nanoscience and nanotechnologies: opportunities and uncertainties
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The Royal Society 2004
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1 Introduction 11.1 Hopes and concerns about nanoscience and nanotechnologies 11.2 Terms of reference and conduct of the study 21.3 Report overview 21.4 Next steps 3
2 What are nanoscience and nanotechnologies? 5
3 Science and applications 73.1 Introduction 73.2 Nanomaterials 7
3.2.1 Introduction to nanomaterials 73.2.2 Nanoscience in this area 83.2.3 Applications 10
3.3 Nanometrology 133.3.1 Introduction to nanometrology 133.3.2 Length measurement 133.3.3 Force measurement 143.3.4 Measurement of single molecules 143.3.5 Applications 14
3.4 Electronics, optoelectronics, and information and communication technology (ICT) 173.4.1 Introduction to electronics, optoelectronics, and ICT 173.4.2 Nanoscience in this area 173.4.3 Current applications 173.4.4 Applications anticipated in the future 18
3.5 Bio-nanotechnology and nanomedicine 193.5.1 Introduction to bio-nanotechnology and nanomedicine 193.5.2 Nanoscience in this area 203.5.3 Current and future applications 20
4 Nanomanufacturing and the industrial application of nanotechnologies 254.1 Introduction 254.2 Characterisation 254.3 Fabrication techniques 25
4.3.1 Bottom-up manufacturing 264.3.2 Top-down manufacturing 284.3.3 Convergence of top-down and bottom-up techniques 29
4.4 Visions for the future 304.4.1 Precision Engineering 304.4.2 The chemicals industry 314.4.3 The information and communication technology industry 31
4.5 Resource management and environmental issues 324.6 Barriers to progress 324.7 Summary 33
Nanoscience and nanotechnologies: opportunities and uncertainties
5 Possible adverse health, environmental and safety impacts 355.1 Introduction 355.2 Assessing and controlling risk 355.3 Human health 36
5.3.1 Understanding the toxicity of nanoparticles and fibres 365.3.2 Manufactured nanoparticles and nanotubes 41
5.4 Effects on the environment and other species 455.5 Risk of explosion 475.6 Addressing the knowledge gaps 475.7 Conclusions 49
6 Social and ethical issues 516.1 Introduction: framing social and ethical issues 516.2 Economic impacts 526.3 A nanodivide? 526.4 Information collection and the implications for civil liberties 536.5 Human enhancement 546.6 Covergence 546.7 Military uses 556.8 Conclusions 56
7 Stakeholder and public dialogue 597.1 Introduction 597.2 Current public awareness of nanotechnologies in Britain 59
7.2.1 Quantitative survey findings 597.2.2 Qualitative workshop findings 607.2.3 Interpreting the research into public attitudes 61
7.3 Importance of promoting a wider dialogue 627.4 Nanotechnologies as an upstream issue 647.5 Designing dialogue on nanotechnologies 64
7.5.1 Incorporating public values in decisions 667.5.2 Improving decision quality 667.5.3 Resolving conflict 667.5.4 Improving trust in institutions 667.5.5 Informing or educating people 66
7.6 Conclusions 67
8 Regulatory issues 698.1 Introduction 698.2 Approaches to regulation 698.3 Case studies 70
8.3.1 Workplace (including research laboratories) 708.3.2 Marketing and use of chemicals 718.3.3 Consumer products incorporating free nanoparticles, particularly skin preparations 728.3.4 Medicines and medical devices 748.3.5 Consumer products incorporating fixed nanoparticles: end-of-life issues 74
8.4 Knowledge gaps 748.4.1 Hazard 748.4.2 Exposure 758.4.3 Measurement 75
8.5 Conclusions 76
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9 Conclusions 799.1 Nanoscience and nanotechnologies and their industrial application 799.2 Health, safety and environmental risks and hazards 799.3 Social and ethical impacts 819.4 Stakeholder and public dialogue 819.5 Regulation 829.6 Responsible development of nanotechnologies 839.7 A mechanism for addressing future issues 84
10 Recommendations 85
11 References 89
A Working Group, Review Group and Secretariat 95
B Conduct of the study 97
C List of those who submitted evidence 99
D Mechanical self-replicating nano-robots and Grey Goo 109
Acronyms and abbreviations 111
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1 Nanoscience and nanotechnologies are widely seenas having huge potential to bring benefits to many areasof research and application, and are attracting rapidlyincreasing investments from Governments and frombusinesses in many parts of the world. At the same time,it is recognised that their application may raise newchallenges in the safety, regulatory or ethical domainsthat will require societal debate. In June 2003 the UKGovernment therefore commissioned the Royal Societyand the Royal Academy of Engineering to carry out thisindependent study into current and future developmentsin nanoscience and nanotechnologies and their impacts.
