Fig. 1. (A) Bright-field image of fixed Kit 225 FT7.10 cells labeled with Cy5-conjugated antibodies against IL15R. Bar, 5 µm. (B) Confocal fluorescence image of the same sample area as in A. Bar, 5 µm. (C) NSOM image of the area highlighted in B, and magnified in D, demonstrating the increased spatial resolution and sensitivity of the technique as compared with that of the confocal method. The fluorescence signal on the images is color coded according to the detected polarization, red for 0° channel and green for 90° channel. The arrows in D point to some single-molecule spots. Individual molecules are identified by their unique dipole emission – that is, red and green color-coding. The yellow color of most fluorescent spots results from adding multiple molecules with random in-plane orientation (combination of red and green) in one spot and thus reflects the clustering of receptors on the cell membrane. Bars, 2 µm (C); 1 µm (D).