Imaging single living cells with a scanning near-field infrared microscope based on a free electron laser

We report the first sub-wavelength mid-infrared images under water, and describe an application to obtaining images of single living cells in water using the Stanford Free Electron Laser (FEL). Spatial resolution is enhanced at the peak of infrared absorption of water. Images were obtained of single motile fibroblasts with the FEL wavelength tuned to absorption peaks of both protein and lipid molecules. Analysis of the unexpectedly strong absorption due to lipid molecules in motile fibroblasts suggests that the concentration of lipid molecules in lamellopodia is consistent with membrane flow. (C) 1998 Elsevier Science B.V. All rights reserved.