Gold nanoparticles

Gold nanoparticles (NPs) are among the most studied and widely used structures in nanoscience and nanotechnology. We can list a number of advantages that make them virtually indispensable. First, gold NPs are fairly easy to synthesize and do not require complex storage conditions.

Furthermore, even though each NP is invisible under a conventional optical microscope, as it measures only a few nanometers, a group of NPs colors an aqueous solution with a characteristic ruby-red color, which allows for easy initial diagnosis of their presence. They have thus found unique medical and pharmaceutical applications.

This ruby red color is the macroscopic manifestation of a nanometric resonance phenomenon called plasmon resonance. This resonance is the third advantage of gold NPs because it transforms them into nano-antennas and nano-radiators.

A fourth advantage of gold is its chemical stability, which makes it an unalterable metal that is very difficult to oxidize. This is why it is classified as a noble metal. This remains true at the nanometric scale, and gold therefore remains metallic at this scale. Other metals, on the other hand, oxidize, and the oxide layer alters the nanoparticles throughout their volume. This particular feature has led to the development of gold NP chemistry.

In this context, however, gold NPs surprised researchers working in the field of catalysis, as they proved to be highly reactive in certain chemical reactions. In the 1990s, this opened up a whole new field of gold catalysis, which is largely responsible for the current enthusiasm for gold NPs.

It is also this chemical stability that justifies the use of gold in electronics, to create stable contacts. However, today, gold NPs reveal specific electronic properties linked to their nanometric size, whether as nanoelectrodes to establish contacts with single molecules, or as a kind of nanocomponent to study quantum conduction phenomena.

Finally, since the first discoveries by researchers in the 1990s, many topics have been addressed, and in the 2020s, we are now in the era of technological and even commercial applications. This article discusses the fundamental properties of gold nanoparticles and describes how to synthesize them for specific applications. It also briefly presents their applications. [NM 902] and [NM 904] discuss advances based on gold nanoparticles in nanoelectronics and nanomedicine.