Quantitative phase imaging (QPI) provides a label free method for imaging live cells and allows quantitative estimates of cell volume. Because the phase of light is not directly measurable at an imaging sensor, QPI techniques involve both hardware and software steps to reconstruct the phase. Digital holographic microscopy (DHM) is a QPI technique that utilizes an interferometer to combine a reference beam with a beam that passes through a specimen. This produces an interference pattern on the image sensor, and the specimen’s phase can be reconstructed using diffraction algorithms. One limitation of DHM is that the images are subject to coherent diffraction artifacts. Transport of intensity (TIE) method, on the other hand, uses the fact that defocused images of a specimen depend on the specimen’s phase to determine the phase from two or more defocused images. Its benefit over DHM is that it is compatible with conventional bright field imaging using sources of relatively low coherence. Although QPI methods can be compared on a variety of static phase targets, these largely consist of phase steps rather than the phase gradients present across cells. In order to compare the QPI methods described above on live cells, rapid switching between QPI modalities is required. We present results comparing DHM and TIE on a custom-built microscope system that allows both techniques to be used on the same cells in rapid succession, which allows the comparison of the accuracy of both measurements.
Iron is an essential element required for human life, and is highly regulated in the body. Iron deficiency leads to many adverse health effects, such as anemias. The exact mechanisms of iron release in cells are not well known. We developed a Raman micro-spectroscopy technique that allows detection of transferrin (Tf) bound iron inside intact human cells. Ferric iron (Fe3+) bound to serum Tf is internalized into cells via the transferrin receptor (TfR). Methods that allow determining when and where Tf releases iron inside a cell lead to a better understanding of disease progression, including cancer. We have previously shown that Raman micro-spectroscopy is able to detect and quantify the Tf-bound iron in human breast cancer T47D cells. In this work, we applied hyperspectral Raman imaging to visualize the spatial distribution of Tf-bound iron in human breast cancer T47D and MDAMB231 cells internalized with iron-loaded Tf. We have also shown that Raman imaging can quantify the amount of iron under different times of Tf internalization prior to fixation. Raman microspectroscopy provides a unique way to determine the amount of iron under different Tf internalization times by employing the Raman metric, which was used to quantify iron content in iron bound Tf (holo-Tf) samples. Importantly, Raman microspectroscopy can be used to follow iron release from Tf in breast cancer cells. Determining the kinetics and location of iron release in cancer cells is key to further our understanding of iron metabolism during cancer progression.
Repair or reconstruction of organs is the goal of regenerative medicine. Bioengineered organoids that can differentiate when implanted in-vivo to partially restore organ function are being developed. Potentially, such organoids can be used to treat many medical conditions. A non-invasive method for quality monitoring of tissue engineered constructs is needed in order to ensure that they are ready for implantation. Raman micro-spectroscopy offers a way to quantitatively analyze cells and tissues without sample preparation or labelling dyes, which are not allowed in constructs used for the human implantation. Epithelial progenitor cells are parts of the complex organoids derived from the embryonic salivary gland cells. We have collected Raman spectra of the epithelial (acinar and ductal) cells treated with Fibroblast Growth Factor 2 (FGF2) and grown in organoids ex vivo over a period of (1 - 7 days). Evolution of the organoids over time was detected with Raman. These modifications, corresponding to the C-C stretch and C-H bend in proteins, as well as alterations in the Amide I and III envelopes, likely may correlate with changes in the cell environment or their differentiation state. Our goal is to develop Raman metrics that can be applied to the non-invasive monitoring of organoids.
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