| Summary: | Laser interference microscopy (LIM) is a promising label-free method for single-cell research applicable to cell viability assessment in the studies of mammalian cells. This paper describes the development of a sensitive and reproducible method for assessing cell viability using LIM. The method, based on associated signal processing techniques, has been developed as a result of real-time investigation in phase thickness fluctuations of viable and non-viable MCF-7 cells, reflecting the presence and absence of their metabolic activity. As evinced by the values of the variable <i>v<sub>c</sub></i>, this variable determines the viability of a cell only in the attached state (<i>v<sub>c</sub></i> exceeds 20 nm<sup>2</sup> for viable attached cells). The critical value of the power spectrum slope <i>β<sub>c</sub></i> of the phase thickness fluctuations equals 1.00 for attached MCF-7 cells and 0.71 for suspended cells. The slope of the phase fluctuations’ power spectrum for MCF-7 cells was determined to exceed the threshold value of <i>β<sub>c</sub></i> for a living cell, otherwise the cell is dead. The results evince the power spectrum slope as the most appropriate indicator of cell viability, while the integrated evaluation criterion (<i>v<sub>c</sub></i> and <i>β<sub>c</sub></i> values) can be used to assay the viability of attached cells.
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