Nanoscale devices are one hundred to ten thousand times smaller than human cells. They are similar in size to large biological molecules ("biomolecules") such as enzymes and receptors. As an example, haemoglobin, the molecule that carries oxygen in red blood cells, is approximately 5 nano meters in diameter. Nanoscale devices smaller than 50 nano meters can easily enter most cells, while those smaller than 20 nano meters can move out of blood vessels as they circulate through the body. Because of their small size, nanoscale devices can readily interact with biomolecules on both the surface and inside cells. By gaining access to so many areas of the body, they have the potential to detect disease and deliver treatment in ways unimagined before now.