Toxicological Effects of Metal Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 190

constitutes an integral part of many consumer products, ranging from cosmetics,
cleaning disinfectants to sport textiles. Moreover, nanosilver has found widespread
use in medical products, such as adhesive tape, wound dressings as well as medical
instruments. The antimicrobial behavior of nanosilver is derived from its interac-
tion with bacterial proteins resulting in enzyme inactivation or protein denaturation.
However, this effect does not seem to be restricted to microorganisms because silver
nanoparticles can also bind to free thiol groups of cysteines and sulfhydryl groups of
proteins in mammalian cells (Chen et al. 2008).
Gold nanomaterials can be easily synthesized in multifaceted shapes, with variant
sizes and different surface modifications. Apart from colloidal gold, gold nanoshells,
nanorods, and nanowires are the most popular. Engineered gold nanoparticles dis-
play excellent absorbance and scattering of light making them very useful for bio-
medical applications like medical imaging, biological diagnostics, and biosensorics.
In recent years, gold nanoparticles have also been tested in in vivo models for drug
therapy as well as in rheumatoid arthritis and hyperthermia treatment for tumor
destruction (Khlebtsov and Dykman 2010).
In contrast to silver and gold nanoparticles, copper nanoparticles are predomi-
nantly present in industrial applications; for example, as additives for lubricant
oil, metallic coatings and inks, and lithium ion batteries, as well as polymers and
plastics. Nanosized copper particles were also listed as skin product components in
the US Woodrow Wilson database of nanotechnology-based products (http://www.
nanotechproject.org/cpi/products). This might raise concerns because copper has
strong cytotoxic effects mediated at least in part by binding to sulfur-based polypep-
tides thereby leading to protein denaturation (Jeon, Jeong, and Jue 2000; Cecconi
et al. 2002).
Due to their high conductance and reactivity which is strongly enhanced in nano-
sized materials, platinum nanoparticles are employed in many industrial products and
processes, for example, as catalysts for fuel cells. In addition, platinum nanoparticles
are also announced as supplements in some cosmetics and personal care products
in the United States, advertising their antioxidative potential and protective effect
against reactive oxygen species (http://www.nanotechproject.org/cpi/products).
The wide range of applications and the intended use of metal-based nanopar-
ticles in personal care products pose the risk of human exposure in environmental,
occupational, and consumer settings. Consequently, the possible hazards associated
with exposure to these nanomaterials have to be carefully evaluated on the basis of
toxicological investigations. With regard to metal nanoparticles, the largest number
of toxicological studies have been conducted using silver and gold nanoparticles,
whereas relatively few studies were devoted to copper or platinum nanoparticles.
Recent reviews summarize the toxicity of nanosilver or nanogold (Johnston et al.
2010; Khlebtsov and Dykman 2011; Pan, Bartneck, and Jahnen-Dechent 2012; Reidy
et al. 2013; Schäfer et al. 2013). As already pointed out in Chapter 8, the toxic poten-
tial of nanoparticles cannot always be extrapolated from the toxicity of the corre-
sponding bulk material. The unique properties that drive the exploitation of metal
nanoparticles in industry might also entail unpredictable effects of these materials
on cells and organs. This emphasizes the need for a thorough understanding of the
correlative relationship between the nanoparticles' physicochemical properties and