Nanotech, Drug Delivery, CNT

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Nanotechnology

Nanotechnology, shortened to "nanotech", isthe study of the controlling of matter on anatomicandmolecularscale. Generally

nanotechnology deals with structures of the size100nanometersor smaller in at least onedimension, and involves developing materials ordevices within that size. Nanotechnology is verydiverse, ranging from extensions ofconventionaldevice physicsto completely newapproaches based uponmolecular self-assembly, from developingnew materialswithdimensions on the nanoscale to investigatingwhether we candirectly control matter on the

atomic scale.

There has been much debate on the futureimplications of nanotechnology.Nanotechnology has the potential to createmany new materials and devices with a vastrange ofapplications, such as inmedicine,electronicsand energy production. On the otherhand, nanotechnology raises many of the sameissues as with any introduction of newtechnology, including concerns about the

toxicityand environmental impact ofnanomaterials,[1]and their potential effects onglobal economics, as well as speculation aboutvariousdoomsday scenarios. These concernshave led to a debate among advocacy groupsand governments on whether specialregulationof nanotechnologyis warranted.

Origins:

The first use of the concepts found in 'nano-technology' (but pre-dating use of that name)was in "There's Plenty of Room at the Bottom,"a talk given by physicistRichard Feynmanat anAmerican Physical Societymeeting atCaltechonDecember 29, 1959. Feynman described a

process by which the ability to manipulateindividual atoms and molecules might bedeveloped, using one set of precise tools tobuild and operate another proportionallysmaller set, and so on down to the neededscale. In the course of this, he noted, scaling

issues would arise from the changing magnitudeof various physical phenomena: gravity wouldbecome less important, surface tension andvander Waals attractionwould become increasinglymore significant, etc. This basic idea appearedplausible, and exponential assembly enhances itwithparallelismto produce a useful quantity ofend products. The term "nanotechnology" wasdefined byTokyo Science UniversityProfessorNorio Taniguchiin a 1974 paper[2]as follows:

"'Nano-technology' mainly consists of theprocessing of, separation, consolidation, anddeformation of materials by one atom or by onemolecule." In the 1980s the basic idea of thisdefinition was explored in much more depth byDr. K. Eric Drexler, who promoted thetechnological significance of nano-scalephenomena and devices through speeches andthe booksEngines of Creation: The Coming Eraof Nanotechnology(1986) and Nanosystems:Molecular Machinery, Manufacturing, and

Computation,[3]and so the term acquired itscurrent sense.Engines of Creation: The ComingEra of Nanotechnologyis considered the firstbook on the topic of nanotechnology.Nanotechnology and nanoscience got started inthe early 1980s with two major developments;the birth ofclusterscience and the invention ofthescanning tunneling microscope(STM). Thisdevelopment led to the discovery offullerenesin 1985 andcarbon nanotubesa few years later.

In another development, the synthesis andproperties of semiconductornanocrystalswasstudied; this led to a fast increasing number ofmetal and metal oxide nanoparticles andquantum dots. Theatomic force microscope(AFM or SFM) was invented six years after theSTM was invented. In 2000, the United StatesNational Nanotechnology Initiative was founded
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otshttp://en.wikipedia.org/wiki/Quantum_dotshttp://en.wikipedia.org/wiki/Atomic_force_microscopehttp://en.wikipedia.org/wiki/Atomic_force_microscopehttp://en.wikipedia.org/wiki/Atomic_force_microscopehttp://en.wikipedia.org/wiki/Atomic_force_microscopehttp://en.wikipedia.org/wiki/Quantum_dotshttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Carbon_nanotubeshttp://en.wikipedia.org/wiki/Fullereneshttp://en.wikipedia.org/wiki/Scanning_tunneling_microscopehttp://en.wikipedia.org/wiki/Cluster_(physics)http://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Nanotechnology#cite_note-2http://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Engines_of_Creation:_The_Coming_Era_of_Nanotechnologyhttp://en.wikipedia.org/wiki/Eric_Drexlerhttp://en.wikipedia.org/wiki/Nanotechnology#cite_note-1http://en.wikipedia.org/wiki/Norio_Taniguchihttp://en.wikipedia.org/wiki/Tokyo_Science_Universityhttp://en.wikipedia.org/wiki/Parallelismhttp://en.wikipedia.org/wiki/Van_der_Waals_forcehttp://en.wikipedia.org/wiki/Van_der_Waals_forcehttp://en.wikipedia.org/wiki/Van_der_Waals_forcehttp://en.wikipedia.org/wiki/Caltechhttp://en.wikipedia.org/wiki/American_Physical_Societyhttp://en.wikipedia.org/wiki/Richard_Feynmanhttp://en.wikipedia.org/wiki/There%27s_Plenty_of_Room_at_the_Bottomhttp://en.wikipedia.org/wiki/Regulation_of_nanotechnologyhttp://en.wikipedia.org/wiki/Regulation_of_nanotechnologyhttp://en.wikipedia.org/wiki/Regulation_of_nanotechnologyhttp://en.wikipedia.org/wiki/Grey_goohttp://en.wikipedia.org/wiki/Nanotechnology#cite_note-0http://en.wikipedia.org/wiki/Nanotoxicologyhttp://en.wikipedia.org/wiki/Nanoelectronicshttp://en.wikipedia.org/wiki/Nanomedicinehttp://en.wikipedia.org/wiki/List_of_nanotechnology_applicationshttp://en.wikipedia.org/wiki/Implications_of_nanotechnologyhttp://en.wikipedia.org/wiki/Molecular_nanotechnologyhttp://en.wikipedia.org/wiki/Molecular_nanotechnologyhttp://en.wikipedia.org/wiki/Molecular_nanotechnologyhttp://en.wikipedia.org/wiki/Nanomaterialshttp://en.wikipedia.org/wiki/Molecular_self-assemblyhttp://en.wikipedia.org/wiki/Molecular_self-assemblyhttp://en.wikipedia.org/wiki/Semiconductor_devicehttp://en.wikipedia.org/wiki/Nanometerhttp://en.wikipedia.org/wiki/Molecularhttp://en.wikipedia.org/wiki/Atomic