2 The remit of the study was to:
define what is meant by nanoscience andnanotechnologies;
summarise the current state of scientific knowledgeabout nanotechnologies;
identify the specific applications of the newtechnologies, in particular where nanotechnologies arealready in use;
carry out a forward look to see how the technologiesmight be used in future, where possible estimating thelikely timescales in which the most far-reachingapplications of the technologies might become reality;
identify what health and safety, environmental, ethicaland societal implications or uncertainties may arisefrom the use of the technologies, both current andfuture; and
identify areas where additional regulation needs to beconsidered.
3 In order to carry out the study, the two Academiesset up a Working Group of experts from the relevantdisciplines in science, engineering, social science andethics and from two major public interest groups. Thegroup consulted widely, through a call for writtenevidence and a series of oral evidence sessions andworkshops with a range of stakeholders from both theUK and overseas. It also reviewed published literatureand commissioned new research into public attitudes.Throughout the study, the Working Group hasconducted its work as openly as possible and haspublished the evidence received on a dedicated websiteas it became available (www.nanotec.org.uk).
4 This report has been reviewed and endorsed by theRoyal Society and the Royal Academy of Engineering.
Significance of the nanoscale
5 A nanometre (nm) is one thousand millionth of ametre. For comparison, a single human hair is about80,000 nm wide, a red blood cell is approximately 7,000nm wide and a water molecule is almost 0.3nm across.People are interested in the nanoscale (which we defineto be from 100nm down to the size of atoms(approximately 0.2nm)) because it is at this scale thatthe properties of materials can be very different fromthose at a larger scale. We define nanoscience as thestudy of phenomena and manipulation of materials atatomic, molecular and macromolecular scales, whereproperties differ significantly from those at a largerscale; and nanotechnologies as the design,characterisation, production and application ofstructures, devices and systems by controlling shape andsize at the nanometre scale. In some senses,nanoscience and nanotechnologies are not new.Chemists have been making polymers, which are largemolecules made up of nanoscale subunits, for manydecades and nanotechnologies have been used tocreate the tiny features on computer chips for the past20 years. However, advances in the tools that now allowatoms and molecules to be examined and probed withgreat precision have enabled the expansion anddevelopment of nanoscience and nanotechnologies.
6 The properties of materials can be different at thenanoscale for two main reasons. First, nanomaterials havea relatively larger surface area when compared to thesame mass of material produced in a larger form. This canmake materials more chemically reactive (in some casesmaterials that are inert in their larger form are reactivewhen produced in their nanoscale form), and affect theirstrength or electrical properties. Second, quantum effectscan begin to dominate the behaviour of matter at thenanoscale - particularly at the lower end - affecting theoptical, electrical and magnetic behaviour of materials.Materials can be produced that are nanoscale in onedimension (for example, very thin surface coatings), intwo dimensions (for example, nanowires and nanotubes)or in all three dimensions (for example, nanoparticles).
7 Our wide-ranging definitions cut across manytraditional scientific disciplines. The only featurecommon to the diverse activities characterised asnanotechnology is the tiny dimensions on which theyoperate. We have therefore found it more appropriateto refer to nanotechnologies.
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Current and potential uses of nanoscienceand nanotechnologies
8 Our aim has been to provide an overview of currentand potential future developments in nanoscience andnanotechnologies against which the health, safety,environmental, social and ethical implications can beconsidered. We did not set out to identify areas ofnanoscience and nanotechnologies that should beprioritised for funding.
9 Much of nanoscience and many nanotechnologiesare concerned with producing new or enhanced materi-als. Nanomaterials can be constructed by 'top down'techniques, producing very small structures from largerpieces of material, for example by etching to create cir-cuits on the surface of a silicon microchip. They mayalso be constructed by 'bottom up' techniques, atomby atom or molecule by molecule. One way of doingthis is self-assembly, in which the atoms or moleculesarrange themselves into a structure due to their naturalproperties. Crystals grown for the semiconductor indus-try provide an example of self assembly, as does chemi-cal synthesis of large molecules. A second way is to usetools to move each atom or molecule individually.Although this positional assembly offers greater con-trol over construction, it is currently very laborious andnot suitable for industrial applications.
