Plasmons
In metals, electrons move more freely than in other solids. They sometimes behave like vibrating or oscillating particles, at frequencies similar to those of light, in which case they are referred to as plasmons.

Fluorescent Tags and Detectors
Fluorescent dyes are molecules that absorb light and then emit it at a longer wavelength. The practical effect that we can observe----and that can be detected by various instruments----is that the molecules glow brightly, with a characteristic color.

Fluorescence is quite useful in biotechnology, because they can be used as highly specific tags or probes for molecules of interest. This makes it possible to detect minute quantities of specific biomolecules.

The special properties of plasmons and fluorescent dyes can be harnessed to act as rapid and sensitive detection devices for molecules of biological interest.

Ultrasensitive and rapid detectors can be developed by combining the special properties of metals, plasmons, and fluorescent dyes.