Light sheet microscopy and spectroscopy of whispering gallery mode microlaser particles

Abstract

Whispering gallery mode microlasers are a recently developed sensing tool which can be used to make localised measurements of refractive index changes in a biological tissue through examination of their emission spectrum. This allows the direct quantification of various mechanical or physical properties in microscopic organisms. Recently these microlasers have found applications in studies in range of sample types including in vitro samples such as individual cells or three-dimensional multicellular spheroids as well as in vivo samples such as zebrafish embryos and larval fruit flies. These studies have typically made use of standard brightfield illumination and fluorescence microscopes with a coupled spectrometer to perform measurements. However, for detailed studies of large 3D tissues displaying a large degree of structural heterogeneity it is essential to employ more advanced microscopy techniques to allow full 3D imaging of the sample with high resolution. To this end some studies have performed confocal microscopy to acquire 3D images of samples with combined microlaser spectroscopy. Confocal microscopy has limitations however, with its point scanning illumination style having limited temporal resolution as well as causing sample degradation due to phototoxicity effects. To mitigate this one can an implement light sheet microscopy which makes use of a line-based illumination geometry to allow whole planes of a sample to be imaged in one acquisition whilst minimising phototoxic effects. In this thesis, a dual modality system consisting of a light sheet fluorescence microscope coupled to a spectrometer for use in microlaser studies is designed and built allowing implementation of combined high-resolution imaging and microlaser spectral analysis. After construction, the effect of the light sheet illumination of the microlasers is examined with regards to the coupling behaviour between the sheet and the microlaser. The performance of the system is demonstrated through measurements of the absolute refractive index using microlasers inserted into an agarose sample and in fixed zebrafish tail muscle tissue. Finally, the muscles of fruit fly larva samples are imaged in vivo using the light sheet system and the prospect of using these samples for cardiology studies is discussed.

Date of Award	2 Dec 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Malte Gather (Supervisor) & Marcel Schubert (Supervisor)