Nanoparticles of less than 100 nanometres in size are used to engineer new materials and nanotechnologies across a variety of sectors. Their small size means these particles have a very high surface area to volume ratio and their properties depend strongly on their size, shape and bound molecules. This offers engineers greater flexibility when designing materials that can be used in our everyday lives. Nanoparticles are found in sunblock creams and cosmetics as well as inside our bodies, as drug delivery vehicles and as contrast agents for pharmaceuticals. Gold nanoparticles are proving to be a next-generation tool in nanoengineering as an effective catalyst at such small dimensions. However, nanomaterials also pose a potential risk, as their interactions with living matter and the environment are not fully understood—meaning that they might not perform as expected, for instance in the human body.