility of intracellular tagging and multi-color imaging <i>in vivo</i> is demonstrated. Multicolor imaging with proposed microbeads shows greatly enhanced spectral density and color-multiplexing capability compared to conventional fluorescence imaging.<br/><br/>[1] K.-H. Kim et al. <i>Adv. Funct. Mater.</i> <b>2021</b>, 2103413