Nanoparticle
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In [[nanotechnology]], a particle is defined as a small object that behaves as a whole unit in terms of its transport and properties. It is further classified according to size: In terms of [[diameter]], fine particles cover a range between 100 and 2500 [[nanometre|nanometers]], while ultrafine particles, on the other hand, are sized between 1 and 100 nanometers. Similarly to ultrafine particles, '''nanoparticles''' are sized between 1 and 100 nanometers, though the size limitation can be restricted to two [[dimensions]]. Nanoparticles may or may not exhibit size-related intensive properties that differ significantly from those observed in fine particles or bulk materials.<ref>[http://www.astm.org/Standards/E2456.htm ASTM E 2456 - 06 Standard Terminology Relating to Nanotechnology]</ref>
[[cluster (physics)|Nanoclusters]]<ref name=Fahlman2007>Fahlman, B. D. ''Materials Chemistry''; Springer: Mount Pleasant, '''MI''', 2007; Vol. 1, pp 282-283.</ref> have at least one dimension between 1 and 10 nanometers and a narrow size distribution. [[powder (substance)|Nanopowders]]<ref name=Fahlman2007>Fahlman, B. D. ''Materials Chemistry''; Springer: Mount Pleasant, '''MI''', 2007; Vol. 1, pp 282-283.</ref> are agglomerates of ultrafine particles, nanoparticles, or nanoclusters.
Nanometer sized [[single crystal]]s, or single-domain ultrafine particles, are often referred to as [[nanocrystal]]s. The term NanoCrystal® is a registered [[trademark]]<ref>See for example US TM Reg. Nos. 2386089 / 2492925 and EU CTM Reg. No. 000885079</ref> of Elan Pharma International (EPIL) used in relation to EPIL’s proprietary milling process and nanoparticulate drug formulations.
Nanoparticle research is currently an area of intense scientific research, due to a wide variety of potential applications in biomedical, optical, and electronic fields. The [[National Nanotechnology Initiative]] has led to generous public funding for nanoparticle research in the [[United States]].
==History==
Although generally nanoparticles are considered an invention of modern science, they actually have a very long history. Specifically, nanoparticles were used by [[artisan]]s as far back as in the 9th century [[Mesopotamia]] for generating a [[glitter]]ing effect on the surface of pottery.
Even these days [[pottery]] from the [[Middle Ages]] and [[Renaissance]] often retain a distinct gold or copper colored metallic glitter. This so called [[lustre]] is caused by a metallic film that was applied to the transparent surface of a [[glazing]]. The lustre can still be visible if the film has resisted atmospheric oxidation and other weathering.
The lustre originates within the film itself, which contains silver and copper nanoparticles, dispersed homogeneously in the glassy matrix of the ceramic glaze. These nanoparticles were created by the artisans by adding [[copper]] and [[silver]] [[salt]]s and [[oxide]]s together
with [[vinegar]], [[ochre]], and [[clay]], on the surface of previously-glazed pottery. The object was then placed to a [[kiln]] and heated to about 600°C in a [[reducing]] atmosphere.
In the heat the glaze would soften, causing the copper and silver [[ion]]s to migrate into the outer layers of the glaze. There the reducing atmosphere reduced the ions back to metals, which then came together forming the nanoparticles that give the colour and optical effects.
Lustre technique shows that craftsmen had a rather sophisticated empirical knowledge of materials. The technique originates in the [[islam]]ic world. As Muslims were not allowed to use gold in artistic representations, they had to find a way to create a similar effect without using real gold. The solution they found was using lustre.