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to coordinate Federal nanotechnology researchand development.

Fundamental concepts

One nanometer (nm) is one billionth, or 109, ofa meter. By comparison, typical carbon-carbonbond lengths, or the spacing between theseatoms in a molecule, are in the range 0.120.15nm, and aDNAdouble-helix has a diameteraround 2 nm. On the other hand, the smallestcellularlife-forms, the bacteria of the genusMycoplasma, are around 200 nm in length.

To put that scale in another context, thecomparative size of a nanometer to a meter isthe same as that of a marble to the size of theearth. Or another way of putting it: ananometer is the amount a man's beard growsin the time it takes him to raise the razor to hisface. Two main approaches are used innanotechnology. In the "bottom-up" approach,materials and devices are built frommolecularcomponents whichassemble themselves

chemically by principles ofmolecularrecognition. In the "top-down" approach, nano-objects are constructed from larger entitieswithout atomic-level control.

Areas of physics such asnanoelectronics,nanomechanicsandnanophotonicshaveevolved during the last few decades to providea basic scientific foundation of nanotechnology.

Simple to complex: a molecularperspective

Modernsynthetic chemistryhas reached thepoint where it is possible to prepare smallmoleculesto almost any structure. Thesemethods are used today to manufacture a widevariety of useful chemicals such as

pharmaceuticalsor commercialpolymers. Thisability raises the question of extending this kindof control to the next-larger level, seekingmethods to assemble these single moleculesintosupramolecular assembliesconsisting ofmany molecules arranged in a well defined

manner.

These approaches utilize the concepts ofmolecular self-assemblyand/orsupramolecularchemistryto automatically arrange themselvesinto some useful conformation through abottom-upapproach. The concept ofmolecularrecognitionis especially important: moleculescan be designed so that a specific configurationor arrangement is favored due tonon-covalent

intermolecular forces. The WatsonCrickbasepairingrules are a direct result of this, as isthe specificity of anenzymebeing targeted to asinglesubstrate, or the specificfolding of theproteinitself. Thus, two or more componentscan be designed to be complementary andmutually attractive so that they make a morecomplex and useful whole.

Such bottom-up approaches should be capableof producing devices in parallel and be much

cheaper than top-down methods, but couldpotentially be overwhelmed as the size andcomplexity of the desired assembly increases.Most useful structures require complex andthermodynamically unlikely arrangements ofatoms. Nevertheless, there are many examplesof self-assembly based on molecular recognitioninbiology, most notablyWatsonCrickbasepairingandenzyme-substrateinteractions.The challenge for nanotechnology is whether

these principles can be used to engineer newconstructs in addition to natural ones.

Molecular nanotechnology: a long-term

view

Molecular nanotechnology, sometimes calledmolecular manufacturing, describes engineered
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nanosystems (nanoscale machines) operatingon the molecular scale. Molecularnanotechnology is especially associated withthemolecular assembler, a machine that canproduce a desired structure or device atom-by-atom using the principles ofmechanosynthesis.

Manufacturing in the context ofproductivenanosystemsis not related to, and should beclearly distinguished from, the conventionaltechnologies used to manufacturenanomaterials such as carbon nanotubes andnanoparticles.

When the term "nanotechnology" wasindependently coined and popularized byEricDrexler(who at the time was unaware of an

earlier usagebyNorio Taniguchi) it referred to afuture manufacturing technology based onmolecular machinesystems. The premise wasthat molecular scale biological analogies oftraditional machine components demonstratedmolecular machines were possible: by thecountless examples found in biology, it is knownthat sophisticated,stochasticallyoptimisedbiological machines can be produced.

