On-chip 3D Microscopy of Optically Cleared Tissue

Low-cost tissue clearing techniques, such as the simplified CLARITY method (SCM), can be used to eliminate the need for precise micro-sectioning of tissue samples and increase the imaging throughput by chemically rendering the tissue transparent while still maintaining the tissue microstructure. However, the mainstream imaging modality for cleared tissue involves fluorescence microscopy, which suffers from limited field of view (FOV), photobleaching and signal fading related drawbacks. Here we present a cost-effective lens-free on-chip microscope for the 3D holographic imaging of tissue samples cleared using SCM and labeled with a colorimetric dye (DAB). We optimized this system by tuning the illumination wavelength, tissue thickness, staining solution, and the number of holograms used for phase retrieval, in order to maintain a high contrast-to-noise ratio while minimizing the amount of acquired data. As a proof of concept, 200 µm-thick mouse brain tissue was successfully imaged over an FOV of 20.5 mm², revealing the 3D distributions of the neurons, which agreed well with a 20X 0.75NA scanning bright-field microscope. The lens-free holographic imaging system also achieved an order of magnitude better data efficiency compared to its lens-based counterpart.