105Materials for Nanosensors
In further experiments (Ung et al. 2001), silica-coated gold NPs were pre-
pared in a core–shell structure. The thickness of the silica (SiO
2
) coating was
changed to study its effect. In solution, the position of the SPB was found
to depend on the thickness of the silica coating and therefore separation
between particles.
Then thin lms of silica-coated NPs were deposited on glass substrates.
The colors of these lms were observed to vary with silica thickness, which
determined the interparticle distance. As this distance decreased, the color
of the lm shifted from red to blue. The close distance between the particles
causes dipole–dipole interactions (electrostatic interactions of permanent
dipoles ...