Tomographic refractive index measurement using Adaptive fiber-optical cell Rotation

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Three-dimensional refractive index tomography is an emerging label-free imaging technique that is commonly based on the scanning of the illumination. However, due to the occurring missing cone problem, a low resolutions in the axial direction results. In the first funding period, we demonstrated a multi-core fiber-optic cell rotator (MCF-OCR) system, enabling real-time program-controlled cell rotation about all axes in the dual-beam trap, for the first time worldwide. The MCF-OCR is integrated into a lab-on-a-chip system which can be easily installed in commercially available microscopes due to the high flexibility of optical fibers. It has been proven that MCF-OCR tomography can achieve more precise reconstruction compared to conventional illumination-scanning tomography and providing isotropic resolution in three dimensions. This is valid on the single cell level, but optical tomography of large biological samples like cell clusters, organoids, and embryos remains challenging. In the second phase of the project, we will investigate whether a new dual-beam trap design, together with a tailored version of the Born multiple scattering algorithm enables label-free high-resolution tomography of large biological samples with a diameter larger than 100 microns. The optical trapping stability will be improved by a three-dimensional adaptive trap. The MCF is used for light field imaging to measure the rough refractive index distribution of the cell for generating spatially optimized light fields for the trapping beams. Moreover, applying the rotation of large samples to tomography is also challenging due to the limited depth of field of high-resolution microscopes. Therefore, our experience in adaptive optics will be employed to build an extended depth-of-field microscope for tomography. The aim is to tailor the Born multiple scattering algorithm for tomographic reconstruction from the intensity images. The reconstruction of the high-resolution three-dimensional isotropic refractive index is important for a wide range of applications in biomedicine such as cancer and metabolism studies.