DNA-Based Self-Assembly

Historically, nanoparticles have been synthesised for their intriguing colours, with one of the most famous examples, the Lycurgus Cup, exhibiting different colours depending upon whether it is illuminated from the inside or the outside. The origin of this phenomenon was unknown at the time and explained only much later on, notably thanks to the development of electron microscopes. The optical properties of the Lycurgus Cup are imparted by the presence of noble metal nanoparticles (composed of a gold–silver alloy) within the glass. With particle sizes typically ranging from 1–100 nanometres, nanoparticles possess electronic properties which are intermediate between the bulk material and their constituent atoms. For metallic nanoparticles, their optical properties are a consequence of their ability to support a localised surface plasmon resonance (LSPR). For example, 10 nm gold spheres are red, while 10 nm silver spheres are yellow. Moreover, the colour depends strongly on the shape, size, material and environment of the particles. Therefore, nanoparticles can exhibit a wide range of colours. Yet, a significantly wider range of optical properties can be accessed via the coupling of the plasmon resonances of particles in close proximity.