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We studied the effect of the interaction of electromagnetic radiation with human keratinocytes (HaCaT), at low (50 Hz, 1 mT) frequency using both atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) techniques. AFM analysis showed modifications in shape and morphology in exposed cells, while SNOM indirect immunofluorescence analysis revealed an increase of segregation of β4 integrin (an adhesion marker) in the cell membrane of the same cells, suggesting that a higher percentage of the exposed cells shows a modified pattern of this adhesion marker.

The morphological changes of murine hematopoietic 32D Cl3-A cell line, in which apoptosis was induced by deprivation of interleukin-3 (IL-3) from the culture medium, were studied through air operating atomic force microscopy. The subtraction of IL-3 determines the appearing of blebs on plasma membrane and cell fragmentation in several residual bodies. Areas of strong contrast in the friction images, which are nearly absent in control and necrotic cells, were detected with percentage that peaks at 6 h of IL-3 deprivation. These are the results revealing that transient modification of the plasma membrane accompanies the first steps of apoptosis pathway.

First experiments at the Vanderbilt free electron lasers measured the local reflectivity of a PtSi/Si system. The reflectivity in the scanning near-field optical microscope images revealed features that were not present in the corresponding shear-force (topology) images and which were due to localized changes in the bulk properties of the sample. The size of the smallest detected features clearly demonstrated that near-field conditions were reached. The use of different photon wavelengths (0.653, 1.2, and 2.4 mu m) enabled us to probe regions of different depth. (C) 1998 American Institute of Physics.