How to get
RI is an intrinsic parameter of any material, describing the speed of light when light passes through the material. The use of RI can be utilized for bioimaging contrast, due to its label-free and quantitative properties. For further information, please see https://www.biorxiv.org/content/early/2017/02/06/106328
Different parts of cellular structures such as cell membrane, cytoplasm, nucleus, and sub-cellular organelles have distinct values of RIs. Thus, the measurements of 3-D RI tomogram of a cell provides a means to visualize 3-D structures of live cells without using staining or labeling-agents.
The principle of the 3-D RI tomogram, or holotomography, is the optical version of X-ray CT. In X-ray CT, X-ray beams with various illumination angles passes through a human body, and the corresponding multiple 2-D X-ray images are obtained, from which 3-D absorption tomogram is obtained via a reconstruction algorithm. In holotomography, laser beams with various illumination angles passes through a live cell, and the corresponding multiple 2-D holographic images are obtained, from which 3-D RI tomogram is obtained via a reconstruction algorithm. Due to the same physical principle, both the X-ray CT and holotomography shares the physical governing equations, cores of reconstruction algorithms, etc.
Phase contrast or Differential interference contrast (DIC) microscopy provides visualization of unstained live cells with high contrast. However, both phase contrast and DIC microscopy only generate 2-D and qualitative imaging. Whereas, Holotomography measures quantitative 3-D tomograms.
Cells are composed of mostly proteins, and cellular body can be understood as a bag of a protein solution. The RI of a protein solution is linearly proportional to the concentration of the solution. Thus, the simultaneous measurement of the volume and the mean RI value of a cell can provide a non-aqueous mass or dry mass of the cell, because the concentration is the ratio of a mass to a volume. For further technical information, please refer to the publication section.
A biological cell is neither a solid or a fluid; it is in-between, or a vixcoelastic material. How stiff or soft a cell is strongly related to its physiological or pathological conditions. TomoCube provides an unique means to measure cellular elasticity of soft cells, such as red blood cells (RBCs), by precisely measuring dynamic fluctuations in cell membrane. Because RBCs are so soft and elastic, they exhibit vibrations in the cell membrane in the order of tens of nanometers, from which cellular elasticity can be assessed. For further technical information, please refer to the publication section.