We all know what gold looks like: yellow and solid. However, gold nanoparticles (GNPs) are quite different: invisible to the eye, changing colour and often contained in liquid. GNPs have different sizes ranging from a few nanometres to a few hundreds, and present distinct forms like spherical, triangles, irregular shapes and many more.

Gold nanoparticles have been used since a long time by artists due to the vibrant colours produced by their interaction with visible light. More recently, GNPs have been used in technology applications such as organic photovoltaics, for the targeted delivery and controlled release of therapeutic agents, in electronic conductors, and catalysis. Their importance in the field of health and nanomedicine is growing over time as GNPs show promising results and a large variety of applications. The optical and electronic properties of gold nanoparticles are tuneable by changing the size, shape, surface chemistry, or aggregation state. For example, by changing the size and concentration of GNPs in a solution the colour of the solution changes.

Suspension with different sizes and concentrations of GNPs

Generally, to prepare gold nanoparticles, a wet chemical method is used. For example, gold ions can react with citrate ions to form gold particles. An acid solution containing a gold salt is mixed with sodium citrate that, through a redox reaction (electron transfer reaction), produces gold particles. Sodium citrate acts both as the reducing agent (agent that transfer electrons) and stabilizer, preventing the gold particles from agglomerating. Nevertheless, many other synthesis methods exist depending on the type of gold nanoparticles shape or size desired and its final application.

Within the nTRACK project, two types of gold nanoparticles are being developed. One type is made of gold only, while others have an iron oxide core, are coated with gold and their surface is functionalized with glucose. The gold only particles have the advantage of fulfilling Good Manufacturing Practices (GMP) standards but are not compatible with Magnetic Resonance Imaging (MRI). The gold nanoparticles with an iron oxide core have the advantage that it acts as contrast agent in magnetic resonance, whereas the gold layer can be used as contrast agent by computed tomography but they are not fulfilling GMP requirements yet. The glucose coating aims to facilitate the uptake of the nanoparticles by the stem cell membrane. Below a graphical representation of the nTRACK GNPs.

For more information about the nTRACK GNPs, you can read our poster:

Last, it is important to mention that GNPs have a wide application in the health sector and are crucial in many processes. For instance, GNPs are used as a contrast agent for theragnostic to develop personalized treatments. In this case, the molecular imaging enables the characterization of biological processes at the cellular and molecular levels. Furthermore, GNPs or more precisely nanorods are used to produce a hyperthermia effect on tumour cells in order to kill them. Moreover, GNPs are used in biosensors for their electrical and optical properties as they can increase the sensitivity of the device or in rapid test (e.g. pregnancy tests or detection of antibodies test (including COVID)).

For further information about GNPs, we recommend the two following videos: