Real-Time Sensing of Cell Morphology by Infrared Waveguide Spectroscopy

Victor Yashunsky,Benjamin Aroeti,Tal Marciano,Michael Golosovsky,Dan Davidov,Vladislav Lirtsman

doi:10.1371/journal.pone.0048454

Abstract

We demonstrate that a live epithelial cell monolayer can act as a planar waveguide. Our infrared reflectivity measurements show that highly differentiated simple epithelial cells, which maintain tight intercellular connectivity, support efficient waveguiding of the infrared light in the spectral region of 1.4–2.5 µm and 3.5–4 µm. The wavelength and the magnitude of the waveguide mode resonances disclose quantitative dynamic information on cell height and cell-cell connectivity. To demonstrate this we show two experiments. In the first one we trace in real-time the kinetics of the disruption of cell-cell contacts induced by calcium depletion. In the second one we show that cell treatment with the PI3-kinase inhibitor LY294002 results in a progressive decrease in cell height without affecting intercellular connectivity. Our data suggest that infrared waveguide spectroscopy can be used as a novel bio-sensing approach for studying the morphology of epithelial cell sheets in real-time, label-free manner and with high spatial-temporal resolution.

Highlights

Living cells can act as optical devices
We demonstrate that tightly packed live epithelial cell monolayers can guide electromagnetic radiation
The infrared wavelengths are favorable for the waveguide mode excitation in a living cell layer for the following reasons: a) the typical thickness of an epithelial cell monolayer (h,10 mm) is on the order of the infrared wavelength, and b) scattering losses on intracellular compartments are relatively low in that wavelength range [20]

Summary

Introduction

Living cells can act as optical devices. For instance, recent studies have demonstrated single-cell lasing [1] and optical-fiberlike functioning of the Muller retinal cells [2]. In this work we show that a live epithelial cell monolayer can operate as a planar optical waveguide in the infrared spectral region. Several factors conspire to enable the propagation of infrared waveguide modes in cell layers: (i) the ability of cells to self-assemble and form a tightlybound monolayer; (ii) the refractive index of cells is higher than that of the surrounding aqueous media; (iii) the cell height is on the order of the infrared wavelength. We succeeded to excite waveguide modes in different epithelial cell types using prism coupler and collimated infrared light. The waveguide mode excitation is associated with resonant reflectivity minima at certain incident angles. The magnitude and wavelength of these resonances is determined by the intercellular connectivity and cell monolayer thickness (i.e., the average cell height)

Methods

Results

Conclusion