What’s so Special about Nanotechnology?
Not much!! The word “nano” refers to a length scale. A nanometer is one billionth of a meter – that’s about 10,000 times smaller than the thickness of a human hair. Every solid and liquid has a nanostructure!!! “Nano” only matters when that length scale gives a material some particular property or can allow a particular application that is not seen at other length scales. All living systems are really skilled at controlling nanosized structures within each of their cells and have been successfully doing so since all life began. What is special is that we have now learnt to make and study materials at this nanoscale, albeit not as exquisitely as Nature does.
What is a nanoparticle?
There is a scientifically agreed definition of a nanoparticle, which often gets abused by many companies when they promote their products as being “nano”. The strict scientific definition of nanoparticles is “A material containing particles where at least 50 % of the particles have at least one dimension in the size range 1 nm – 100 nm”. Nanoparticles are currently being intensely developed, due to a wide variety of potential applications, mainly in biomedical, optical, electronic and materials fields. The use of nanotechnology in agriculture is really still in its infancy. In spite of the hype promoted by some Agtech companies, products with average particle sizes greater than 100 nm are NOT nanoproducts.
How stable are nanoparticle suspensions?
The special properties of nanoparticles come from their small size. One of those properties is a very high surface area for a given mass. Some can have the area of over a tennis court in just one gram of the material. That surface area has a much higher energy than in the interior of the particle, which makes nanoparticle inherently unstable – the particles want to minimise the total energy contained in surface of the material. So the simplest way of doing that is to join the nanoparticles together into much larger agglomerates. In fact, it is very difficult to keep them apart as single nanoparticles, unless we specially modify their surfaces. Statements made, such as, “suspension nanoproducts with reduced particle sizing have improved shelf life, as the particles within the product stay in suspension for longer” are just not correct! The smaller the particle size, the more likely they are to aggregate into bigger lumps.
What use are nanoparticles in agriculture?
Nanostructured suspensions do have specific advantages. If the nanoparticle of a micronutrient element is really small on average (say 30 nm) it can behave similarly to that element in soluble form in the soil and may also release the micronutrient to be taken up in the leaf or by the roots. The big advantage is that we can chemically modify surface properties of this very large surface area nanomaterial, so we can also change its behaviour and mode of delivery in ways we cannot do with soluble micronutrients.
What is the future of nanomaterials in agriculture?
With the appropriate nanoparticle surface properties, achieved by changing the surface charge or by grafting bulky organic polymers onto that very high area surface, there is considerable promise towards improving long-term stability of high analysis suspensions. We now have the ability to rationally design nanoparticle properties, to create more controlled release of the micronutrient over an extended period of time, or to deliver at the same time, specific bioactive groups, such as fungicides or plant growth hormones grafted onto the nanoparticle surface. These advantages have derived from our initial ability to modify nanoparticle high surface areas to prevent agglomeration as a result of their small size.