It is hoped that developments in

nanotechnology will make possible theirconstruction by some other means, perhapsusingbiomimeticprinciples. However, Drexlerand other researchers[6]have proposed thatadvanced nanotechnology, although perhapsinitially implemented by biomimetic means,ultimately could be based on mechanicalengineering principles, namely, a manufacturingtechnology based on the mechanicalfunctionality of these components (such as

gears, bearings, motors, and structuralmembers) that would enable programmable,positional assembly to atomic specification.[7]The physics and engineering performance ofexemplar designs were analyzed in Drexler'sbook Nanosystems.

In general it is very difficult to assemble deviceson the atomic scale, as all one has to positionatoms are other atoms of comparable size andstickiness. Another view, put forth by CarloMontemagno,[8]is that future nanosystems willbe hybrids of silicon technology and biological

molecular machines. Yet another view, putforward by the lateRichard Smalley, is thatmechanosynthesis is impossible due to thedifficulties in mechanically manipulatingindividual molecules.

This led to an exchange of letters in theACSpublicationChemical & Engineering Newsin2003.[9]Though biology clearly demonstratesthat molecular machine systems are possible,

non-biological molecular machines are todayonly in their infancy. Leaders in research onnon-biological molecular machines are Dr.AlexZettland his colleagues at Lawrence BerkeleyLaboratories and UC Berkeley. They haveconstructed at least three distinct moleculardevices whose motion is controlled from thedesktop with changing voltage: a nanotubenanomotor, a molecular actuator,[10]and ananoelectromechanical relaxation oscillator.[11]

An experiment indicating that positionalmolecular assembly is possible was performedby Ho and Lee atCornell Universityin 1999.They used a scanning tunneling microscope tomove an individual carbon monoxide molecule(CO) to an individual iron atom (Fe) sitting on aflat silver crystal, and chemically bound the COto the Fe by applying a voltage.

Current research

Graphical representation of arotaxane, usefulas a molecular switch.
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Sarfusimage of a DNA biochip elaborated bybottom-up approach.

This device transfers energy from nano-thinlayers ofquantum wellstonanocrystalsabovethem, causing the nanocrystals to emit visiblelight.[12]

Nanomaterials

This includes subfields which develop or studymaterials having unique properties arising fromtheir nanoscale dimensions.[13]

Interface and colloid sciencehas givenrise to many materials which may beuseful in nanotechnology, such as

carbon nanotubesand otherfullerenes,and variousnanoparticlesandnanorods.Nanomaterials with fast ion transportare related also tonanoionicsandnanoelectronics.

Nanoscale materialscan also be used forbulk applications; most present

commercial applications ofnanotechnology are of this flavor.

Progress has been made in using thesematerials for medical applications; seeNanomedicine.

Nanoscale materialsare sometimes usedinsolar cellswhich combats the cost oftraditionalSiliconsolar cells

Development of applicationsincorporating semiconductornanoparticlesto be used in the nextgeneration of products, such as displaytechnology, lighting, solar cells andbiological imaging; seequantum dots.

Bottom-up approaches

These seek to arrange smaller components intomore complex assemblies.

DNA nanotechnologyutilizes thespecificity ofWatsonCrick basepairingto construct well-defined structures outofDNAand othernucleic acids.

Approaches from the field of "classical"chemical synthesisalso aim at designingmolecules with well-defined shape (e.g.

bis-peptides[14]). More generally,molecular self-assembly

seeks to use concepts ofsupramolecularchemistry, andmolecular recognitioninparticular, to cause single-moleculecomponents to automatically arrangethemselves into some usefulconformation.

Top-down approaches

These seek to create smaller devices by usinglarger ones to direct their assembly.

Many technologies that descended fromconventionalsolid-state silicon methodsfor fabricatingmicroprocessorsare nowcapable of creating features smaller than
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100 nm, falling under the definition ofnanotechnology.Giantmagnetoresistance-based hard drivesalready on the market fit thisdescription,[15]as doatomic layerdeposition(ALD) techniques.Peter

GrnbergandAlbert Fertreceived theNobel Prize in Physicsfor their discoveryof Giant magnetoresistance andcontributions to the field of spintronicsin 2007.[16]

Solid-state techniques can also be usedto create devices known asnanoelectromechanical systemsorNEMS, which are related to

microelectromechanical systemsorMEMS. Atomic force microscopetips can be

used as a nanoscale "write head" todeposit a chemical upon a surface in adesired pattern in a process calleddippen nanolithography. This fits into thelarger subfield ofnanolithography.

Focused ion beamscan directly removematerial, or even deposit material whensuitable pre-cursor gasses are applied at

the same time. For example, thistechnique is used routinely to createsub-100 nm sections of material foranalysis inTransmission electronmicroscopy.