Michael Faraday provided the first description, in scientific terms, of the optical properties of nanometer-scale metals in his classic 1857 paper "Experimental relations of gold (and other metals) to light."<ref>{{cite journal|journal = Phil. Trans. Roy. Soc. London | title = Experimental relations of gold (and other metals) to light | author = Faraday, Michael | volume = 147 |year=1857|pages=145–181 | doi = 10.1098/rstl.1857.0011}}</ref>
Much of the modern day studies of these objects have been conducted at the [[ESRF]] laboratory. Several techniques were used to characterise the chemical and physical properties of these lustre, such as [[Rutherford Backscattering Spectrometry]] (RBS), optical absorption in the visible-[[ultraviolet]] region, [[electron microscopy]] ([[TEM]] and [[Scanning Electron Microscope|SEM]]), [[X-ray diffraction]] and [[X-ray absorption spectroscopy]].<ref>{{cite news|author=Montserrat Capellas Espuny|title=Renaissance Artists Decorated Pottery With Nanoparticles|publisher=[[ESRF]] Newsletter No 38, December 2003|url=http://www.esrf.eu/files/Newsletter/NL38.pdf|accessdate=2007-07-28}}</ref>
==Properties==
[[Image:Nano Si 640x480.jpg|thumb|300px|right|Silicon nanopowder]]
[[Image:nanodiamonds.jpg|thumb|300px|right|Nanodiamonds, TEM image]]
Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and [[atomic]] or [[molecular]] structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale this is often not the case. Size-dependent properties are observed such as [[quantum confinement]] in [[semiconductor]] particles, [[surface plasmon resonance]] in some metal particles and [[superparamagnetism]] in [[magnetic]] materials.
The properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant. For bulk materials larger than one micrometre the percentage of atoms at the surface is minuscule relative to the total number of atoms of the material. The interesting and sometimes unexpected properties of nanoparticles are partly due to the aspects of the surface of the material dominating the properties in lieu of the bulk properties.
Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk [[copper]] (wire, ribbon, etc.) occurs with movement of copper atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are considered super hard materials that do not exhibit the same [[malleability]] and [[ductility]] as bulk copper. The change in properties is not always desirable. Ferroelectric materials smaller than 10 nm can switch their magnetisation direction using room temperature thermal energy, thus making them useless for memory storage. [[suspension (chemistry)|Suspension]]s of nanoparticles are possible because the interaction of the particle surface with the [[solvent]] is strong enough to overcome differences in [[density]], which usually result in a material either sinking or floating in a liquid. Nanoparticles often have unexpected visible properties because they are small enough to confine their electrons and produce quantum effects. For example [[gold]] nanoparticles appear deep red to black in solution.
Nanoparticles have a very high surface area to volume ratio. This provides a tremendous driving force for [[diffusion]], especially at elevated temperatures. [[Sintering]] can take place at lower temperatures, over shorter time scales than for larger particles. This theoretically does not affect the [[density]] of the final product, though flow difficulties and the tendency of nanoparticles to agglomerate complicates matters. The large surface area to volume ratio also reduces the incipient [[melting point depression|melting temperature]] of nanoparticles <ref>{{Citation
| last1 = Buffat | first1 = Ph.
| last2 = Burrel | first2 = J.-P.
| title = Size effect on the melting temperature of gold particles
| journal = Physical Review A
| volume = 13
| issue = 6
| pages = 2287–2298
| year = 1976
| url = http://link.aps.org/abstract/PRA/v13/p2287
| doi = 10.1103/PhysRevA.13.2287 }} </ref>.
Moreover nanoparticles have been found to impart some extra properties to various day to day products. Like the presence of titanium dioxide nanoparticles impart what we call as the self-cleaning effect, and the size being nanorange, the particles cant be seen. Nano Zinc Oxide particles have been found to have superior UV blocking properties compared to its bulk substitute. This is one of the reasons why it is often used in the sunscreen lotions.
Clay nanoparticles when incorporated into polymer matrices increase re-inforcement, leading to stronger plastics, verified by a higher glass transition temperature and other mechanical property tests. These nanoparticles are hard, and impart their properties to the polymer (plastic). Nanoparticles have also been attached to textile fibers in order to create smart and functional clothing.
==Classification==
At the small end of the size range, nanoparticles are often referred to as [[cluster (physics)|cluster]]s. [[Nanospheres]], [[nanorod]]s, and nanocups are just a few of the shapes that have been grown.
[[Metal]], [[dielectric]], and [[semiconductor]] nanoparticles have been formed, as well as [[resonance (chemistry)|hybrid structure]]s (e.g., core-shell nanoparticles). Nanoparticles made of semiconducting material may also be labeled [[quantum dots]] if they are small enough (typically sub 10 nm) that [[quantization]] of electronic [[energy level]]s occurs. Such nanoscale particles are used in biomedical applications as [[drug carrier]]s or [[imaging agent]]s.
Semi-solid and soft nanoparticles have been manufactured. A prototype nanoparticle of semi-solid nature is the [[liposome]]. Various types of [[liposome]] nanoparticles are currently used clinically as delivery systems for anticancer drugs and vaccines.
