(222g) Quantitative Label-Free Interference-Based Phenotyping of Cancer Cells for Liquid Biopsy Applications

Reflection interference contrast microscopy (RICM) is a label-free imaging technique that provides a unique non-invasive “view from below” perspective of micro-scale objects interacting with a surface. RICM’s interferograms embed precise nanometer-scale topographical information about the object under observation, making this microinterferometric approach ideal for phenotypic screening at the single-cell level based on cell adhesion phenomena. In this scenario, employing a large illumination numerical aperture (INA) becomes essential to enhance the contrast of the cell membrane interacting with the surface and produce high quality interferograms. However, important challenges emerge when trying to perform quantitative analysis of such RICM images, due to the lack of sophisticated RICM models that properly interpret intensities as membrane-surface separation distances when using large INAs. Here we present advances that enable quantitative RICM analysis over the full range of possible INAs. We introduce a new model of RICM image formation that successfully accounts for polarization effects, in both liquid and air environments, while facilitating the formulation of an absolute intensity scale. These fundamental advances not only improve quantification of membrane-surface separation but also provide a platform for consistent quantification and characterization of the morphology of the adhesion patch. Such unparalleled capabilities are used here to perform quantitative label-free phenotyping of cancer cells of low (LNCaP) and high (PC3) metastatic potential as they dynamically interact with a glass surface. Our findings illustrate the great potential of this approach for label-free identification of circulating tumor cells (CTCs) in liquid biopsy applications.