Optofluidic Biolasers in Tissues: Applications in Biology and Biomedicine

Abstract

Biolaser are an emerging technology for next generation biochemical detection and clinical applications. Laser-based detection offers the distinct advantages over fluorescence-based detection in terms of signal amplification, narrow linewidth, and strong intensity, leading to orders of magnitude increase in detection sensitivity. Recent advances have been made to achieve lasing from biomolecules and single cells. Tissues, which consist of cells embedded in extracellular matrix, mimic more closely the actual complex biological environment in living bodies, and thus are of more practical significance in medicine. The aim of this research is to develop optofluidic biolasers at the tissue level in order to provide a novel analytical tool for a wide range of biological and biomedical applications. During my research, several types of micro-laser cavities, such as optofluidic ring resonators and high-Q Fabry-Pérot resonators were implemented to achieve lasing in tissues. Distinct and controllable laser emissions from various tissues thus enable highly multiplexed/multifunctional detection with superior contrast and high spectral/spatial resolution. In terms of biological applications, we first demonstrated chlorophyll lasing with intrinsic gain medium extracted from leaves, suggesting the possibility to lase with natural biological tissues. In addition, we developed a versatile tissue laser platform in which biological tissues were doped with different dyes and sandwiched within a high-Q Fabry-Perot cavity. Detailed investigation on how tissue structure/geometry, tissue thickness, and staining dye concentration affect the tissue laser was conducted. To signify potential implementations of the tissue lasers in biomedicine, lasing in two major types of clinical tissues were investigated, including liquid biopsy and surgical biopsy. Herein, we demonstrated the first “blood laser” using the only FDA approved near infrared dye, Indocyaine Green, in human whole blood with the ICG concentration within the normal range of clinical dosage. Furthermore, we developed the first “laser emission-based microscope” (LEM) for improved cancer evaluation by mapping the lasing emissions from nuclear biomarkers in human lung and colon cancer tissues. As a proof-of-concept, tissue samples from patients labelled with cancer biomarkers were tested while an excitation laser beam was scanned to build a laser-emission image. It is found that nuclei in the cancer and normal tissues have vastly different lasing thresholds due to different expressions of nucleic acids and nuclear proteomic biomarkers, which enables the LEM to distinguish, with a high contrast, the cancer and normal tissues, and the cancer tissues with and without nuclear proteomic biomarkers. Significantly, the LEM has demonstrated a great potential to diagnose early stage cancer tissues with a high sensitivity of 97.5%. We also presented the wavelength-multiplexed immuno-lasing capability of LEM. As a final remark, we achieved lasing in living neurons/neuronal networks and employed laser emission to detect the subtle transients of intracellular calcium dynamics in neurons in vitro. Calcium imaging and recording of spontaneous neuronal activities were demonstrated with the “neuron lasing” method, in which the relative changes were significantly improved 1000 fold compared to fluorescence-based measurement. This thesis marks a critical step towards eventual clinical and biomedical applications of optofluidic biolasers, which may find broad use in precision medicine with on-chip cancer screening and immunodiagnostics, as well as in brain-on-chip devices, neuro-analysis, tissue engineering, and fundamental cell biology.