==Characterization==
Nanoparticle characterization is necessary to establish understanding and control of nanoparticle synthesis and applications. Characterization is done by using a variety of different techniques, mainly drawn from [[materials science]]. Common techniques are [[electron microscopy]] [TEM,SEM], [[atomic force microscopy]] [AFM], [[dynamic light scattering]] [DLS], [[x-ray photoelectron spectroscopy]] [XPS], [[X-ray crystallography|powder x-ray diffractometry]] [XRD], [[FTIR|Fourier transform infrared spectroscopy]] [FTIR], [[MALDI|Matrix-Assisted Laser-Desorption]] [[Time-of-flight mass spectrometry]] [MALDI-TOF], and [[UV-VIs|Ultraviolet-visible spectroscopy]].
Whilst the theory has been known for over a century (see [[Robert Brown]]), the technology for [[Nanoparticle tracking analysis]] (NTA) allows direct tracking of the [[Brownian motion]] and this method therefore allows the sizing of individual nanoparticles in solution.
==Fabrication of nanoparticles==
There are several methods for creating nanoparticles; [[attrition]] and [[pyrolysis]] are common methods. In attrition, macro or micro scale particles are ground in a [[ball mill]], a [[planetary ball mill]], or other size reducing mechanism. The resulting particles are air classified to recover nanoparticles.
In pyrolysis, an organic precursor (liquid or gas) is forced through an orifice at high pressure and burned. The resulting ash is air classified to recover oxide nanoparticle.
A thermal plasma can also deliver the energy necessary to cause evaporation of small micrometre size particles. The thermal plasma temperatures are in the order of 10000 K, so that solid powder easily evaporates. Nanoparticles are formed upon cooling while exiting the plasma region. The main types of the thermal plasmas torches used to produce nanoparticles are dc plasma jet, dc arc plasma and radio frequency (RF) induction plasmas. In the arc plasma reactors, the energy necessary for evaporation and reaction is provided by an electric arc which forms between the anode and the cathode. For example, silica sand can be vaporized with an arc plasma at atmospheric pressure. The resulting mixture of plasma gas and silica vapour can be rapidly cooled by quenching with oxygen, thus ensuring the quality of the fumed silica produced. In RF induction plasma torches, energy coupling to the plasma is accomplished through the electromagnetic field generated by the induction coil. The plasma gas does not come in contact with electrodes, thus eliminating possible sources of contamination and allowing the operation of such plasma torches with a wide range of gases including inert, reducing, oxidizing and other corrosive atmospheres. The working frequency is typically between 200 kHz and 40 MHz. Laboratory units run at power levels in the order of 30-50 kW while the large scale industrial units have been tested at power levels up to 1 MW. As the residence time of the injected feed droplets in the plasma is very short it is important that the droplet sizes are small enough in order to obtain complete evaporation. The RF plasma method has been used to synthesize different nanoparticle materials, for example synthesis of various ceramic nanoparticles such as oxides, carbours/carbides and nitrides of Ti and Si.
Inert-gas aggregation is frequently used to make nanoparticles from metals with low melting points. The metal is vaporized in a vacuum chamber and then supercooled with an inert gas stream. The supercooled metal vapor condenses in to nanometer-sized particles, which can be entrained in the inert gas stream and deposited on a substrate or studied in situ.
==Nanoparticle Morphology==
[[Image:Nanostars.jpg|thumb|left|Nanostars of [[Vanadium(IV) oxide]] ]] Scientists have taken to naming their particles after the real world shapes that they might represent. Nanospheres<ref> Agam and Guo. Electron beam modification of polymer nanospheres. ''Journal of Nanoscience and Nanotechnology'' '''7''' (2007) 3615. JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 7 (10): 3615-3619 OCT 2007 {{doi|10.1166/jnn.2007.814}}</ref>, nanoreefs <ref>Choy JH, Jang ES, Won JH, Chung JH, Jang DJ, and Kim YW. Hydrothermal route to ZnO nanocoral reefs and nanofibers. ''Appl. Phys. Lett.'' '''84''' (2004) 287.</ref>, nanoboxes <ref>Yugang Sun and Younan Xia '''Science''' ''298'' (2002) 2176. {{doi|10.1126/science.1077229}}</ref> and more have appeared in the literature. These morphologies sometimes arise spontaneously as an effect of a templating or directing agent present in the synthesis such as micellular emulsions or anodized alumina pores, or from the innate crystallographic growth patterns of the materials themselves. <ref> Catherine Murphy, ''Science'' '''298''' (2002) 2139.{{doi| 10.1126/science.1080007}}</ref> Some of these morphologies may serve a purpose, such as long [[carbon nanotube]]s being used to bridge an electrical junction, or just a scientific curiosity like the stars shown at left.
