nanoparticle
Meaning of nanoparticle: Small enough that surface area dominates behavior, which is why the same material acts differently once broken this fine.
Definition of nanoparticle
A nanoparticle is a piece of material smaller than about 100 nanometers across, roughly a thousandth of the width of a human hair. At that size a substance behaves differently from the same substance in bulk, because so much of it lies at the surface. Medicine uses nanoparticles to carry drugs, imaging dyes and antibodies to chosen tissues.
Why does size change what a material does?
Break a solid into ever smaller pieces and the share of its atoms sitting on the surface climbs steeply. Since chemistry happens at surfaces, a material that is inert as a lump can be highly reactive as a powder of nanoparticles. Optical behavior shifts too. Gold in bulk is yellow, while gold nanoparticles scatter light as red or purple depending on their diameter, an effect used in stained glass long before anyone understood why. Magnetic behavior and melting point change over the same size range.
What are they used for in medicine?
| Use | How it works |
|---|---|
| Drug carriage | The drug rides inside or on the particle and is released where it lands |
| Contrast for scanning | Iron oxide or gold particles alter what the scanner sees |
| Vaccines | Fatty particles protect genetic material and deliver it into cells |
| Targeting | Antibodies fixed to the surface steer the particle toward one cell type |
Carrying a drug this way changes where it goes and how long it lasts. Nanoparticle paclitaxel, in which the drug is bound to the blood protein albumin, was developed to avoid the solvent the original formulation needed and the reactions that solvent caused.
How do they reach a tumor?
Blood vessels grown by tumors are hastily built and leaky, and tumor tissue drains poorly, so particles of the right size tend to seep out and linger there. That tendency underlies much of the interest in nanoparticles for cancer, although it varies enormously between tumors and has proved far less dependable in people than in laboratory animals. Attaching a targeting antibody helps a particle stay once it arrives, but it does not by itself get the particle out of the bloodstream. The same leakiness is used in imaging, where it makes a tumor stand out.
What are the concerns?
Particles this small can enter cells and cross barriers larger material cannot, which is the point in medicine and the worry in industry. Inhaled nanoparticles reach the deepest parts of the lung. Where the body cannot break a particle down, it may persist in the liver, spleen or lymph nodes for a long time. Safety therefore has to be judged for each material, size and surface coating separately, because the behavior of the bulk substance is a poor guide.
Used in a sentence
The contrast agent used iron oxide nanoparticles taken up by cells of the reticuloendothelial system.
Good to know
What a nanoparticle does depends on its material, size and surface coating rather than on the bulk substance it is made from, so behavior and safety have to be established separately for each formulation.
Word origin
Where “nanoparticle” comes from
Nano comes from the Greek nanos, meaning dwarf, and marks a billionth part in the metric system.