1 millimetre = 1 million nanometres

Nanoparticles are found in nature - in soot and volcanic ash but it now possible to make nanoparticles from many different elements and control the shape of the particles made. Their usefulness lies in their extremely small size and their relatively large surface area, which can make them very chemically reactive. Pure metal nanoparticles can be exlposive and find application as rocket propellents.The characteristics and properties we associate with bulk metals such as colour, reflectivity, melting point change for their nanoparticle counterparts and once created they have a natural tendency to aggregate together strongly and particularly clever chemistry and processing is required to render them useful. Many long chain molecules will attach themselves to nanoparticles and self assemble as if by magic so they surround the nanoparticles in monolayers.

By controlling the chemistry of these attached molecules, many useful properties can be engineered particularly in medicine where targeted drug delivery is required and the dispersive properties of the nanoparticles can also be controlled. Nanoparticles from gold and silver were made first and once created these have the advantage that they resist oxidation though they are expensive but other metal nanoparticles will oxidize readily and the extent of this oxidation has to be limited to retain their chemical reactivity. Stabilizing molecules are used which self assemble onto the newly created nanoparticles and prevent oxidation. Nanoparticles are roughly 1/100th the size of a human cell and cover a size range from a few nanometers to a few hundred nanometres and it is difficult to conceive how small they are.

Because they are so small, nanoparticles can only be seen with powerful electron microscopes and the smallest particles are really only clusters of atoms. Hundreds of new uses for nanoparticles are discovered every week and the technology is growing exponentially. Providing we can optimise the very clever chemistry required to make these particles useful and easy to process they represent a new class of material with truly quantum properties and realistically anything will be possible in the future using them. My involvement with nanoparticles was to research how copper nanoparticles might be engineered to formulate an ink capable of being used in an inkjet printer to print electronic circuits on polymer substrates. Such inks using silver had already been made but were horrendously expensive so a cheaper metal was desirable. This application makes use of the much lower melting point of metal nanoparticles allowing them to form continuous electrically conductive tracks by heating (sintering using high intensity flash lights) to temperatures only a little higher than the boiling temperatiure of water.