Functional approaches

These seek to develop components of a desiredfunctionality without regard to how they might

be assembled.

Molecular electronicsseeks to developmolecules with useful electronicproperties. These could then be used assingle-molecule components in ananoelectronic device. For an exampleseerotaxane.

Synthetic chemical methods can also beused to createsynthetic molecularmotors, such as in a so-callednanocar.

Biomimetic approaches

Bionicsorbiomimicryseeks to applybiological methods and systems found innature, to the study and design ofengineering systems and moderntechnology.Biomineralizationis oneexample of the systems studied.

Bionanotechnologythe use ofbiomoleculesfor applications innanotechnology.

Speculative

These subfields seek toanticipatewhatinventions nanotechnology might yield, orattempt to propose an agenda along whichinquiry might progress. These often take a big-picture view of nanotechnology, with moreemphasis on itssocietal implicationsthan thedetails of how such inventions could actually becreated.

Molecular nanotechnologyis a proposedapproach which involves manipulatingsingle molecules in finely controlled,deterministic ways. This is moretheoretical than the other subfields andis beyond current capabilities.

Nanoroboticscenters on self-sufficientmachines of some functionalityoperating at the nanoscale. There are

hopes for applying nanorobots inmedicine, but it may not be easy to dosuch a thing because of severaldrawbacks of such devices.Nevertheless, progress on innovativematerials and methodologies has beendemonstrated with some patentsgranted about new nanomanufacturing
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stemshttp://en.wikipedia.org/wiki/Nanotechnology#cite_note-15http://en.wikipedia.org/wiki/Nobel_Prize_in_Physicshttp://en.wikipedia.org/wiki/Albert_Ferthttp://en.wikipedia.org/wiki/Peter_Gr%C3%BCnberghttp://en.wikipedia.org/wiki/Peter_Gr%C3%BCnberghttp://en.wikipedia.org/wiki/Peter_Gr%C3%BCnberghttp://en.wikipedia.org/wiki/Atomic_layer_depositionhttp://en.wikipedia.org/wiki/Atomic_layer_depositionhttp://en.wikipedia.org/wiki/Atomic_layer_depositionhttp://en.wikipedia.org/wiki/Nanotechnology#cite_note-14http://en.wikipedia.org/wiki/Giant_magnetoresistancehttp://en.wikipedia.org/wiki/Giant_magnetoresistancehttp://en.wikipedia.org/wiki/Giant_magnetoresistance


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devices for future commercialapplications, which also progressivelyhelps in the development towardsnanorobots with the use of embeddednanobioelectronics concepts.[22][23]

Programmable matterbased onartificialatomsseeks to design materials whoseproperties can be easily, reversibly andexternally controlled.

Due to the popularity and mediaexposure of the term nanotechnology,the wordspicotechnologyandfemtotechnologyhave been coined inanalogy to it, although these are onlyused rarely and informally.

Tools and techniques

TypicalAFMsetup. Amicrofabricatedcantileverwith a sharp tip is deflected by features on asample surface, much like in aphonographbuton a much smaller scale. Alaserbeam reflectsoff the backside of the cantilever into a set ofphotodetectors, allowing the deflection to be

measured and assembled into an image of thesurface.

There are several important moderndevelopments. Theatomic force microscope(AFM) and theScanning Tunneling Microscope(STM) are two early versions of scanning probes

that launched nanotechnology. There are othertypes ofscanning probe microscopy, all flowingfrom the ideas of the scanningconfocalmicroscopedeveloped byMarvin Minskyin1961 and thescanning acoustic microscope(SAM) developed byCalvin Quateand

coworkers in the 1970s, that made it possible tosee structures at the nanoscale. The tip of ascanning probe can also be used to manipulatenanostructures (a process called positionalassembly).Feature-oriented scanning-positioningmethodology suggested by RostislavLapshin appears to be a promising way toimplement these nanomanipulations inautomatic mode. However, this is still a slowprocess because of low scanning velocity of the

microscope. Various techniques ofnanolithographysuch asoptical lithography,X-ray lithographydip pen nanolithography,electron beam lithographyornanoimprintlithographywere also developed. Lithography isa top-down fabrication technique where a bulkmaterial is reduced in size to nanoscale pattern.

Another group of nanotechnological techniquesinclude those used for fabrication of nanowires,those used in semiconductor fabrication such as

deep ultraviolet lithography, electron beamlithography,focused ion beammachining,nanoimprint lithography, atomic layerdeposition, and molecular vapor deposition,and further including molecular self-assemblytechniques such as those employing di-blockcopolymers. However, all of these techniquespreceded the nanotech era, and are extensionsin the development of scientific advancementsrather than techniques which were devised with

the sole purpose of creating nanotechnologyand which were results of nanotechnologyresearch.

