Carries metallic nanoparticles in blood



Nanoparticles or. Nanoparticles denote a group of a few to a few thousand atoms or molecules. The name comes from their size, which is typically 1 to 100 nanometers. One nanometer equals 10-9 = 0.000000001 meters. The prefix “nano” is derived from the Greek “nanos” for “dwarf” or “dwarfish”.

Nanoparticles can enter the environment naturally (e.g. volcanic eruptions or forest fires) as well as through anthropogenic (man-made) influences (e.g. car and industrial emissions).

Synthetic nanoparticles are artificially produced particles that are specifically equipped with new properties and / or functionalities, such as. B. electrical conductivity, chemical reactivity. Synthetic nanoparticles can be subdivided according to their chemical and physical properties. Groups that are widespread in research and application are:

  • Carbon-containing nanoparticles
  • Metal oxides (silicon dioxide (SiO2), Titanium dioxide (TiO2), Aluminum oxide (Al2O3), Iron oxide (Fe2O3) or (Fe3O4), Zinc oxide (ZnO)
  • Semiconductors (cadmium tellurite (CdTe), silicon)
  • Metals (gold (Au), silver (Ag), iron (Fe))

Carbon-containing nanoparticles can exist in different forms:

While fullerenes and nanotubes are produced synthetically and are therefore clearly defined in their structure (e.g. Buckminster fullerene of 60 carbon atoms), carbon black is understood to mean only very small carbon particles, which are e.g. B. can also arise in combustion processes.
There are many possible areas of application for nanoparticles. So they could z. B. can be used to improve various materials in the household. In medicine, nanoparticles could be used to achieve a targeted transport of drugs in the body or a gentler form of cancer therapy. Nanoparticles could also help in electrical engineering, e.g. B. to enable more powerful and smaller computers. But the military use of nanoparticles is also great. B. be used to develop intelligent weapons.

The high potential benefits result in a drastic increase in the production and use of the most diverse types of nanoparticles, but it also opens up a wide range of possible dangers for us and our environment.
Due to their small size, nanoparticles can be absorbed into the body via the skin, the respiratory tract and the gastrointestinal tract, where they are distributed throughout the entire organism via the bloodstream. The deposition of nanoparticles in certain tissues and organs and their potential ability to form radicals can possibly lead to acute cell and organ damage. Contact with synthetically manufactured nanoparticles occurs either through the use of products containing nanoparticles (such as some sun creams, certain antimicrobial disinfectant sprays, a number of paints and varnishes, etc.) or through exposure during manufacture in the laboratory. This can happen either due to accidents or a lack of safety regulations. The danger of nanoparticles entering nature and thus into food chains currently harbors incalculable risks for all living beings that come into contact with the particles. It is still extremely unclear what effect nanoparticles have on plants and animals and, accordingly, on water, soil and other habitats. However, current studies in this area give reason to assume that the deposition and reactivity of the particles also have a negative effect on exposed organisms.

As a result, much more intensive and, above all, more critical research is necessary so that a responsible handling of nanotechnology and its potential dangers can be made possible.

Nanoecotoxicology was established in order to be able to assess the possible hazards that nanoparticles pose to the environment during their manufacture, use and disposal. It emerged in addition to the ecotoxicology that already existed up to that point, since nanoparticles have novel chemical and physical properties. These require new questions, approaches and procedures for risk assessments.

properties

Nanoparticles have special chemical and physical properties that differ significantly from those of the solid or larger particles. Special features occur, for example, in:

  • the conductivity of the particles,
  • the chemical reactivity that z. B. is used in catalysts: due to the extremely large particle surface compared to the volume, the probability of the interaction of the mobile and solid phase increases.
  • the optical properties of metallic nanoparticles that can absorb light with a specific wavelength. That makes this property z. B. attractive for use in biology and medical diagnostics.

Special nanoparticles

Fullerenes

The fullerenes are brown-black powders with a metallic sheen. They dissolve in some organic solvents (e.g. toluene) with a characteristic color. Fullerenes change from solid to gaseous at approx. 400 ° C.

Carbon nanotubes

Carbon nanotubes consist of cylindrical graphite layers and have a diameter of 1-100 nm. The shape of the nanotubes can be single-walled, multi-walled or Y-shaped. They show, among other things. a high transport speed, a high tear resistance and extreme elasticity, they are also very hard-wearing. They have ten times more tensile strength than steel. [1]Depending on the detail of the structure, the electrical property inside the tube is conductive or semi-conductive.

