Nanomaterials

2. How can nanomaterials be characterised?

• 2.1 Which are the important physical and chemical properties of nanomaterials?
• 2.2 How can nanomaterials detected and analysed?
• 2.3 How are nanomaterials prepared for biological testing?

2.1 Which are the important physical and chemical properties of nanomaterials?

The main parameters which are relevant to the safety of nanoparticles include:

1. Physical properties:

• Their size, shape, specific surface area, and ratio of width and height
• Whether they stick together
• Size distribution
• How smooth or bumpy their surface is
• Structure, including crystal structure and any crystal defects
• How well they dissolve

2. Chemical properties:

• Molecular structure
• Composition, including purity, and known impurities or additives
• Whether it is held in a solid, liquid or gas
• Surface chemistry
• Attraction to water molecules or oils and fats

These parameters should be assessed both for the nanomaterials as they are made, and for nanomaterials as they are used (e.g. in the formulation in any subsequent product). Measurements need to take account of the way properties may change when nanomaterials are mixed with or suspended in other substances.

It is particularly important to measure how quickly nanomaterials dissolve in any liquid they are likely to come in contact with. Their small size means they dissolve faster than the comparable bulk (large) particulate material.

2.2 How can nanomaterials detected and analysed?

The best techniques for tracking nanoparticles depend on where they are. A variety of reliable instruments can identify airborne particles as small as a nanometre across. Electron microscopes can visualise nanoparticles in tissue slices and on the surface of materials. Nanoparticles in suspension in gas or liquids in some solid media can be measured by light scattering and by other microscopic techniques. The standard chemical analysis technique of mass spectroscopy - in which charged particles are separated by size - is applied to nanoparticles suspended in gases and liquids.

All these techniques have their strengths and weaknesses, and they may need to be used in combination. Most still need to be used in the laboratory by experienced technicians, but mobile and even hand-held equipment is becoming available especially for monitoring of air borne nanoparticles.

2.3 How are nanomaterials prepared for biological testing?

Biological testing usually starts with a dry powder or a suspension in water or another liquid which is used to introduce nanoparticles into the organism. There are a range of suggestions for preparations which more closely resemble the way nanoparticles may be spread through a biological system. They include using the common proteins albumin, and fatty substances found in the lining of the lungs. Other possibilities include synthetic detergents, but these complicate assessments of toxicity.