Single-cell pump probe imaging of intrinsic chromophores identifies diagnostic marker and therapeutic target of diseases
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When photons transport inside the biological samples, the interaction between photons and biological analytes enable us to map a specific diagnostic biomarker for disease. However, biological media are composed of discrete scattering particles. Propagation of photons are highly attenuated due to scattering and absorption, which makes it challenging for clinical diagnosis. There is a need for identifying biomarkers for precision medicine and diagnosis. Chromophores exists endogenously in various organisms and cells; however, their potential of precision diagnosis and treatment still remain under-explored. Note that lots of research has been harnessed, for example, autofluorescence from FAD and NADH has been used for cancer diagnosis, but the potential of this area needs to be further mined, as most of the intrinsic chromophores has considerably low fluorescent quantum yield. This thesis illustrates how we came with an absorption-based chemical microscopy approach to study these chromophores at single cell level, and that these opens new discoveries for diagnosis and treatment. It first outlines how transient absorption microscopy is utilized to diagnose diabetes at single cell level, and then this technique enabled the discovery of a molecular signature, staphyloxanthin photolysis, for efficacious treatment of methicillin-resistant Staphylococcus aureus (MRSA)-caused infections through photo-disassembling its cell membrane microdomains. Besides staphyloxanthin, we also uncovered that catalase, which exists in most of the microbes (Candida auris, and drug-resistant gram-negative pathogens included), can be efficiently photo-inactivated, thus enabling these catalase-positive pathogens to be sensitive to exogenous antimicrobial agents. We also utilized stimulated Raman scattering microscopy to map the orientation amphotericin B, a golden standard antifungal agent, in a single fungal cell membrane to reveal its working mechanism. Collectively, nonlinear chemical imaging offers a profound tool to visualize in situ microbial metabolic dynamics, and discover molecular markers for precision treatment and diagnostic purposes.