As-Produced Intrinsic Physico-Chemical Properties and Appropriate Characterization Tools - Safety of Nanomaterials along Their Lifecycle - page 13

NOAAs are mainly Auger electron spectroscopy, XPS, and SIMS (described in
Figure 1.8).
It has been widely reported that surface chemistry can play one of the key roles in
determining the hazard of any given NOAA. Several studies have shown that NOAAs
of the same material but with different surface chemistry have different properties
with respect to cell uptake and toxicological profile (Goodman et al. 2004; Chithrani
et al. 2006; Walkey et al. 2011; Suresh et al. 2012).

1.8 SURFACE CHARGE
Surface charge influences the state of nanomaterial agglomeration and the
adsorption of ions and biomolecules onto a nano-object's surface. Consequently,
it can affect cell uptake of the nano-object and its biodistribution (e.g., Limbach
et al. 2007; Limbach et al. 2009; Lockman et al. 2004). The toxicological role of
surface charge has been deeply discussed by Oberdörster et al. (2005) and Nel
et al. (2006).
Surface charge of a nano-object can be determined by zeta potential measure-
ments. These measurements involve quantifying the velocity of particle movement
in an applied electric field. The zeta potential is a function of the surface charge of
the particle, adsorbed species on its surface, and composition and ionic strength of
the surrounding solution. Hence, the zeta potential values alone do not provide much
information and it is important to report additionally the other abiotic factors such
as temperature, pH, and ionic strength of an analyzed sample. Zeta potential of an
NOAA is normally measured by light-scattering electrophoresis or electroacousto-
phoresis methods. The theory used for zeta potential calculation should be noted
(e.g., Smoluchowski, Huckel, Henry, and others) and the limitations of these theories
should be recognized. The isoelectric point (IEP) (pH where the zeta potential is
equal to zero) of a material under controlled conditions should be reported together
with the zeta potential values (Figure 1.9).

5.0

-5.0

1.0 3.0 5.0 7.0 9.0 11.0

-15.0

-25.0

-35.0

-45.0

pH

FIGURE 1.9 Zeta potential and isoelectric point of silica nanoparticles (NanoGEM.SiO 2 .
FITC).