10 Current applications of nanoscale materials includevery thin coatings used, for example, in electronics andactive surfaces (for example, self-cleaning windows). Inmost applications the nanoscale components will befixed or embedded but in some, such as those used incosmetics and in some pilot environmental remediationapplications, free nanoparticles are used. The ability tomachine materials to very high precision and accuracy(better than 100nm) is leading to considerable benefitsin a wide range of industrial sectors, for example in theproduction of components for the information andcommunication technology (ICT), automotive and aero-space industries.
11 It is rarely possible to predict accurately thetimescale of developments, but we expect that in thenext few years nanomaterials will provide ways ofimproving performance in a range of products includingsilicon-based electronics, displays, paints, batteries,micro-machined silicon sensors and catalysts. Furtherinto the future we may see composites that exploit theproperties of carbon nanotubes rolls of carbon withone or more walls, measuring a few nanometres indiameter and up to a few centimetres in length whichare extremely strong and flexible and can conductelectricity. At the moment the applications of thesetubes are limited by the difficulty of producing them in auniform manner and separating them into individualnanotubes. We may also see lubricants based on
inorganic nanospheres; magnetic materials usingnanocrystalline grains; nanoceramics used for moredurable and better medical prosthetics; automotivecomponents or high-temperature furnaces; and nano-engineered membranes for more energy-efficient waterpurification.
12 Metrology, the science of measurement, underpinsall other nanoscience and nanotechnologies because itallows the characterisation of materials in terms ofdimensions but also in terms of attributes such as elec-trical properties and mass. Greater precision in metrolo-gy will assist the development of nanoscience and nan-otechnologies. However, this will require increased stan-dardisation to allow calibration of equipment and werecommend that the Department of Trade and Industryensure that this area is properly funded.
(iii) Electronics, optoelectronics and ICT
13 The role of nanoscience and nanotechnologies inthe development of information technology is anticipat-ed in the International Technology Roadmap forSemiconductors, a worldwide consensus document thatpredicts the main trends in the semiconductor industryup to 2018. This roadmap defines a manufacturingstandard for silicon chips in terms of the length of aparticular feature in a memory cell. For 2004 the stan-dard is 90 nm, but it is predicted that by 2016 this willbe just 22 nm. Much of the miniaturisation of computerchips to date has involved nanoscience and nanotech-nologies, and this is expected to continue in the shortand medium term. The storage of data, using optical ormagnetic properties to create memory, will also dependon advances in nanoscience and nanotechnologies.
14 Alternatives to silicon-based electronics are alreadybeing explored through nanoscience andnanotechnologies, for example plastic electronics forflexible display screens. Other nanoscale electronicdevices currently being developed are sensors to detectchemicals in the environment, to check the edibility offoodstuffs, or to monitor the state of mechanicalstresses within buildings. Much interest is also focusedon quantum dots, semiconductor nanoparticles that canbe tuned to emit or absorb particular light colours foruse in solar energy cells or fluorescent biological labels.
(iv) Bionanotechnology and nanomedicine
15 Applications of nanotechnologies in medicine areespecially promising, and areas such as disease diagno-sis, drug delivery targeted at specific sites in the bodyand molecular imaging are being intensively investigat-ed and some products are undergoing clinical trials.Nanocrystalline silver, which is known to have antimi-crobial properties, is being used in wound dressings inthe USA. Applications of nanoscience and nanotech-
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nologies are also leading to the production of materialsand devices such as scaffolds for cell and tissue engi-neering, and sensors that can be used for monitoringaspects of human health. Many of the applications maynot be realised for ten years or more (owing partly tothe rigorous testing and validation regimes that will berequired). In the much longer term, the development ofnanoelectronic systems that can detect and processinformation could lead to the development of an artifi-cial retina or cochlea. Progress in the area of bionan-otechnology will build on our understanding of naturalbiological structures on the molecular scale, such asproteins.
