Gold that changes colour

01 / WHAT CHANGES

The mechanism

The conduction electrons in a gold nanoparticle can oscillate collectively in response to light: this is localised surface plasmon resonance. Particle size and shape, the medium and aggregation modify absorption and scattering. There is no universal correspondence between a colour and a diameter.

02 / WHERE IT LEADS

An application, in context

This optical sensitivity can be used in sensors: a change in the particle’s surroundings can change the signal. Each system must be designed and calibrated for its intended target.