Light Sheet Reflectance Microscopy

Many human diseases are diagnosed by the histopathological analysis of suspicious lesions where cellular morphological changes are examined at microscopic resolution. Reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) are two optical imaging technologies that can visualize microscopic details of the tissue without having to remove or process the tissue. However, both RCM and OCT are generally expensive and have either limited field of view or low resolution. Light sheet microscopy, an imaging modality utilizing a thin sheet of light for illumination, can achieve comparable resolution compared to RCM while providing a field of view comparable to OCT. The light sheet microscope can be made at low cost by using a consumer-grade CMOS camera, an inexpensive light source such as an LED, and low-NA objective lenses. In this thesis, we have developed two simple light sheet microscopes with a goal of rapidly visualizing cellular details of the intact tissue either in vivo or ex vivo. The first utilized near-infrared illumination and the second utilized visible illumination. Preliminary imaging results showed that cellular details of the tissue can be visualized over a large field of view in both animal and human tissues

Polarization-resolved extinction and scattering cross-section of individual gold nanoparticles measured by wide-field microscopy on a large ensemble

We report a simple, rapid, and quantitative wide-field technique to measure the optical extinction $\sigma_{\rm ext}$ and scattering $\sigma_{\rm sca}$ cross-section of single nanoparticles using wide-field microscopy enabling simultaneous acquisition of hundreds of nanoparticles for statistical analysis. As a proof of principle, we measured nominally spherical gold nanoparticles of 40\,nm and 100\,nm diameter and found mean values and standard deviations of $\sigma_{\rm ext}$ and $\sigma_{\rm sca}$ consistent with previous literature. Switching from unpolarized to linearly polarized excitation, we measured $\sigma_{\rm ext}$ as a function of the polarization direction, and used it to characterize the asphericity of the nanoparticles. The method can be implemented cost-effectively on any conventional wide-field microscope and is applicable to any nanoparticles

Multi-contrast imaging and digital refocusing on a mobile microscope with a domed LED array

We demonstrate the design and application of an add-on device for improving the diagnostic and research capabilities of CellScope--a low-cost, smartphone-based point-of-care microscope. We replace the single LED illumination of the original CellScope with a programmable domed LED array. By leveraging recent advances in computational illumination, this new device enables simultaneous multi-contrast imaging with brightfield, darkfield, and phase imaging modes. Further, we scan through illumination angles to capture lightfield datasets, which can be used to recover 3D intensity and phase images without any hardware changes. This digital refocusing procedure can be used for either 3D imaging or software-only focus correction, reducing the need for precise mechanical focusing during field experiments. All acquisition and processing is performed on the mobile phone and controlled through a smartphone application, making the computational microscope compact and portable. Using multiple samples and different objective magnifications, we demonstrate that the performance of our device is comparable to that of a commercial microscope. This unique device platform extends the field imaging capabilities of CellScope, opening up new clinical and research possibilities