Bio-laser emission imaging and analysis of optical resonators

• Main Author: Ang, Randall Jie
• Other Authors: Y. C. Chen
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Science::Physics
• Online Access: https://hdl.handle.net/10356/139107
• Institution: Nanyang Technological University

Nucleus-cytoplasmic ratio has been the conventional method used to access the malignancy of cells. Current detection techniques use histological methods to observe samples obtained from biopsy via fluorescence optical microscopy. Laser emission microscopy offers a more sensitive and accurate detection due to sharper, narrower and more amplified signal output compared to fluorescence. Hence, the purpose of this final year project is to explore the benefits of using a Fabry–Pérot based microcavity laser in detecting nuclear variations. This is achieved by studying how the size and concentration of gain molecules within the nucleus affect output characteristic of laser emission which includes laser modes, intensity, spectrum, and threshold. In this study, 4 experiments were conducted utilising spectrum analysis and hyperspectral imaging. The first and second experiments investigated the relationship between laser characteristics and changes in nuclear size by using silica microsphere beads and dye-doped liquid crystals droplets as artificial cell models for label-free and labelled detection respectively. The third experiment determined how the lasing threshold varied with the concentration of dye-doped liquid crystals, and the final experiment explored hyperspectral imaging of C2C12 cells stained with fluorescent dyes. The results revealed that there is a directly proportionate relationship between the size of the artificial cell model and the transverse laser modes observed using hyperspectral imaging. Furthermore, as dye concentration inside the liquid crystal droplet increases, the lasing threshold starts to decrease. This relationship is evident either by analysing the transverse mode patterns or observing the unique threshold behaviours from the laser emission spectrum, all while varying the input pump energy. Finally, it was found that the most suitable condition to produce transverse modes in cells was when the fluorescent gain medium is present both inside and outside of the cell. From the findings, it was found that laser emission spectrum and transverse modes are affected by the size and refractive index distribution within the cell, hence biological lasers could potentially be used for sensitive cellular sensing and imaging purposes. A QR code method was also developed to characterise cells by sorting the transverse modes observed from hyperspectral imaging. This FYP will be essential for cancer studies especially in early diagnosis and detection of tumours.