Optical imaging of cell mass and growth dynamics

Abstract

Using novel interferometric quantitative phase microscopy methods, we demonstrate that the surface integral of the optical phase associated with live cells is invariant to cell water content. Thus, we provide an entirely noninvasive method to measure the nonaqueous content or "dry mass" of living cells. Given the extremely high stability of the interferometric microscope and the femtogram sensitivity of the method to changes in cellular dry mass, this new technique is not only ideal for quantifying cell growth but also reveals spatially resolved cellular and subcellular dynamics of living cells over many decades in a temporal scale. Specifically, we present quantitative histograms of individual cell mass characterizing the hypertrophic effect of high glucose in a mesangial cell model. In addition, we show that in an epithelial cell model observed for long periods of time, the mean squared displacement data reveal specific information about cellular and subcellular dynamics at various characteristic length and time scales. Overall, this study shows that interferometeric quantitative phase microscopy represents a noninvasive optical assay for monitoring cell growth, characterizing cellular motility, and investigating the subcellular motions of living cells. phase microscopy; interferometric microscopy; cell growth PHASE-CONTRAST (PC) and differential interference contrast (DIC) microscopy have been used extensively to study live cells without the need for exogenous contrast agents (32). The tremendous success of these methods is due to the fact that the optical phase shift through a given sample contains information about the refractive index (n) variations that directly result from structural features within the sample. Refractive index n can therefore be regarded as a powerful endogenous contrast agent for cellular structure (6). However, as the relationship between the irradiance and phase of the image field is generally nonlinear (30, 39), both PC and DIC are qualitative in nature and limited to morphological observations without specific structural data.Quantitative phase microscopy has received substantial interest in recent years, as quantifying optical phase shifts associated with cells provides structural and dynamical information at the nanometer scale without the need for any cell preparation or the use of exogenous contrast or labels. Existing methods for biological quantitative phase measurements can be divided into single-point and full-field techniques. Several point measurement techniques have been used for investigating the local structure and dynamics of live cells (1,7,10,14,29,36,37). In contrast, full-field phase measurement techniques provide simultaneous information from a large region of the sample, which offers the additional benefit of studying both the temporal and spatial behavior of the sample (2, 5, 9, 13, 18 -20, 40, 41).Over the past several years, our laboratory has developed new full-field phase imaging techniques that are suitable for spatially resolved investigation of live cell...

Quantitative Phase Imaging for Label-Free Analysis of Cancer Cells—Focus on Digital Holographic Microscopy

“…The ability to measure cell count was validated for the first time in 2008 by Mölder et al [21], using human breast and prostate cancer cell lines, as well as a mouse fibroblast cell line. Measurement of cell growth has been well documented for both adherent and non-adherent cells [8,9,15,[25][26][27][28]47,49,56,59,61]. By segmentation of cellular outlines, morphology and motility can also be studied [7,50,51,57,80].…”

Real time blood testing using quantitative phase imaging

“…The underlying principle of the microscope is quantitative phase imaging [19], in which we retrieve the optical pathlength map associated with the blood film. Because the optical pathlength (or phase) contains information about both the sample refractive index and thickness, QPI has been used to provide measurements of red blood cell volumes [20], cell dry mass [21,22,23,24,25], dynamics [26,27,28,29,30,31], cell tomography [32,33,34,35], tissue scattering [36,37,38]. QPI has attracted increasing scientific interest in the past decade especially because it can study structure and dynamics quantitatively, with nanoscale sensitivity, and without the need for labeling with contrast agents.…”

Scanning color optical tomography (SCOT)

“…The refractive index is the source of image contrast in DHM, which can be related to the average concentration of non-aqueous contents within the specimen, the socalled dry mass [1][2][3]. Tomographic interrogation of living biological specimens using DHM can thereby provide the mass of cellular organelles [4] as well as three-dimensional morphology of the subcellular structures within cells and small organisms [5].…”