Nanobiotechnology

Nanoscience studies materials at the scale of nanometres (a nanometre is a billionth of a metre): an atom is about 0.1 nm across, a protein or virus tens of nm. Nanomedicine applies it to diagnosing and treating disease.

Small changes everything. When a material is shrunk to the nanoscale, its properties change:

• Gold is yellow in bulk, but particles below 30 nm are ruby red, and up to 100 nm pink.
• Splitting a lump of gold into ever smaller particles multiplies their number and their total surface area, so they become far more reactive.
• Tiny crystals of cadmium selenide, quantum dots, glow in different colours depending on their size.

Kinds of nanoparticles:

• Inorganic: iron oxide, gold, silver, zinc oxide, titanium oxide, silica, calcium phosphate.
• Organic: chitosan, alginate, cellulose, PLA, PLGA, albumin, and liposomes (tiny fat bubbles).
• Carbon: fullerene (C₆₀, a football-shaped molecule), nanotubes and graphene.

Drug delivery. Nanocarriers take a drug to the diseased site, raising its level there while reducing its toxic effects elsewhere (for example, liposomal amphotericin B, an antifungal). The blood vessels of tumours are leaky, so carriers of about 20-30 nm slip out and accumulate in the tumour: the EPR effect (enhanced permeability and retention). Paclitaxel bound to albumin nanoparticles and liposomal doxorubicin are anticancer drugs that use it. Silver nanoparticles fight microbes in wound dressings.

Other uses: zinc oxide and titanium oxide in sunscreens; nano-pesticides and smart food packaging; stain-proof, conductive textiles; tiny nanobiosensors and 'lab-on-a-chip' tests that give results at the bedside.

But the safety of nanoparticles, in the body and in the environment, still needs careful study and regulation.