Hyperspectral confocal imaging of whispering-gallery-mode microlasers for bio- and ecophotonic applications

Abstract

Microscopic lasers are an emerging platform for biophotonic applications. These lasers are free-standing particles with diameters of hundreds of nanometres to a few micrometres. They generate coherent emission characterised by bright and narrow lasing peaks at unique spectral positions. Particularly in the field of cell biology, such microlasers are an attractive tool for a range of applications, owing to their straightforward integration into living cells. Intracellular microlasers are optically excited and their distinct lasing spectra are recorded using custom spectral imaging systems. These spectra can serve as barcodes for tracking applications, and they can be used as intracellular sensors due to the dependence of the lasing spectra on the optical properties of their immediate environment.

Here, a custom imaging system for high-throughput microlaser readout was developed to allow capitalising on the great potential of microlasers for high-throughput measurements with single-cell specificity. This hyperspectral confocal microscope allows automated highspeed 3D-scanning of large volumes, recording a high-resolution spectrum at each voxel. The setup is predominantly used to record spectra from polystyrene microbead lasers and semiconductor nanodisk lasers. The semiconductor materials forming the nanodisk lasers were also improved for integration with the high-throughput microscope and for deep-tissue applications.

Following these advances, applications of bio-integrated microlasers were extended to larger and more complex systems, including 3D cell culture models and small animals. Due to the high-speed and high-resolution readout, this has allowed dynamic sensing with multiple microlasers in parallel, which was used for contractility sensing in a cardiac cell culture model. The spectral shifts of the measured lasing peaks were used for quantitative measurements of the local refractive index by developing and employing appropriate mathematical models. Further, the tracking capabilities were demonstrated in a 3D epidermis model, where the cellular migration was followed, and in small marine animals.