The top-down approach anticipatesnanodevices that must be built piece by piece instages, much as manufactured items are made.Scanning probe microscopyis an important
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technique both for characterization andsynthesis of nanomaterials.Atomic forcemicroscopesandscanning tunnelingmicroscopescan be used to look at surfaces andto move atoms around. By designing differenttips for these microscopes, they can be used for

carving out structures on surfaces and to helpguide self-assembling structures. By using, forexample,feature-oriented scanning-positioningapproach, atoms can be moved around on asurface with scanning probe microscopytechniques. At present, it is expensive and time-consuming for mass production but verysuitable for laboratory experimentation.

In contrast, bottom-up techniques build or grow

larger structures atom by atom or molecule bymolecule. These techniques includechemicalsynthesis,self-assemblyand positionalassembly. Another variation of the bottom-upapproach ismolecular beam epitaxyor MBE.Researchers atBell Telephone LaboratorieslikeJohn R. Arthur. Alfred Y. Cho, and Art C. Gossarddeveloped and implemented MBE as a researchtool in the late 1960s and 1970s. Samples madeby MBE were key to the discovery of thefractional quantum Hall effect for which the

1998Nobel Prize in Physicswas awarded. MBEallows scientists to lay down atomically-preciselayers of atoms and, in the process, build upcomplex structures. Important for research onsemiconductors, MBE is also widely used tomake samples and devices for the newlyemerging field ofspintronics.

However, new therapeutic products, based onresponsive nanomaterials, such as the

ultradeformable, stress-sensitiveTransfersomevesicles, are under development and alreadyapproved for human use in some countries.

Applications

As of August 21, 2008, theProject on EmergingNanotechnologiesestimates that over 800manufacturer-identified nanotech products arepublicly available, with new ones hitting themarket at a pace of 34 per week.[24]Theproject lists all of the products in a publicly

accessible onlineinventory. Most applicationsare limited to the use of "first generation"passive nanomaterials which includes titaniumdioxide in sunscreen, cosmetics and some foodproducts; Carbon allotropes used to producegecko tape; silver in food packaging, clothing,disinfectants and household appliances; zincoxide in sunscreens and cosmetics, surfacecoatings, paints and outdoor furniturevarnishes; and cerium oxide as a fuel catalyst.[25]

TheNational Science Foundation(a majordistributor for nanotechnology research in theUnited States) funded researcher David Berubeto study the field of nanotechnology. Hisfindings are published in the monographNano-Hype: The Truth Behind the NanotechnologyBuzz. This study concludes that much of what issold as nanotechnology is in fact a recasting

of straightforward materials science, which isleading to a nanotech industry built solely on

selling nanotubes, nanowires, and the likewhich will end up with a few suppliers selling

low margin products in huge volumes." Furtherapplications which require actual manipulationor arrangement of nanoscale components awaitfurther research. Though technologies brandedwith the term 'nano' are sometimes littlerelated to and fall far short of the mostambitious and transformative technologicalgoals of the sort in molecular manufacturing

proposals, the term still connotes such ideas.According to Berube, there may be a dangerthat a "nano bubble" will form, or is formingalready, from the use of the term by scientistsand entrepreneurs to garner funding, regardlessof interest in the transformative possibilities ofmore ambitious and far-sighted work.[26]
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Nano-membranes have been produced that areportable and easily-cleaned systems that purify,detoxify and desalinate water meaning thatthird-world countries could get clean water,solving many water related health issues.[27]

Implications

Because of the far-ranging claims that havebeen made about potential applications ofnanotechnology, a number of serious concernshave been raised about what effects these willhave on our society if realized, and what actionif any is appropriate to mitigate these risks.

There are possible dangers that arise with the

development of nanotechnology. TheCenter forResponsible Nanotechnologysuggests that newdevelopments could result, among other things,in untraceable weapons of mass destruction,networked cameras for use by the government,and weapons developments fast enough todestabilize arms races ("NanotechnologyBasics").

One area of concern is the effect that industrial-scale manufacturing and use ofnanomaterialswould have on human health and theenvironment, as suggested bynanotoxicologyresearch. Groups such as the Center forResponsible Nanotechnology have advocatedthat nanotechnology should bespeciallyregulatedby governments for these reasons.Others counter that overregulation would stiflescientific research and the development ofinnovations whichcould greatly benefitmankind.

