Overview of Nanoscience in the Environment - Environmental and Human Health Impacts of Nanotechnology - page 4

and the Royal Academy of Engineering defi ne nanotechnology as ' the design,
characterization, production and application of structures, devices and systems by
controlling shape and size at the nanometre scale' (Royal Society and Royal
Academy of Engineering, 2004). Nanomaterials are a major component of nano-
technology and can be defi ned as materials that have one or more dimensions in
the range 1-100 nm (Lead and Wilkinson, 2006). Importantly, nanomaterials have
novel properties that differ from those of the same material without nanoscale
features.
A recent attempt to develop a more structured approach has been published by
the British Standards Institution (BSI) (BSI, 2007). In its 'Terminology for nano-
materials' it defi nes nanoscale as the 'size range from approximately 1- 100 nm ' , an
nano - object as a 'discrete piece of material with one or more external dimensions
in the nanoscale' and a nanoparticle as a 'nano-object with all three external dimen-
sions in the nanoscale'. A nanomaterial is a 'material having one or more external
dimensions in the nanoscale or which is nanostructured', with nanostructured being
defi ned as 'possessing a structure comprising contiguous elements with one or more
dimension in the nanoscale' . Defi nitions are also provided for nanorods: ' nano -
object with two similar external dimensions in the nanoscale and the third dimen-
sion signifi cantly larger than the other two external dimensions' ; nanofi bres: 'fl exible
nanorods'; and nanotubes: ' hollow nanorods '. The term high aspect ratio nanopar-
ticles can be used to refer to fi bres, rods or tubes.
These defi nitions are based largely on particle size and do not account for the
issue of particle size distribution satisfactorily or the change in properties as a func-
tion of size. A modifi ed defi nition for a nanomaterial/nanoparticle can be based on
the variation of material properties with size. Other defi nitions are still under dis-
cussion and various relevant bodies, for example, the International Organisation
for Standardisation (ISO), American Society for Testing and Materials (ASTM)
and the Organisation of Economic and Co-operation Development (OECD) are
currently working on precise and formal defi nitions and nomenclature.
The nanoscale dimension in comparison to the known dimensional scale of the
universe is shown in Figure 1.1 (Hochella, 2002). At the smallest end of the scale
(Figure 1.1a) are fundamental particles such as electrons and quarks, which are
smaller than 10 − 18 m, and may approach 10 − 30 m in size or smaller, but such dimen-
sions are not physically measurable at least at this time. At the larger end of the
scale are the size of the Earth (10 7 m in diameter) and the sun (10 9 m in diameter).
The nanoscale with other related objects is described in Figure 1.1b and is in the
range 1-100 nm. A nanometre is a billionth of a metre (i.e. 10 − 9 m). The size of a
single atom is of the order of several angstroms (0.1 nm). The size of a bacterium
is about 1 m (1000 nm), approximately the limit of visibility in light microscopes.

In contrast, 100 nm is approximately equal to the size of a virus. Nanoparticles, like
viruses, cannot be detected through standard light microscopes, because they are
smaller than wavelengths of light (approximately 400- 700 nm). They can be observed
only with higher resolution microscopes such as scanning electron microscope
(SEM, resolution of the order of 10 nm), transmission electron microscope (TEM)
and atomic force microscope (AFM), which both have a resolution of the order of

µ

< 1 nm).