Ultrafast all-optical laser scanning microscopy for high-throughput imaging cytometry

Abstract

High throughput imaging technologies provide exhaustive information for indepth knowledge of biological systems, which are complex and heterogeneous by nature. However, available techniques face common trade-off among resolution, throughput and sensitivity, which hinders their application for large-scale single-cell assay. By adopting spatial-temporal encoding, single-pixel imaging techniques such as optical time-stretch microscopy offer ultrafast pixel read-out rate that is orders of magnitude higher than conventional technologies. Nevertheless, the excessive group delay dispersion required restrains optical time-stretch microscopy from utilizing laser sources outside near infrared regime. In this thesis, a novel high-throughput image cytometer based on an alloptical laser scanning technique termed free-space angular-chirp-enhanced delay (FACED) is introduced. Compared with optical time-stretch microscopy, FACED microscopy offers higher diffraction limited resolution with similar scan speed due to its compatibility with visible laser sources, capable of resolving sub-cellular structure at a throughput beyond 20,000 cells/second. In addition, the lift of light source limitation makes FACED widely compatible with popular molecular contrast agents such as various immunofluorescent labels. The first chapter is dedicated for introducing the motivation behind enabling high-throughput cellular assay as well as the advantages of FACED over optical time-stretch microscopy. A review of the working principle and design criteria of FACED microscopy is provided as introduction. In the second chapter, the capability of FACED imaging flow cytometry to capture cellular images with subcellular resolution and cell content specificity is demonstrated. For demonstration, biological events, such as cell-death process in this work, are characterized on a population level based on biophysical and biomolecular features obtained from the images. In the third chapter, the ongoing efforts towards building a multimodal FACED microscopy for practical large-scale cellular assay are summarized. Compared with the first generation FACED imaging cytometry platform, the second generation enables quantitative biophysical and biomolecular features retrieval, namely quantitative phase imaging and fluorescence microscopy. The design criteria is justified alongside accompanying theoretical and practical challenges. Preliminary results of cell images within ultrafast microfluidic flow are demonstrated, which consist of quantitative phase and fluorescent images recorded simultaneously. Finally, future improvement and biological applications are discussed.