Other experts, including director of theWoodrow Wilson Center'sProject on EmergingNanotechnologiesDavid Rejeski, havetestified[28]that successful commercializationdepends on adequate oversight, risk researchstrategy, and public engagement.Berkeley,

Californiais currently the only city in the UnitedStates to regulate nanotechnology;[29]Cambridge, Massachusettsin 2008 consideredenacting a similar law,[30]but ultimately rejectedthis.[31]

Health and environmental concerns

Some of the recently developed nanoparticleproducts may haveunintended consequences.Researchers have discovered that silvernanoparticles used in socks only to reduce footodor are being released in the wash withpossible negative consequences.[32]Silvernanoparticles, which arebacteriostatic, maythen destroy beneficial bacteria which are

important for breaking down organic matter inwaste treatment plants or farms.[33]

A study at theUniversity of Rochesterfoundthat when rats breathed in nanoparticles, theparticles settled in the brain and lungs, whichled to significant increases in biomarkers forinflammation and stress response.[34]A study inChina indicated that nanoparticles induce skinaging through oxidative stress in hairlessmice.[35][36]

A major study published more recently inNature Nanotechnologysuggests some forms ofcarbon nanotubes a poster child for thenanotechnology revolution could be asharmful asasbestosif inhaled in sufficientquantities. Anthony Seaton of the Institute ofOccupational Medicine in Edinburgh, Scotland,who contributed to the article oncarbonnanotubessaid "We know that some of them

probably have the potential to causemesothelioma. So those sorts of materials needto be handled very carefully.".[37]In the absenceof specific nano-regulation forthcoming fromgovernments, Paull and Lyons (2008) havecalled for an exclusion of engineerednanoparticles from organic food.[38]Anewspaper article reports that workers in a
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paint factory developed serious lung diseaseand nanoparticles were found in their lungs.[39]

Regulation

Calls for tighter regulation of nanotechnology

have occurred alongside a growing debaterelated to the human health and safety risksassociated with nanotechnology. Furthermore,there is significant debate about who isresponsible for the regulation ofnanotechnology. While some non-nanotechnology specific regulatory agenciescurrently cover some products and processes(to varying degrees)by bolting onnanotechnology to existing regulations there

are clear gaps in these regimes.

[40]

In"Nanotechnology Oversight: An Agenda for theNext Administration,"[41]former EPA deputyadministrator J. Clarence (Terry) Davies lays outa clear regulatory roadmap for the nextpresidential administration and describes theimmediate and longer term steps necessary todeal with the current shortcomings ofnanotechnology oversight.

Stakeholders concerned by the lack of a

regulatory framework to assess and controlrisks associated with the release ofnanoparticles and nanotubes have drawnparallels withbovine spongiformencephalopathy(mad cows disease),thalidomide, genetically modified food,[42]nuclear energy, reproductive technologies,biotechnology, andasbestosis. Dr. AndrewMaynard, chief science advisor to the WoodrowWilson CentersProject on Emerging

Nanotechnologies, concludes (among others)that there is insufficient funding for humanhealth and safety research, and as a result thereis currently limited understanding of the humanhealth and safety risks associated withnanotechnology.[43]As a result, some academicshave called for stricter application of theprecautionary principle, with delayed marketing

approval, enhanced labelling and additionalsafety data development requirements inrelation to certain forms of nanotechnology.[44]

TheRoyal Societyreport[45]identified a risk ofnanoparticles or nanotubes being released

during disposal, destruction and recycling, andrecommended that manufacturers of products

that fall under extended producer responsibilityregimes such as end-of-life regulations publishprocedures outlining how these materials willbe managed to minimize possible human andenvironmental exposure (p.xiii). Reflecting the

challenges for ensuring responsible life cycleregulation, theInstitute for Food andAgricultural Standardshas proposed standards

for nanotechnology research and developmentshould be integrated across consumer, workerand environmental standards. They alsopropose thatNGOsand other citizen groupsplay a meaningful role in the development ofthese standards.

In October 2008, the Department of ToxicSubstances Control (DTSC), within the CaliforniaEnvironmental Protection Agency, announcedits intent to request information regarding

analytical test methods, fate and transport inthe environment, and other relevantinformation from manufacturers of carbonnanotubes.[46]The purpose of this informationrequest will be to identify information gaps andto develop information about carbonnanotubes, an important emergingnanomaterial.
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Quantum dot

Colloidal quantum dots irradiated with a UVlight. Different sized quantum dots emitdifferent color light due to quantumconfinement.

A quantum dot is asemiconductorwhoseexcitonsareconfinedin all threespatialdimensions. As a result, they have propertiesthat are between those of bulk semiconductorsand those of discretemolecules.[1][2][3]Theywere discovered byLouis E. Brus, who was thenatBell Labs. The term "Quantum Dot" was

coined byMark Reed.

Researchers have studied quantum dots intransistors,solar cells,LEDs, anddiode lasers.They have also investigated quantum dots asagentsformedical imagingand hope to usethem asqubits.