Carbon black

Graphite (a form of carbon, in addition to diamond and fullerene) is the basic structure of carbon black and a soft, black, metallic, shiny material that occurs both naturally and can be produced artificially. The crystal structure of graphite consists of many parallel layers on top of one another, which can vary in size and arrangement. Within these layers, sp2-hybridized carbon atoms condense to aromatic six-membered rings and form a conjugated π system.

Carbon black is the English name for industrial soot, which is specifically produced under controlled conditions and is physically and chemically defined. On the other hand there is chimney or diesel soot, which is a by-product that is not precisely defined when coal or hydrocarbons are burned. [2][3][4]

Carbon black consists of 96–99% carbon, the remaining parts are hydrogen, oxygen, nitrogen and sulfur, most of which (in functional groups) are chemically bonded to the surface. The surface energy is greatest at the corners and edges of the aromatic compounds, so that adsorption of gases and liquids takes place preferentially. [2][3]

The oxide groups on the pore surface have the greatest influence on the physicochemical properties of carbon blacks, such as water adsorption and catalytic, chemical and electrical reactivity. Mainly, basic hydroxyl, acidic carboxyl as well as carbonyl and lactone groups are formed on the surface. In the production of active carbon blacks, functional oxygen groups can be introduced with a mass fraction of up to 15%.[3]

semiconductor

Semiconductors are solids whose conductivity is temperature-dependent. Electricity is conducted through the movement of electrons. The higher the temperature, the lower the resistance and the higher the conductivity. The conductivity begins approx. When the room temperature is exceeded. Semiconductor nanocrystals are a few nm in size, are powerful, durable and non-toxic [5]

Metals

Compared to previously known orders of magnitude of metals, metallic nanoparticles have changed chemical properties due to their smaller size. B. Gold increases the catalytic effect. In the case of very small gold nanoparticles, the melting point drops drastically. [6] In addition, alkali metal, copper, silver and gold nanoparticles show different optical properties compared to pure metals. In solution, they show a broad absorption band in the visible range of the electromagnetic spectrum and thus have an intense color (characteristic color of colloidal gold: red to purple). [7]

Differentiation from aerosol

Aerosol is the collective name for the finely distributed (dispersed), solid and liquid particles (suspended matter) of different sizes that are floating in gases. The same laws of nature apply to nanoparticles that are suspended in the gas - regardless of whether they were created intentionally or unintentionally.

Manufacturing

Five processes have been established for the production of nanoparticles:

  • Lithography,
  • chemical production in solutions (e.g. Sol-gel method),
  • Production in plasma,
  • Production through self-organized growth on surfaces or with templates (e.g. hydrothermal synthesis of nanoporous cetineites),
  • Production through targeted nucleation of molecules from the gas phase (aerosol process).
  • Electrospinning

Depending on the area of ​​application of the nanoparticles, a precisely defined and narrow particle size distribution is usually required. Depending on the chemical nature of the desired nanoparticles, one or the other method is better suited to achieve a good result. Mostly, methods in solution or methods of self-organization deliver the best results. However, these are difficult or impossible to carry out on an industrial scale.

Uses and benefits of nanoparticles

Nanomaterials

Nanoparticles are already used in the manufacture of many products. Concrete is sometimes mentioned as the oldest nanomaterial, although it was only recognized long after its first use that it owes its strength to crystal structures that are only a few nanometers in size. Whether "marble from the roll", facade plaster that removes pollutants and unpleasant smells by adding nanoparticles, or nanoparticles on roof tiles that are supposed to prevent the growth of algae - there are many ways to improve materials with the help of nanotechnology. [8] A number of cosmetic products, such as various sun creams, deodorants and toothpastes, contain nanoparticles such as titanium dioxide (TiO2) and aluminum oxide (Al2O3), nanoparticles are already being buried in food. In tomato ketchup, silicon oxide is used as a thickener, titanium dioxide is used to lighten salad dressings and aluminum silicate counteracts the clumping of powdered foods. [9] Further examples are nanoparticles in paints and varnishes as well as impregnating agents for all types of surfaces, which are supposed to offer protection against mechanical damage.

