Contrary to the belief of many, nanotechnology is not a new concept. Nano-materials have always existed: For example, nano sized particles are formed by gas-phase atmospheric reactions, volcanic eruptions or recombination in sediments. Human generated nano-sized particles have occurred since the fumes from the first man-made fire. In the recent years, two things have however changed: public awareness for the special properties of nano-materials has arisen and the technology to specifically design materials at the nano-scale level has developed [Scenihr 06].
Compared to larger particles, nano particles (NP) have unique physical-chemical properties. Their surface to mass ratio is extremely high and the nano-scale quantum confinement effects may affect the characteristics of the clusters or particles [Kurath & Maasen 06, Oberdorster et al. 05B]. Interactions with cells and sub-cellular structures are therefore likely to be different from those observed for larger particles [Oberdöster et al. 05A]. These special and today unpredictable attributes are reasons for the attractiveness of nanotechnology; but also constitute a potential toxicological risk for mankind and the environment. The environmental regulations and occupational health guidelines concerning particulate matter have not yet been fully adapted to the special properties for these materials and it is still debatable whether they need to be [Maynard et al. 06].
When entirely new potential risk materials are identified an extensive analysis of their toxicological properties is necessary. Proper population-risk assessment and safety analysis can only be implemented at this basis, so we may enjoy the full benefits of nanotechnology while avoiding the downfalls [Scenihr 06, Shields 06]. The following is an overview of the key areas related to the toxicology of NP and metallic atomic quantum clusters (AQC) in the present study.
The precise definitions of the terms “AQC” and “NP” are still being debated [Kurath & Maasen 06]. Thus, in this thesis AQC are defined as monodisperse atom clusters consisting of 2 to 50 atoms, approximately 0.3 nm to 1.4 nm in diameter [Kuo & Clancy 05]. NP are defined as homogeneous mono-disperse particles with at least two dimensions in the range of 50 atoms to 100 nm. Particles of polydisperse and chemically complex nature less than 100 nm in all three dimensions are considered ultra fine particles [Kurath & Maasen 06, Oberdorster et al. 05B]. Nano scale particles (NSP) is used as a collective term that includes AQC, NP and ultra fine particles.
Metallic atomic quantum clusters
AQC, by some also called “nano-clusters”, are a new promising material type in the field of nanotechnology. AQC are atom aggregations too small to be considered particles. Recently, it has been confirmed that specific types of AQC suspended in water or an organic solvent can be stable at -20 to +20 ºC for several weeks [Kou & Claucy 05, López del Río T (NanoGap), personal correspondence]. Coupled with the unique optical, electrical, and magnetic properties of NP, this stability can be exploited in a diversity of applications, such as catalysts, fuel cells and biosensors [NanoGap 07].