Quantitative oblique back-illumination microscopy (qOBM) is a label-free imaging technique that enables tomographic phase imaging of thick scattering samples with epi-illumination. Here, we propose the use of two forms of functional imaging with qOBM to study tissue and cell cultures. In doing so, we obtain the spatiotemporal and quantitative functional information associated with the phase values extrapolated from qOBM imaging. We have applied this process to study the efficacy of individual immune T cells to kill glioblastoma spheroid cultures in 3D spheroids. Data show that we can effectively distinguish between cell phenotypes and characterize the dynamic motion of these cells in 3D cultures. This work offers a distinct advantage in tracking 3D cellular dynamics in thick tissue as many function imaging modalities are limited to 2D samples. Further, this technology can be expanded to analyze a wide variety of cellular and subcellular dynamics non-invasively in thick tissue.
Scanning microscopy methods require movement of the focus in Z coordinates to produce an image of a 3-dimensional volume. In a typical imaging system, the optical setup is kept fixed and either the sample or the objective is translated with a mechanical stage driven by a stepper motor or a piezoelectric element. Mechanical Z scanning is precise, but its slow response and vulnerability to mechanical vibrations and stress make it disadvantageous to image dynamic, time-varying samples such as live cell structures. An alternative method less susceptible to these problems is to change the focal plane using conjugate optics. Deformable mirrors, acousto-optics, and electrically tunable lenses have been experimented with to achieve this goal and have attained very fast and precise Z-scanning without physically moving the sample. Here, we present the use of a liquid lens for fast axial scanning. Liquid lenses have a long functional life, high degree of phase shift, and low sensitivity to mechanical stress. They work on the principle of refraction at a liquid-liquid interface. At the boundary of a polar and an apolar liquid a spherical surface is formed whose curvature can be controlled by adjusting its relative wettability using electro-wetting. We characterize the effects of the lens on attainable Z displacement, beam spectral characteristics, and pulse duration as compared with mechanical scanning.
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