Nanoelectronics

It has been possible to create logic circuits from carbon nanotubes and from semiconductor nanocables. These could be the first steps towards making nanocomputers a reality. [10][11] Indium arsenide nanocrystals are used to make light emitting diodes (LEDs). The radiation wavelength is that of telecommunication systems. One area of ​​application could therefore be telecommunications technology.[12] see also: surface chemistry

Military operation

The diverse application possibilities of nanotechnology also open new doors for the military. For example, small, built-in computers in weapons or uniforms would be conceivable - or the use of more powerful computers that would be useful for combat management. It would also be possible to implant nanotechnology in soldiers' bodies for communication, surveillance or drug delivery.[13]

Benefits for the environment

Nanotechnology also offers potential for relieving the burden on the environment, but many of the applications are still in development.

  • Nanomaterials can be used as binders for environmental toxins. For example, two minerals occurring as natural nanoparticles (allophane and a smectite) have been shown to have a high absorption capacity for pollutants such as B. have copper or naphthalene.[14]
  • Nanotechnology-based sensors should be able to be operated very energy-efficiently because of their lower weight. These sensors are primarily developed for the biomedical and military sectors. They can also be used in environmental applications for the optimized and specific detection of biological and chemical contamination.
  • With the use of nanotechnology-based light-emitting diodes (LED), it is said that the energy efficiency for lighting can be increased three to five times compared to lighting with a conventional energy-saving lamp. According to the UBA, the use of dye solar cells promises a higher efficiency of light capture through nanometer-fine distribution of a light-absorbing dye.[15]
  • The water quality can also supposedly be improved. By using nanotechnology-based flow condensers for seawater desalination, over 99 percent of the energy to be applied should be saved compared to conventional reverse osmosis or distillation. In wastewater treatment, pretreated wastewater can be freed of pathogens through nanoporous membranes, thus preventing their spread in the environment.
  • Silicon dioxide and nano-soot particles are already incorporated into modern car tires to reinforce the material. They are supposed to bring about a lower rolling resistance and thus help to save up to ten percent fuel.[15]
  • The cleaning of exhaust gases in motor vehicles is to be improved by using nanoporous filters in order to retain soot particles from exhaust gases.[15]
  • In pest control, ultra-thin nanopolymers could replace toxic organic biocides.
  • By reducing the layer thickness of paints, raw materials can be saved, and it is said that chromium VI paints, which are harmful to the environment and health, can be dispensed with for corrosion protection for metals due to nanotechnology-based surfaces.[15]The use of nanoparticle-containing car paints promises less wear and tear due to the ceramic-like crystalline structure of several wafer-thin layers. According to Mercedes, this nano paint, which has already been in use for two years, still has 72 percent “residual gloss” after around 100 car washes, whereas with conventional paint only 35 percent of the new car brilliance is left with the same load. This paint helps to prevent you from having to wash your car as often, saving water and polluting the groundwater less. According to the manufacturer, there is no health risk because the nanoparticles are bound in a matrix. Similar nano lacquers are also used as wall paint.[16]

Nanomedicine

Nanotechnology opens up a wide field for medical applications.

  • One example is the growth of artificial bones through the implantation of coated titanium frameworks on which the bone component hydroxyapatite can be deposited.[17] In addition, a bone substitute material has been developed which consists of hydroxyapatite. Due to the nanocrystalline structure of the substitute material, bone-forming cells can immigrate and replace the bone substitute mass with natural bones. [18]
  • The special properties of nanomaterials can be used to specifically make the blood-brain barrier passable for therapeutic agents.[15] The targeted introduction of drugs into the body could also be made possible by nanotechnology. The tissue-specific treatment is intended to achieve minimal side effects. The surface quality of the injected substance is decisive for its further targeting in the body. Particles with a water-repellent surface are quickly recognized and eliminated by the immune system. This process can be circumvented by coating the particles with molecules that are not recognized as foreign by the immune system. An example of this is the injection of liposomes (microscopic bubbles made of phospholipids) that have been coated with certain molecules. Liposomes can be used, for example, in cancer therapy, since the blood vessels in tumor cells have greater permeability for the liposomes than the blood vessels in healthy tissues. The liposomes thus accumulate in the tumors. In this way, active ingredients can be used in a targeted manner.[18]
  • For the uptake of substances, cells have a mechanism called receptor-mediated endocytosis (see membrane transport). Here, receptors on the surface of the cells have the function of recognizing substances with suitable surface molecules and initiating the uptake of the substance into the cell. The receptors vary from cell type to cell type or from tissue to tissue. If the desired substance is coated with biomolecules, such as. B.Monoclonal antibodies (see antibodies) or sugar residues - which can have highly specific properties and can therefore only be recognized by certain cell receptors - it is possible to direct the substance into a very specific body tissue.[19]
  • Cancer treatment with iron oxide nanoparticles is another research area (see nanotechnology).