== Safety Issues ==
{{seealso|Nanotoxicology |Fine particles}}
Nanoparticles present possible dangers, both medically and environmentally.<ref>Anisa Mnyusiwalla, Abdallah S Daar and Peter A Singer 2003 Nanotechnology 14 R9-R13 doi:10.1088/0957-4484/14/3/201</ref> Most of these are due to the high surface to volume ratio, which can make the particles very reactive or [[catalytic]].<ref>Ying, Jackie. Nanostructured Materials. New York: Academic Press, 2001.</ref> They are also able to pass through [[cell membrane]]s in organisms, and their interactions with biological systems are relatively unknown.<ref>[http://ec.europa.eu/health/opinions2/en/nanotechnologies/l-2/6-health-effects-nanoparticles.htm Nanotechnologies: 6. What are potential harmful effects of nanoparticles?<!-- Bot generated title -->]</ref> However, free nanoparticles in the environment quickly tend to [[wikt:agglomerate|agglomerate]] and thus leave the nano-regime, and nature itself presents many nanoparticles to which organisms on earth may have evolved immunity (such as [[sea salt|salt]] particulates from [[ocean]] [[aerosol]]s, [[terpene]]s from plants, or dust from [[volcano|volcanic]] eruptions){{Fact|date=August 2007}}. A fuller analysis is provided in the article on [[nanotechnology]].
According to the ''[[San Francisco Chronicle]]'', "Animal studies have shown that some nanoparticles can penetrate cells and tissues, move through the body and brain and cause biochemical damage. But whether cosmetics and sunscreens containing nanomaterials pose health risks remains largely unknown, pending completion of long-range studies recently begun by the FDA and other agencies."<ref>{{cite news|author=Keay Davidson|title=FDA urged to limit nanoparticle use in cosmetics and sunscreens|publisher=[[San Francisco Chronicle]]|url=http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2006/05/17/MNGFHIT1161.DTL|accessdate=2007-04-20}}</ref>
Diesel nanoparticles have been found to damage the cardiovascular system in a mouse model.<ref> http://www.bloomberg.com/apps/news?pid=washingtonstory&sid=aBt.yLf.YfOo study Pollution Particles Lead to Higher Heart Attack Risk (Update1)</ref>
==See also==
{{wikibooks|Nanotechnology}}
* [[Liposome]]
* [[Magnetic nanoparticles]]
* [[Nanobiotechnology]]
* [[Nanocrystalline silicon]]
* [[Nanomaterials]]
* [[Nanoparticle Tracking Analysis]]
* [[Nanotechnology]]
* [[Photonic crystal]]
* [[Quantum dot]]
* [[Silver Nano]]
==References==
{{reflist}}
==External links==
* [http://nanoamor.com/products A wide variety of nanoparticles and their dispersions are commercially available] from Nanostructured & Amorphous Materials, Inc.
* [http://www.nano-oxides.com/products.php Nano Particle sized Oxide Powders tested and produced.] by Nano-Oxides, Inc.
* [http://www.liposome.org International Liposome Society]
*[http://people.cornell.edu/pages/jh433/ Textiles Nanotechnology Laboratory] at [[Cornell University]]
* [http://copublications.greenfacts.org/en/nanotechnologies/index.htm#3 Assessing health risks of nanoparticles] summary by [[GreenFacts]] of the European Commission SCENIHR assessment
* [http://www.iop.org/EJ/article/0957-4484/14/3/201/t303R1.pdf?request-id=NENUvFK63BGH-Bna2wi7Kg IOP.org Article]
* [http://books.google.com/books?id=_pbtbJwkj5YC&pg=PA5&lpg=PA5&dq=catalyst+hartog+1972&source=web&ots=fTTD2SA5Dh&sig=3phv63YeG9raeAZdvlm_4JH07-Y#PPR7,M1 Nano Structured Material]
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