Research Article

Nanohybrids Near-Field Optical Microscopy: From Image Shift to Biosensor Application

Figure 8

(a) left part: SNOM optical image of bare gold plots (sample A), excited at 633 nm. Two hot spots are clearly distinguishable on each plot. Right part: optical profile line of the region under the blue arrow. Signal peaks are separated according to the geometry of sample that is by 1 μm. (b) Near-field topographic image of the bare gold plots (sample A). The double hot spots pattern of (a) is replaced by well separated homogeneous solid ellipsoidal features. (c) Finite Element Simulation of the electric field on the surface of a gold nanoplot. The two red marks at the tips of the ellipsoid refer to the concentrated electric field or hot spots. (d) Simulated absorption spectrum of a gold nanoplot (blue curve); light is longitudinally polarized along the nanoplot major axis. The spectrum is compared with experiment, by Mohamed et al. (red curve). Both curves overlap along the longitudinal surface Plasmon resonance band.