Possible risks

The enormous reactivity of nanoparticles and the drastic increase in the production and use of the most varied types of nanoparticles open up a broad spectrum of possible dangers for humans and the environment. According to the manufacturer, none of the products poses a health or ecological hazard, but this claim is not tenable with current knowledge of the chemical and physical behavior of nanoparticles, especially with regard to ecological systems. The expansion of the product range for the benefit of the consumer can bring great advantages, but the advantages and disadvantages of the nanotechnologies already used and the materials used must be carefully weighed.[20] Numerous studies have already shown possible environmentally damaging and health-damaging aspects of nanotechnologies, for example the absorption of the particles into the organism via the respiratory tract, skin and mouth, even in products such as cosmetics and food additives that are already on the market.

Risks to humans

By consuming and using products containing nanoparticles, people come into contact with these potentially harmful substances. If the particles are absorbed into the organism, they can cause considerable damage there and become the cause of diseases. In addition, there is a risk of exposure during the production of nanoparticles, as the lack of risk research also means that the rules for safety at work in laboratories are insufficient. Due to their small size (10–100 nm), nanoparticles can be absorbed into the body via the skin, the respiratory tract and the gastrointestinal tract, where they are distributed throughout the entire organism via the bloodstream.

  • When using nano impregnation sprays, for example, nanoparticles can be absorbed into the lungs through the air we breathe. In the lungs, nanoparticles reach the area of ​​the alveoli, in contrast to larger particles. There they become the trigger for severe inflammation of the lung tissue. In addition, the transfer of the particles into the bloodstream also takes place at this point.[21] Smaller particles pass more easily into the blood and can then penetrate the blood-brain barrier.[15][22]
  • Basically, it has been shown that nanoparticles that are absorbed through the olfactory mucous membrane reach the brain via the nerve tracts of the olfactory bulb and through the extremely selective blood-brain barrier. [23] The protection of the brain from highly reactive and presumably tissue-damaging substances is therefore no longer guaranteed due to the size of the nanoparticles.
  • As a result of the uptake of nanoparticles, especially in people suffering from arteriosclerosis and heart disease, the existing disease can worsen and there can be deposits in various organs such as the spleen, liver, bone marrow, etc.[23]
  • The consumption of foods that contain nanoparticles enables the potentially harmful substances to be absorbed into the bloodstream via the mucous membranes of the gastrointestinal tract. In the intestine, nanoparticles are absorbed by Peyer's plaques. When nanoparticles are absorbed via the gastrointestinal tract, the smaller the particles, the greater the likelihood that the absorbed particles will be deposited in certain tissues and organs and that they will be damaged.[23]
  • Another possibility for the absorption of nanoparticles into the organism is possibly via the skin, e.g. B. by the direct application of nanoparticle-containing cosmetics.[23] Some studies refute the uptake of nanoparticles up to living cell layers of the epithelial tissue; other studies give indications to the contrary. Nanoparticles contained in cosmetic products can be absorbed directly into the skin via the cornea or via hair roots and cause damage to the cells there due to the formation of radicals and possibly trigger skin irritations and allergies. In the organism there is a risk that the particles will disrupt mitochondrial respiration and thus the cell metabolism. However, the exact effect has not yet been adequately researched, which is why it seems very threatening that numerous skin care products already contain nanoparticles.[21][22]

Risks to the environment

It is not clear whether these ecological risks and dangers also apply to nanoparticles introduced into carrier substances (paints, facade paints, textiles) or technical devices (information technology). The current state of science does not allow any reliable statements to be made about the danger and harmfulness to health with regard to nanoscale ingredients and components. It still needs to be clarified whether, due to certain weather conditions or mechanical stress, nanoparticles can escape from facade paints, car tires or paints in the form of nanoscale abrasion.

If nanoscale particles are washed out from solid carrier substances, a burden on humans and the environment is to be expected here as well.

