Nanoscience
How small is "nano"?
is the study of structures in size — roughly a few hundred atoms across. One nanometre (nm) is 1 × 10⁻⁹ m, a billionth of a metre.
| Particle | Diameter |
|---|---|
| 1–100 nm | |
| Fine particles (PM₂.₅) | 100–2500 nm |
| Coarse particles (PM₁₀, e.g. dust) | 2500–10 000 nm |
Nanoparticles are much bigger than single atoms (about 0.1 nm) but far smaller than anything you can see.
Key terms
Surface area to volume ratio
Nanoparticles have a very high . A large share of their atoms are on the surface, where they can react.
For a cube: as the side length decreases by a factor of 10, the SA:V ratio increases by a factor of 10.
Example: a 1 cm cube has SA:V = 6 : 1. A 0.1 cm cube has SA:V = 0.06 : 0.001, or 60 : 1.
This gives nanoparticles different properties from the same substance in bulk. For example, much smaller quantities of a nanoparticle catalyst are needed than of normal-sized particles.
Key terms
Uses and risks
Uses of nanoparticles include:
- medicine — delivering drugs to exactly where they are needed in the body
- electronics
- cosmetics and sun creams — giving better skin coverage and UV protection without leaving white marks
- deodorants — silver nanoparticles kill bacteria
- — the large surface area makes them very effective
However, there are risks. Nanoparticles are so small they can be breathed in and may pass into cells, where they might cause harm. Their long-term effects are not yet fully understood, because they are fairly new. So scientists study them carefully before they are widely used.