The many colors of gold: from cathedrals to ultrasensitive sensing

Nanotechnology has been introduced as a scientific and technological revolution, which relies on our ability to measure, manipulate and organize matter at the nanometer (10-9 m) scale. In this scale, the properties of materials are different from those we usually observe for the same compounds. Additionally, small variations in size or shape can give rise to significant physical properties and chemical reactivity of the material. The list of applications of Nanotechnology is constantly increasing and starting to make a real impact on our society. A clear example of such a dependence of properties on nanoscale size and shape is the optical response of noble metals, gold being the most characteristic system. Tiny manipulation in the nanoscale morphology of gold particles leads to a full rainbow of bright colors, which are not only beautiful but can also find extremely interesting applications, in a wide variety of fields.