The use of nanoscale compounds is very likely synonymous with their entry into the environment or their entry into food chains and, as a result, damage to ecological systems. Even if the nanomaterials as such do not cause any direct damage, nanoparticles could, due to their high reactivity, bind other pollutants and facilitate their transport in the air or in water. This would result in an increased burden on the environment and organisms.[20]

The behavior of nanoparticles in the air is discussed in more detail under Dangers during manufacture. In water, too, particles can fundamentally change their properties by binding other substances, so that, for example, the absorption of nanoparticles in organisms would be facilitated. Either the nanoparticles themselves or the pollutants bound to them could trigger negative effects in the organisms.[20]

If the nanoparticles ingested or used by humans through food, cosmetics, etc. are excreted or released, they end up in the water and soil via the wastewater. Groundwater remediation with the help of special nanoparticles can also result in high soil pollution. There is a risk that the nanoparticles will be absorbed by animals and plants and thus enter the food chain.[20]

A study by Ling Yang and Daniel J. Watts from the New Jersey Institute of Technology provides information on the negative or inhibitory effects of nanoparticles on the growth of roots in plants.[24]

Due to these disturbing research results, it is imperative to clarify whether and in what form nanomaterials can enter the environment during the manufacturing process, when a product is used, through aging and degradation, and through disposal and recycling. The Federal Ministry for the Environment (BMU) sees its task in protecting the environment and health. According to an article by the BMU, however, considerations about the disposal of nanoparticles are still marked with a question mark. [25]

The biological activity of the nanoparticles depends on the size, shape, chemistry, surface and solubility of the particles. The hazard potential is mainly due to the binding to and from toxic substances, the mobilization of heavy metals, binding of nutrients in the groundwater, accumulation via the food chain, worldwide distribution via the air and changes in the microfauna due to biocidal effects in soil and water.[26]

When creating disposal guidelines, one should primarily clarify whether the particles are free or bound to a matrix, whether they are water-soluble or not, whether they disintegrate or aggregate. There is no such thing as “the nanoparticle”, each substance has to be considered individually and for this purpose the different particles have to be characterized and standardized.[26] Despite inadequate disposal guidelines, or rather: despite the complete lack of disposal guidelines (according to unconfirmed sources, some companies should simply throw their nano-waste into the wastewater!), Research is already underway, often neglecting environmentally harmful aspects. According to the Federal Ministry of Research, Germany is currently at the forefront of nanoresearch in Europe with 290 million euros in public funding annually. The EU provides a total of 740 million euros in public money.[27]

  • Studies with fish indicate that nanoparticles can also penetrate biological barriers such as the blood-brain barrier. The so-called C60 molecules (also known as “Buckminster fullerenes”) are absorbed through the gills at relatively low concentrations. The distribution of the nanoparticles in the body seems to be dependent on size, shape and material properties.[22]

Manufacturing Risks

When manufacturing nanoparticles, there is a risk of people being exposed at their workplace, because the knowledge about the actual behavior of nanoscale substances is so poor that it is not possible to establish meaningful MAK or TRK values ​​to a satisfactory extent. This ignorance of the general chemical and physical properties of particles of this size and also the lack of ethical examination of this area will possibly lead to the "accidental" production of highly dangerous substances that cause great damage to exposed organisms.

Faults in the apparatus can cause nanoparticles to be released into the environment during their synthesis. Such an accident is much more difficult to determine than with larger particles because the concentrations in which nanoparticles are present are usually very low. Nanoparticles move very quickly and can travel long distances in the air. They are distributed in the room in a very short time, so that not only areas in the immediate vicinity are contaminated, but also areas and people further away. Highly sensitive gas detection systems are necessary for control.[20]

At the moment there are neither suitable masks nor high-performance filters available that offer sufficient protection to directly exposed people.[21] Although nanoparticles are subject to a rapid growth process due to collision and agglomeration, the aggregated particles are mostly still nanoparticles.[20]

In the near future, production will be followed by long-distance transport of nanoparticles. Accidents, such as a leaking or sinking oil tanker, transferred to nanoparticles, currently possibly catastrophes of unpredictable proportions.

The production of large quantities of substances such as nanoparticles must result in a targeted disposal management and policy with particular attention to the chemistry and reactivity of the material to be disposed of. In addition, safety standards both during manufacture and during transport must be based on the hazard potential of the substances in question. This is not possible with regard to nanoparticles, since the range of products is already much larger than the range of the investigated nanoparticles.

