1. From solid gold to nanometric gold

One of the characteristics of nanoscience is that new properties emerge when the size of an object falls below a "boundary" of a few tens of nanometers. This may come as a surprise, because intuitively, we tend to think that the "whole" must replicate the properties of its constituent parts. But it is precisely this intuition that nanoscience seems to be disproving. Gold nanoparticles (NPs) provide a good illustration of the emergence of new properties as we move towards nanometric scales. Before going into more detail, this paragraph highlights three factors that cause these unexpected properties to emerge from the nanoscale: electromagnetic confinement, the predominance of surface effects and, finally, quantum effects. The body of the article will describe these properties in greater depth and illustrate them with applications.