(v) Industrial applications
16 So far, the relatively small number of applications ofnanotechnologies that have made it through toindustrial application represent evolutionary rather thanrevolutionary advances. Current applications are mainlyin the areas of determining the properties of materials,the production of chemicals, precision manufacturingand computing. In mobile phones for instance, materialsinvolving nanotechnologies are being developed for usein advanced batteries, electronic packaging and indisplays. The total weight of these materials willconstitute a very small fraction of the whole product butbe responsible for most of the functions that the devicesoffer. In the longer term, many more areas may beinfluenced by nanotechnologies but there will besignificant challenges in scaling up production from theresearch laboratory to mass manufacturing.
17 In the longer term it is hoped thatnanotechnologies will enable more efficient approachesto manufacturing which will produce a host of multi-functional materials in a cost-effective manner, withreduced resource use and waste. However, it isimportant that claims of likely environmental benefitsare assessed for the entire lifecycle of a material orproduct, from its manufacture through its use to itseventual disposal. We recommend that lifecycleassessments be undertaken for applications ofnanotechnologies.
18 Hopes have been expressed for the developmentand use of mechanical nano-machines which would becapable of producing materials (and themselves) atom-by-atom (however this issue was not raised by theindustrial representatives to whom we spoke). Alongsidesuch hopes for self-replicating machines, fears havebeen raised about the potential for these (as yetunrealised) machines to go out of control, produceunlimited copies of themselves, and consume allavailable material on the planet in the process (the socalled grey goo scenario). We have concluded thatthere is no evidence to suggest that mechanical self-replicating nanomachines will be developed in theforeseeable future.
Health and environmental impacts
19 Concerns have been expressed that the veryproperties of nanoscale particles being exploited incertain applications (such as high surface reactivity andthe ability to cross cell membranes) might also havenegative health and environmental impacts. Manynanotechnologies pose no new risks to health andalmost all the concerns relate to the potential impacts ofdeliberately manufactured nanoparticles and nanotubesthat are free rather than fixed to or within a material.Only a few chemicals are being manufactured innanoparticulate form on an industrial scale andexposure to free manufactured nanoparticles andnanotubes is currently limited to some workplaces(including academic research laboratories) and a smallnumber of cosmetic uses. We expect the likelihood ofnanoparticles or nanotubes being released fromproducts in which they have been fixed or embedded(such as composites) to be low but have recommendedthat manufacturers assess this potential exposure riskfor the lifecycle of the product and make their findingsavailable to the relevant regulatory bodies.
20 Few studies have been published on the effects ofinhaling free manufactured nanoparticles and we havehad to rely mainly on analogies with results from studieson exposure to other small particles such as thepollutant nanoparticles known to be present in largenumbers in urban air, and the mineral dusts in someworkplaces. The evidence suggests that at least somemanufactured nanoparticles will be more toxic per unitof mass than larger particles of the same chemical. Thistoxicity is related to the surface area of nanoparticles(which is greater for a given mass than that of largerparticles) and the chemical reactivity of the surface(which could be increased or decreased by the use ofsurface coatings). It also seems likely that nanoparticleswill penetrate cells more readily than larger particles.
21 It is very unlikely that new manufacturednanoparticles could be introduced into humans in dosessufficient to cause the health effects that have beenassociated with the nanoparticles in polluted air.However, some may be inhaled in certain workplaces insignificant amounts and steps should be taken tominimise exposure. Toxicological studies haveinvestigated nanoparticles of low solubility and lowsurface activity. Newer nanoparticles with characteristicsthat differ substantially from these should be treatedwith particular caution. The physical characteristics ofcarbon and other nanotubes mean that they may havetoxic properties similar to those of asbestos fibres,although preliminary studies suggest that they may notreadily escape into the air as individual fibres. Untilfurther toxicological studies have been undertaken,human exposure to airborne nanotubes in laboratoriesand workplaces should be restricted.
22 If nanoparticles penetrate the skin they might facil-itate the production of reactive molecules that couldlead to cell damage. There is some evidence to showthat nanoparticles of titanium dioxide (used in somesun protection products) do not penetrate the skin butit is not clear whether the same conclusion holds forindividuals whose skin has been damaged by sun or bycommon diseases such as eczema. There is insufficientinformation about whether other nanoparticles used incosmetics (such as zinc oxide) penetrate the skin andthere is a need for more research into this. Much of theinformation relating to the safety of these ingredientshas been carried out by industry and is not published inthe open scientific literature. We therefore recommendthat the terms of reference of safety advisory commit-tees that consider information on the toxicology ofingredients such as nanoparticles include a requirementfor relevant data, and the methodologies used toobtain them, to be placed in the public domain.
