Particle size is one of the most important parameters not only
for description of fundamental properties of materials, but also
within the biological systems as it can affect a number of key
features and processes, such as drug targeting, delivery or
distribution. Regarding nanosized particles, ISO standard ISO/TS
27687:2008 (ISO, 2008) provides their definition as an object with
a size between 1 and 100 nm. In the EU, the respective Commission
Recommendation (EC, 2011) defines a “nanomaterial” to be a
“natural, incidental or manufactured material containing particles,
in an unbound state or as an aggregate or as an agglomerate and
where, for 50% or more of the particles in the number size
distribution, one or more external dimensions is in the size range
1–100 nm”.