Tomocube

Refractive index (RI) is a fundamental optical property that measures how much light is bent as it enters a material. It indicates the speed of light in a given medium compared to its speed in a vacuum. This property is determined by the material's optical density and molecular structure.

RI finds applications in various fields, including bioimaging, where its label-free and quantitative properties are particularly valuable. RI-based imaging techniques offer detailed insights into biological samples' structure and composition without the need for external labels or dyes. This makes them highly useful in biomedical research and diagnostics, providing high-resolution and sensitive imaging capabilities for studying cellular morphology, composition, and dynamics.

Phase contrast and Differential Interference Contrast (DIC) microscopy are widely used techniques for visualizing unstained live cells with high contrast. However, both phase contrast and DIC microscopy offer only 2D qualitative imaging.

Holotomography (HT), on the other hand, provides quantitative 3D tomograms. This means it not only captures the structural details of the sample but also allows for precise measurements of various parameters within the sample volume. Unlike phase contrast and DIC microscopy, which rely on contrast enhancements, HT directly measures the refractive index variations within the sample, enabling detailed three-dimensional reconstructions. This quantitative aspect of HT makes it particularly valuable for studying dynamic biological processes and understanding cellular structures in greater detail.

Holotomography (HT), analyzed using software like TomoAnalysis, provides a wealth of information across multiple parameters. These include morphological, chemical, and mechanical aspects of the imaged samples.

Morphological Parameters: HT enables the measurement of various morphological parameters such as volume, surface area, projection area, and sphericity. These parameters offer insights into the shape and size characteristics of the imaged objects.

Chemical Parameters: Through holotomographic analysis, chemical information such as dry mass and concentration can be determined. For example, in the case of red blood cells, hemoglobin concentration can also be measured, providing valuable biochemical insights.

Mechanical Parameters: HT facilitates the measurement of mechanical properties such as cell stiffness. This parameter offers crucial information about the mechanical behavior and integrity of the imaged samples, which can be particularly relevant in studying cellular biomechanics and response to external stimuli.

Cellular dry mass refers to the mass of cellular material excluding water content. Cells are primarily composed of proteins, resembling a protein solution enclosed within a membrane. The refractive index (RI) of a protein solution correlates linearly with its concentration.

By simultaneously measuring a cell's volume and mean RI value, researchers can calculate its non-aqueous mass or dry mass. This calculation exploits the relationship between concentration, mass, and volume.