23 Important information about the fate and behav-iour of nanoparticles that penetrate the bodys defencescan be gained from researchers developing nanoparti-cles for targeted drug delivery. We recommend collabo-ration between these researchers and those investigat-ing the toxicity of other nanoparticles and nanotubes.In addition, the safety testing of these novel drug deliv-ery methods must consider the toxic properties specificto such particles, including their ability to affect cellsand organs distant from the intended target of thedrug.
24 There is virtually no information available about theeffect of nanoparticles on species other than humans orabout how they behave in the air, water or soil, orabout their ability to accumulate in food chains. Untilmore is known about their environmental impact weare keen that the release of nanoparticles and nan-otubes to the environment is avoided as far as possible.Specifically, we recommend as a precautionary measurethat factories and research laboratories treat manufac-tured nanoparticles and nanotubes as if they were haz-ardous and reduce them from waste streams and thatthe use of free nanoparticles in environmental applica-tions such as remediation of groundwater be prohibit-ed.
25 There is some evidence to suggest that com-bustible nanoparticles might cause an increased risk ofexplosion because of their increased surface area andpotential for enhanced reaction. Until this hazard hasbeen properly evaluated this risk should be managed bytaking steps to avoid large quantities of these nanopar-ticles becoming airborne.
26 Research into the hazards and exposure pathwaysof nanoparticles and nanotubes is required to reducethe many uncertainties related to their potentialimpacts on health, safety and the environment. Thisresearch must keep pace with the future development
of nanomaterials. We recommend that the UK ResearchCouncils assemble an interdisciplinary centre (perhapsfrom existing research institutions) to undertakeresearch into the toxicity, epidemiology, persistence andbioaccumulation of manufactured nanoparticles andnanotubes, to work on exposure pathways and todevelop measurement methods. The centre should liaiseclosely with regulators and with other researchers in theUK, Europe and internationally. We estimate that fund-ing of 5-6M pa for 10 years will be required. Corefunding should come from the Government but thecentre would also take part in European and interna-tionally funded projects.
Social and ethical impacts
27 If it is difficult to predict the future direction ofnanoscience and nanotechnologies and the timescaleover which particular developments will occur, it is evenharder to predict what will trigger social and ethicalconcerns. In the short to medium term concerns areexpected to focus on two basic questions: Whocontrols uses of nanotechnologies? and Who benefitsfrom uses of nanotechnologies?. These questions arenot unique to nanotechnologies but past experiencewith other technologies demonstrates that they willneed to be addressed.
28 The perceived opportunities and threats ofnanotechnologies often stem from the samecharacteristics. For example, the convergence ofnanotechnologies with information technology, linkingcomplex networks of remote sensing devices withsignificant computational power, could be used toachieve greater personal safety, security andindividualised healthcare and to allow businesses totrack and monitor their products. It could equally beused for covert surveillance, or for the collection anddistribution of information without adequate consent.As new forms of surveillance and sensing are developed,further research and expert legal analysis might benecessary to establish whether current regulatoryframeworks and institutions provide appropriatesafeguards to individuals and groups in society. In themilitary context, too, nanotechnologies hold potentialfor both defence and offence and will therefore raise anumber of social and ethical issues.
29 There is speculation that a possible futureconvergence of nanotechnologies with biotechnology,information and cognitive sciences could be used forradical human enhancement. If these possibilities wereever realised they would raise profound ethicalquestions.
30 A number of the social and ethical issues thatmight be generated by developments in nanoscienceand nanotechnologies should be investigated furtherand we recommend that the research councils and the
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Arts and Humanities Research Board fund amultidisciplinary research programme to do this. Wealso recommend that the ethical and social implicationsof advanced technologies form part of the formaltraining of all research students and staff working inthese areas.
Stakeholder and public dialogue
31 Public attitudes can play a crucial role in realisingthe potential of technological advances. Public aware-ness of nanotechnologies is low in Great Britain. In thesurvey of public opinion that we commissioned, only29% said they had heard of nanotechnology and only19% could offer any form of definition. Of those whocould offer a definition, 68% felt that it would improvelife in the future, compared to only 4% who thought itwould make life worse.