In layman's terms, quantum dots aresemiconductors whose conductingcharacteristics are closely related to the sizeand shape of the individual crystal. Generally,the smaller the size of the crystal, the larger theband gap, the greater the difference in energybetween the highestvalence bandand thelowestconduction bandbecomes, thereforemore energy is needed to excite the dot, andconcurrently, more energy is released when the

crystal returns to its resting state. For example,in fluorescent dye applications, this equates tohigher frequencies of light emitted afterexcitation of the dot as the crystal size growssmaller, resulting in a color shift from red toblue in the light emitted. The main advantages

in using quantum dots is that because of thehigh level of control possible over the size of thecrystals produced, it is possible to have veryprecise control over the conductive propertiesof the material.[4]

Quantum confinement in

semiconductors

3D confined electron wave functions in aQuantum Dot. Here, rectangular and triangular-shaped quantum dots are shown. Energy statesin rectangular dots are more s-type and p-type. However, in a triangular dot the wave

functions are mixed due to confinementsymmetry.

In an unconfined (bulk) semiconductor, anelectron-hole pair is typically bound within acharacteristic length, which is called theexcitonBohr radiusand is estimated by replacing thepositively charged atomic core with the hole inthe Bohr formula. If the electron and hole areconstrained further, then properties of thesemiconductor change. This effect is a form of

quantum confinement, and it is a key feature inmany emerging electronic structures.[5][6]

Besides confinement in all three dimensions i.e.Quantum Dot - other quantum confinedsemiconductors include:
http://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Potential_wellhttp://en.wikipedia.org/wiki/Potential_wellhttp://en.wikipedia.org/wiki/Potential_wellhttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Quantum_dot#cite_note-2http://en.wikipedia.org/wiki/Quantum_dot#cite_note-2http://en.wikipedia.org/wiki/Louis_E._Brushttp://en.wikipedia.org/wiki/Louis_E._Brushttp://en.wikipedia.org/wiki/Louis_E._Brushttp://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/Mark_Reed_(physicist)http://en.wikipedia.org/wiki/Mark_Reed_(physicist)http://en.wikipedia.org/wiki/Mark_Reed_(physicist)http://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Laser_diodehttp://en.wikipedia.org/wiki/Laser_diodehttp://en.wikipedia.org/wiki/Laser_diodehttp://en.wikipedia.org/wiki/Stainhttp://en.wikipedia.org/wiki/Stainhttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Quantum_computinghttp://en.wikipedia.org/wiki/Quantum_computinghttp://en.wikipedia.org/wiki/Quantum_computinghttp://en.wikipedia.org/wiki/Band_gaphttp://en.wikipedia.org/wiki/Band_gaphttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-3http://en.wikipedia.org/wiki/Quantum_dot#cite_note-3http://en.wikipedia.org/wiki/Quantum_dot#cite_note-3http://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Bohr_radiushttp://en.wikipedia.org/wiki/Bohr_radiushttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/File:QD_mini_rainbow.jpghttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/Quantum_dot#cite_note-4http://en.wikipedia.org/wiki/Bohr_radiushttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-3http://en.wikipedia.org/wiki/Conduction_bandhttp://en.wikipedia.org/wiki/Valence_bandhttp://en.wikipedia.org/wiki/Band_gaphttp://en.wikipedia.org/wiki/Quantum_computinghttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Stainhttp://en.wikipedia.org/wiki/Laser_diodehttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/Solar_cellhttp://en.wikipedia.org/wiki/Transistorhttp://en.wikipedia.org/wiki/Mark_Reed_(physicist)http://en.wikipedia.org/wiki/Bell_Labshttp://en.wikipedia.org/wiki/Louis_E._Brushttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-2http://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Quantum_dot#cite_note-0http://en.wikipedia.org/wiki/Moleculeshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Spatial_dimensionshttp://en.wikipedia.org/wiki/Potential_wellhttp://en.wikipedia.org/wiki/Excitonhttp://en.wikipedia.org/wiki/Semiconductor


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1. quantum wires, which confine electronsor holes in two spatial dimensions andallow free propagation in the third.

2. quantum wells, which confine electronsor holes in one dimension and allow freepropagation in two dimensions.

Making quantum dots

There are several ways to confine excitons insemiconductors, resulting in different methodsto produce quantum dots. In general, quantumwires, wells and dots are grown by advancedepitaxialtechniques innanocrystalsproducedby chemical methods or by ion implantation, orinnanodevicesmade by state-of-the-art

lithographictechniques.[7]

Colloidal synthesis

Colloidalsemiconductornanocrystalsaresynthesizedfrom precursor compoundsdissolved in solutions, much like traditionalchemical processes. The synthesis ofcolloidalquantum dots is based on a three-componentsystem composed of: precursors, organic

surfactants, and solvents. When heating areaction medium to a sufficiently hightemperature, the precursors chemicallytransform intomonomers. Once the monomersreach a high enoughsupersaturationlevel, thenanocrystal growth starts with a nucleationprocess. The temperature during the growthprocess is one of the critical factors indetermining optimal conditions for thenanocrystal growth. It must be high enough toallow for rearrangement andannealingof

atoms during the synthesis process while beinglow enough to promote crystal growth. Anothercritical factor that has to be stringentlycontrolled during nanocrystal growth is themonomer concentration. The growth process ofnanocrystals can occur in two different regimes,focusing and defocusing. At high monomer

concentrations, the critical size (the size wherenanocrystals neither grow nor shrink) isrelatively small, resulting in growth of nearly allparticles. In this regime, smaller particles growfaster than large ones (since larger crystals needmore atoms to grow than small crystals)

resulting in focusing of the size distribution toyield nearly monodisperse particles. The sizefocusing is optimal when the monomerconcentration is kept such that the averagenanocrystal size present is always slightly largerthan the critical size. When the monomerconcentration is depleted during growth, thecritical size becomes larger than the averagesize present, and the distribution defocuses as

a result ofOstwald ripening.