Individual evidence

  1. Paschen, H., Coenen, C., Fleischer, T., Grünwald, R., Oertel, D., Revermann, C .; Nanotechnology - research, development, application; Springer-Verlag; Berlin, Heidelberg, New York 2004
  2. ab Donnet, J.B .; Bansal, R.C .; Wang, M.-J .: Carbon Black - Science and Technology, second edition, Marcel Dekker, New York - Basel - Hong Kong 1993
  3. abc Bansal, R. C .; Donnet, J.-B .; Stoeckli, F.: Active Carbons, Marcel Dekker, New York and Basel 1988
  4. Degussa: Pigments Series, No. 47
  5. Atkins, P.W., Beran, J.A .; Chemistry - everything; VCH Verlagsgesellschaft mbH; Weinheim, New York, Chichester, Brisbane, Singapore, Toronto 998
  6. Schmid, G .; Corain, B.: Eur. J. Inorg. Chem., 2003, 3081-3098
  7. Left.; Wang, Z.L .; El-Sayed, A.: J. Phys. Chem. B, 1999, 103, 3529-3533
  8. Nanomaterials
  9. Borowski, A .: Mini-Particles in Food - Red Milk and Pizza Multi. Link: [www.sueddeutsche.de/wissen/artikel/369/90279/] 2006
  10. Bachtold, A., Hadley, P., Nakanishi and T., Dekker, D .: Logic Circuits with Carbon Nanotube Transistors. Science 294: 1317-1320, 2001
  11. Huang, Y., Duan, X., Cui, Y., Lauhon, L. J., Kim, K. H., Lieber, C. M .: Logic Gates and Computation from Assembled Nanowire Building Blocks. Science 294: 1313-1317, 2001
  12. Tessler, N., Medvedev, V., Kazes, M., Kan, S., Banin, U .: Efficient Near-Infrared Polymer Nanocrystal Light-Emitting Diodes. Science 295: 1506-1508, 2002
  13. Altmann, J .: Military use of nanotechnology: limitation is necessary. Berlin, Academic Publishing Society, 2006
  14. Yuan, G .: Natural and modified nanomaterials as sorbents of environmental contaminants. In: Journal of Environmental Science and Health 2004, 39:2661–2670
  15. abcdef Federal Environment Office: Nanotechnology: opportunities and risks for people and the environment, 2006
  16. Brinkmann M .: Tomorrow's car paint - high-tech in the skin. In: Spiegel online 2005
  17. Silva, G. A .: Introduction to Nanotechnology and Its Applications to Medicine. In: Surgical Neurology 61:216–20, 2004
  18. ab Wagner, V., Zweck, A .: Nanomedicine - Innovation Potential in Hessen for Medical Technology and the Pharmaceutical Industry. Hessian Ministry for Economy, Transport and State Development, 2006
  19. Davis, S. S .: Biomedical applications of nanotechnology - implications for drug targeting and gene therapy. In: Trends in Biotechnology 15 (6): 217-24, 1997
  20. abcdef Krug, F.H .: Effects of nanotechnological developments on the environment. UWSF 4, 223-230, 2005
  21. abc Peter, P .: Environmental and health risks of nanotechnological applications. Natural and Social Science Interface.
  22. abc Oberdörster et al .: Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles, 2005
  23. abcd Roblegg, E., Sinner, F., Zimmer, A .: Health risks of nanotechnology. nanoGesund. 2006
  24. Watts, D.J., Yang, L .: Particle surface characteristics may play an important role in phytotoxicity of alumina nanoparticles. In: Toxicology Letters 158, 122-132, 2005
  25. http://www.dialog-nanopartikel.de/
  26. ab M. Rappolder: Nanotechnology: Small Particles - Big Effects, Dessau 2006
  27. G. Samulat: Noted! From the weal and woe of the dwarf world

literature

Books

  • H. Haberland: Clusters of Atoms and Molecules I., Jumper, 52, 1994
  • H. Haberland: Clusters of Atoms and Molecules II, Jumper, 56, 1994
  • C.F. Drilling, D.R. Huffman: Absorption and Scattering of Light by Small Particles, Wiley, 1983
  • U. Kreibig, M. Vollmer: Optical Properties of Metal Clusters, Springer, 1995

Essays

  • Harald F. Krug: Effects of nanotechnological developments on the environment. Environmental sciences and pollutant research 17 (4), pp. 223-230 (2005), ISSN 0934-3504
  • Petra Schaper-Rikel: Governance of promises for the future: On the political economy of nanotechnology POKLA issue 145, 36 (2006) 4, 473-496.