Analysis and Characterization of Manufactured Nanoparticles in Aquatic Environments - Environmental and Human Health Impacts of Nanotechnology - page 210

Depending on the defi nition of colloids or NP used, different requirements are
put on analysis and characterization methods. In reality, it can be seen in literature
that operational defi nitions based on methods are often chosen to defi ne the lower
and upper size limit or other chemical boundaries of colloids. For example, it is
often seen in literature that the colloids in a sample are defi ned as passing a 0.45 µ m

fi lter but being retained by a 1 kDa ultrafi ltration membrane.

6.2 Nanoparticle Analysis and Characterization Methods

This section discusses briefl y why certain nanoparticle characteristics are important
in environmental transport, chemical reactivity and ecotoxicology. This is followed
by a detailed discussion on a suite of applicable analysis and characterization
methods and discussion on their analytical validation and use.

6.2.1 Important Nanoparticle Characteristics

Nanoparticles are often a heterogeneous mixture of particles of different sizes,
shapes, chemical composition, crystal and amorphous structures and with coatings
and surface chemistry. In particular, coatings and surface chemistry can, to some
extent, control their behaviour and, more importantly, often change properties
depending on their surrounding media (Banfi eld and Navrotsky, 2001; Filella, 2007).
Therefore, the view of manufactured NPs as monodisperse, spherical particles
with clean surfaces must be challenged, particularly when present in complex
media such as environmental or biological samples. In Figure 6.1 the complexity
of NPs is illustrated in a multidimensional array of properties, each of which
likely exerts some control of both nanogeochemical and nanoecotoxicological
processes. Consequently, to characterize most of the potentially signifi cant physico-
chemical properties of NPs in environment is challenging from the methodological
point of view. The specifi cations of each of the methods discussed (in Section 6.2.3
to 6.2.8) have been summarized for the respective physico-chemical property in
Table 6.1 .

6.2.1.1 Size and Size Distribution

Nanoparticle size is a governing parameter both for the environmental fate and
behaviour (Gustafsson and Gschwend, 1997; Lead and Wilkinson, 2006) and for the
bioavailability to cells and organisms (Chapter 7 and 9 (this volume); Donaldson
et al. , 2004 ).
Jiang et al. (2008) showed that the cell signalling response was size specifi c with
the highest effect for 40-50 nm. This was consistent with a study of gold nanopar-
ticle uptake by mammalian cells that showed the fastest uptake for 50 nm particles,
compared to both smaller (14 nm) and larger (74 nm) particles (Chithrani et al. ,
2006 ).
Many manufactured NPs exhibit changes in structure and reactivity as a function
of size (atomic clusters- NP -bulk particles). These reactivity changes are often due
to shape, surface defects, crystal edges and corner, porosity, proportion of surface