Label-Free Single Cell Viability Assay Using Laser Interference Microscopy

SIMPLE SUMMARY: Currently, only a few label-free methods for cell viability assessment are described in the literature. This paper covers a new label-free method based on the laser interference microscopy (LIM) to monitor the viability of single cells in real-time without dye incorporation. The metabolic activity of cells has been a key sign in assessing their viability with use of the LIM-aided method. On this basis, LIM allows the level of cell dynamics to be evaluated. We have analyzed the viability of attached and suspended cells by several spectral techniques of the LIM data processing and selected universal parameters for assessing their condition. Thus, LIM, as a highly sensitive quantitative phase imaging method, is applicable for assessing cell viability by a non-invasive mode combined with other cell assays. ABSTRACT: 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 v(c), this variable determines the viability of a cell only in the attached state (v(c) exceeds 20 nm(2) for viable attached cells). The critical value of the power spectrum slope β(c) 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 β(c) 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 (v(c) and β(c) values) can be used to assay the viability of attached cells.