We present a time-multiplexing structured illumination control technique for optical diffraction tomography (ODT). Instead of tilting the angle of illumination, time-multiplexed sinusoidal illumination is exploited using a digital micromirror device (DMD). The present method effectively eliminates unwanted diffracted beams from binary DMD patterns, which deteriorates the image quality of the ODT in the previous binary Lee hologram method. We experimentally show the feasibility and advantage of the present method by reconstructing three-dimensional refractive index distributions of various samples and comparing with a conventional Lee hologram method.
Microalgae are promising candidates for biofuel production due to their high lipid content. To facilitate utilization of the microalgae for biofuel, rapid quantification of the lipid contents in microalgae is necessary. However, conventional methods based on the chemical extraction of lipids require a time-consuming destructive extraction process. Here, we demonstrate label-free, non-invasive, rapid quantification of the lipid contents in individual micro-algal cells measuring the three-dimensional refractive index tomograms. We measure three-dimensional refractive index distributions within Nannochloropsis oculata cells and find that lipid droplets are identifiable in tomograms by their high refractive index. In addition, we alter N. oculata under nitrogen deficiency by measuring the volume, lipid weight, and dry cell weight of individual cells. Characterization of individual cells allows correlative analysis between the lipid content and size of individual cells.
Cancer stem cells (CSCs) are a subset of tumor cells, which are characterized by resistance against chemotherapy and environmental stress, and are known to cause tumor relapse after therapy. A number of molecular mechanisms underlie the chemoresistance of CSCs, including high expression levels of drug efflux transporters. We investigated the role of the antioxidant transcription factor NF-E2-related factor 2 (NRF2) in chemoresistance development, using a CSC-enriched colonosphere system. HCT116 colonospheres were more resistant to doxorubicin-induced cell death and expressed higher levels of drug efflux transporters such as P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) compared to HCT116 monolayers. Notably, levels of NRF2 and expression of its target genes were substantially elevated in colonospheres, and these increases were linked to doxorubicin resistance. When NRF2 expression was silenced in colonospheres, Pgp and BCRP expression was downregulated, and doxorubicin resistance was diminished. Collectively, these results indicate that NRF2 activation contributes to chemoresistance acquisition in CSC-enriched colonospheres through the upregulation of drug efflux transporters.
Simultaneous imaging of various facets of intact biological systems across multiple spatiotemporal scales would be an invaluable tool in biomedicine. However, conventional imaging modalities have stark tradeoffs precluding the fulfilment of all functional requirements.Here we propose the refractive index (RI), an intrinsic quantity governing light-matter interaction, as a means for such measurement. We show that major endogenous subcellular structures, which are conventionally accessed via exogenous fluorescence labeling, are encoded in 3D RI tomograms. We decode this information in a data-driven manner, thereby achieving multiplexed microtomography. This approach inherits the advantages of both highspecificity fluorescence imaging and label-free RI imaging. The performance, reliability, and scalability of this technology have been extensively characterized, and its application within single-cell profiling at unprecedented scales has been demonstrated..
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