IR Guided Modes


Waveguide mode in live cell epithelia

We demonstrate that a live epithelial cell monolayer can act as a planar waveguide, see reference. Our infrared reflectivity measurements show that highly differentiated simple epithelial cells, which maintain tight intercellular connectivity, support efficient propagation of the waveguide modes in the spectral region of 1.4-2.5 µm and 3.5-4 µm. Disruption of cell-cell contacts by calcium depletion abolishes propagation of the waveguide modes, whereas calcium replenishment restores them. The resonant wavelength and magnitude of the waveguide resonances discloses quantitative dynamic information on cell height and cell-cell connectivity. In particular, we show that cell treatment with the PI3-kinase inhibitor LY294002 results in a progressive decrease in cell height without affecting intercellular connectivity. Thus, 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. 


Schematic representation of intracellular leaky waveguide mode propagation in a living cell monolayer. A| Waveguide mode excitation in a living cell monolayer. An electromagnetic wave penetrates at an incident angle θinc from the high-refractive-index substrate into a cell monolayer having a lower refractive index, ncell,. Because nmedium is lower than ncellthis wave undergoes total internal reflection at the cell-medium interface.  The wave then impinges on the cell-substrate interface where it is partially reflected (solid red arrow) and refracted (pale red arrow). Excitation of the radiative (leaky) waveguide mode occurs when the reflected and refracted waves at the substrate-cell interface interfere destructively, confining the energy within the cell layer. B| XZ-section of epithelial MDCK cell monolayer stably expressing LifeAct-GFP as imaged by confocal microscopy. Scale bars: 10 µm. 

References
Yashunsky V, Marciano T, Lirtsman V, Golosovsky M, Davidov D, et al. (2012) Real-Time Sensing of Cell Morphology by Infrared Waveguide Spectroscopy. PLoS ONE 7(10): e48454



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