Daehyuk's Seminars

Developing label-free biochemical imaging using quantitative phase imaging and mid-infrared photothermal effects

Abstract: Quantitative phase imaging (QPI) has been widely recognized for its ability to provide high-contrast, label-free images. Spatial light interference microscopy (SLIM), based on common-path interferometry, offers exceptional phase stability. However, the system response, particularly the relationship between illumination geometry and image contrast, has not been thoroughly studied. Under the weak scattering approximation and within the transmission cross-coefficient (TCC) framework, spatial contrast can be tuned to specific feature sizes, providing a valuable tool to optimize quantitative phase measurements in biological samples. Furthermore, a conventional Zernike phase contrast microscope was modified to enable single-snapshot phase measurement via polarization multiplexing. Four phase-shifted interferograms can be captured simultaneously in different polarization channels, eliminating sequential measurements. This enhancement improves temporal resolution (up to 100 fps), reducing motion artifacts and enabling the extraction of dynamic contrast, which revealed organelle-specific features in live neurons through temporal spectral analysis. To expand the system’s capabilities, mid-infrared photothermal effects will be integrated, providing bond-specific hyperspectral contrast. This approach overcomes QPI’s fundamental limitation—lack of molecular specificity—without the need for extraneous labels. By combining high-resolution, dynamic, and molecular-specific imaging, this work aims to advance the quantitative understanding of biomechanical processes through multidimensional contrast.

By Minsung Kwon, Beckman Institute for Advanced Science and Technology, Faculty Advisor, Rohit Bhargava

A defined synthetic ECM and automation for reproducible breast cancer spheroids

Abstract: Naturally derived extracellular matrices such as reconstituted basement membrane (rBM) and Matrigel are widely used for 3D breast cancer spheroid culture, but their poorly defined composition, batch-to-batch variability, limited tunability, and high cost significantly limit reproducibility and mechanistic insight. In particular, the narrow stiffness range accessible in Matrigel and the confounding effects of compositional heterogeneity hinder systematic interrogation of microenvironmental stress responses, including hypoxia and therapeutic perturbations. To address these limitations, we developed a fully defined synthetic extracellular matrix (sECM) platform with independently tunable stiffness, adhesive ligand density, and degradability, enabling reproducible 3D culture while isolating key physical and biochemical variables. Benchmarking against Matrigel demonstrated improved consistency in spheroid morphology, proliferation, and growth dynamics across breast cancer models, while maintaining viability and functional behavior. Using this platform, we interrogated tumor responses to hypoxia, drug treatment, and molecular perturbations within a controlled microenvironment. Bulk spheroid embedding approaches generate heterogeneous populations that vary in size, spatial position, and local microenvironmental exposure, obscuring tumor-specific stress responses. To overcome this, we developed manufactured tumor models (MTMs) by embedding single, size-controlled spheroids within sECMs using an automated liquid handling workflow. This standardized approach minimizes population averaging and human error, enabling reproducible, tumor-by-tumor resolution of stress-induced phenotypes. Together, the sECM–MTM platform provides a scalable and high-fidelity framework for mechanistic studies of breast tumor biology.

By Revathi Manoharaan, Beckman Institute for Advanced Science and Technology, Faculty Advisor: Rohit Bhargava