OSC Dissertation Defense: Jiabin Chen

First, DUV microscopy was developed to exploit the strong endogenous absorption of nucleic acids near 260 nm, providing intrinsic nuclear contrast in cytology without staining. For intact tissue, epi- and oblique illumination were investigated, along with a uniform illumination scheme using a single light-emitting diode (LED) for high-contrast surface imaging. These studies demonstrate rapid visualization of superficial morphology but also reveal the depth limit imposed by strong ultraviolet absorption and scattering. Second, chromatic confocal microscopy was investigated using a diffractive hyperchromatic objective. Intentional longitudinal chromatic aberration focuses different wavelengths at different depths, spectrally encoding axial information and reducing the need for mechanical scanning, though penetration remains limited by tissue scattering. Third, NIR multiphoton microscopy, including two- and three-photon excitation and second-harmonic generation, was used to visualize endogenous cellular and extracellular structures at greater depths, with tradeoffs among penetration depth, signal strength, system complexity, and optical exposure.

 

Together, these studies establish a wavelength-dependent framework for label-free biomedical imaging: DUV microscopy provides strong intrinsic contrast at shallow depths, chromatic confocal microscopy enables optical sectioning at intermediate depths, and multiphoton microscopy reaches deeper tissue. This work shows how wavelength, contrast mechanism, and system design can be jointly engineered to reduce reliance on staining and sectioning while enabling multiscale imaging of cells and tissues.