There are colloidal methods to produce manydifferent semiconductors, includingcadmiumselenide,cadmium sulfide,indium arsenide, andindium phosphide. These quantum dots cancontain as few as 100 to 100,000 atoms withinthe quantum dot volume, with a diameter of 10to 50 atoms. This corresponds to about 2 to 10nanometers, and at 10 nm in diameter, nearly 3million quantum dots could be lined up end toend and fit within the width of a human thumb.

Large batches of quantum dots may besynthesized viacolloidal synthesis. Due to thisscalability and the convenience ofbenchtopconditions, colloidal synthetic methods arepromising for commercial applications. It isacknowledged[citation needed] to be the least toxicof all the different forms of synthesis.

Fabrication

Self-assembled quantum dots aretypically between 5 and 50 nm in size.Quantum dots defined bylithographicallypatternedgateelectrodes, or by etching on two-dimensional electron gases insemiconductor heterostructures can
http://en.wikipedia.org/wiki/Quantum_wirehttp://en.wikipedia.org/wiki/Quantum_wirehttp://en.wikipedia.org/wiki/Quantum_wellhttp://en.wikipedia.org/wiki/Quantum_wellhttp://en.wikipedia.org/wiki/Epitaxialhttp://en.wikipedia.org/wiki/Epitaxialhttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Nanobothttp://en.wikipedia.org/wiki/Nanobothttp://en.wikipedia.org/wiki/Nanobothttp://en.wikipedia.org/wiki/Lithographyhttp://en.wikipedia.org/wiki/Lithographyhttp://en.wikipedia.org/wiki/Quantum_dot#cite_note-6http://en.wikipedia.org/wiki/Quantum_dot#cite_note-6http://en.wikipedia.org/wiki/Quantum_dot#cite_note-6http://en.wikipedia.org/wiki/Colloidhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Nanocrystalhttp://en.wikipedia.org/wiki/Nanocrystalhttp://www.youtube.com/results?search_query=quantum+dot&search_type=http://www.youtube.com/results?search_query=quantum+dot&search_type=http://en.wikipedia.org/wiki/Chemical_synthesishttp://en.wikipedia.org/wiki/Chemical_synthesishttp://en.wikipedia.org/wiki/Colloidalhttp://en.wikipedia.org/wiki/Colloidalhttp://en.wikipedia.org/wiki/Colloidalhttp://en.wikipedia.org/wiki/Monomershttp://en.wikipedia.org/wiki/Monomershttp://en.wikipedia.org/wiki/Monomershttp://en.wikipedia.org/wiki/Supersaturationhttp://en.wikipedia.org/wiki/Supersaturationhttp://en.wikipedia.org/wiki/Supersaturationhttp://en.wikipedia.org/wiki/Annealinghttp://en.wikipedia.org/wiki/Annealinghttp://en.wikipedia.org/wiki/Annealinghttp://en.wikipedia.org/wiki/Ostwald_ripeninghttp://en.wikipedia.org/wiki/Ostwald_ripeninghttp://en.wikipedia.org/wiki/Ostwald_ripeninghttp://en.wikipedia.org/wiki/Cadmium_selenidehttp://en.wikipedia.org/wiki/Cadmium_selenidehttp://en.wikipedia.org/wiki/Cadmium_selenidehttp://en.wikipedia.org/wiki/Cadmium_selenidehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Cadmium_sulfidehttp://en.wikipedia.org/wiki/Indium_arsenidehttp://en.wikipedia.org/wiki/Indium_arsenidehttp://en.wikipedia.org/wiki/Indium_arsenidehttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/Indium_phosphidehttp://en.wikipedia.org/wiki/Nanometerhttp://en.wikipedia.org/wiki/Nanometerhttp://en.wikipedia.org/wiki/Colloidal_synthesishttp://en.wikipedia.org/wiki/Colloidal_synthesishttp://en.wikipedia.org/wiki/Colloidal_synthesishttp://en.wikipedia.org/wiki/Benchtop_conditionshttp://en.wikipedia.org/wiki/Benchtop_conditionshttp://en.wikipedia.org/wiki/Benchtop_conditionshttp://en.wikiped

Documents

Nanotech, Drug Delivery, CNT