32 In two in-depth workshops involving small groupsof the general public, participants identified bothpositive and negative potentials in nanotechnologies.Positive views were expressed about new advances in anexciting field; potential applications particularly inmedicine; the creation of new materials; a sense thatthe developments were part of natural progress and thehope that they would improve the quality of life.Concerns were about financial implications; impacts onsociety; the reliability of new applications; long-termside-effects and whether the technologies could becontrolled. The issue of the governance ofnanotechnologies was also raised. Which institutionscould be trusted to ensure that the trajectories ofdevelopment of nanotechnologies are sociallybeneficial? Comparisons were made with geneticallymodified organisms and nuclear power.
33 We recommend that the research councils buildupon our preliminary research into public attitudes byfunding a more sustained and extensive programmeinvolving members of the general public and membersof interested sections of society.
34 We believe that a constructive and proactive debateabout the future of nanotechnologies should beundertaken now at a stage when it can inform keydecisions about their development and before deeplyentrenched or polarised positions appear. Werecommend that the Government initiate adequatelyfunded public dialogue around the development ofnanotechnologies. The precise method of dialogue andchoice of sponsors should be designed around theagreed objectives of the dialogue. Our public attitudeswork suggests that governance would be anappropriate subject for initial dialogue and given thatthe Research Councils are currently funding researchinto nanotechnologies they should consider taking thisforward.
35 A key issue arising from our discussions with thevarious stakeholders was how society can control thedevelopment and deployment of nanotechnologies tomaximise desirable outcomes and keep undesirableoutcomes to an acceptable minimum in other words,how nanotechnologies should be regulated. Theevidence suggests that at present regulatoryframeworks at EU and UK level are sufficiently broadand flexible to handle nanotechnologies at their currentstage of development. However some regulations willneed to be modified on a precautionary basis to reflectthe fact that the toxicity of chemicals in the form of freenanoparticles and nanotubes cannot be predicted fromtheir toxicity in a larger form and that in some casesthey will be more toxic than the same mass of the samechemical in larger form. We looked at a small number ofareas of regulation that cover situations where exposureto nanoparticles or nanotubes is likely currently or in thenear future.
36 Currently the main source of inhalation exposure tomanufactured nanoparticles and nanotubes is inlaboratories and a few other workplaces. Werecommend that the Health and Safety Executive carryout a review of the adequacy of existing regulation toassess and control workplace exposure to nanoparticlesand nanotubes including those relating to accidentalrelease. In the meantime they should consider settinglower occupational exposure levels for chemicals whenproduced in this size range.
37 Under current UK chemical regulation (Notificationof New Substances) and its proposed replacement beingnegotiated at European level (Registration, Evaluationand Authorisation of Chemicals) the production of anexisting substance in nanoparticulate form does nottrigger additional testing. We recommend thatchemicals produced in the form of nanoparticles andnanotubes be treated as new chemicals under theseregulatory frameworks. The annual productionthresholds that trigger testing and the testingmethodologies relating to substances in these sizes,should be reviewed as more toxicological evidencebecomes available.
38 Under cosmetics regulations in the EuropeanUnion, ingredients (including those in the form ofnanoparticles) can be used for most purposes withoutprior approval, provided they are not on the list ofbanned or restricted use chemicals and thatmanufacturers declare the final product to be safe.Given our concerns about the toxicity of anynanoparticles penetrating the skin we recommend thattheir use in products be dependent on a favourableopinion by the relevant European Commission scientificsafety advisory committee. A favourable opinion hasbeen given for the nanoparticulate form of titaniumdioxide (because chemicals used as UV filters must
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undergo an assessment by the advisory committeebefore they can be used) but insufficient informationhas been provided to allow an assessment of zinc oxide.In the meantime we recommend that manufacturerspublish details of the methodologies they have used inassessing the safety of their products containingnanoparticles that demonstrate how they have takenaccount that properties of nanoparticles may bedifferent from larger forms. We do not expect this toapply to many manufacturers since our understanding isthat nanoparticles of zinc oxide are not used extensivelyin cosmetics in Europe. Based on our recommendationthat chemicals produced in the form of nanoparticlesshould be treated as new chemicals, we believe that theingredients lists for consumer products should identifythe fact that manufactured nanoparticles have beenadded. Nanoparticles may be included in moreconsumer products in the future, and we recommendthat the European Commission, with the support of theUK, review the adequacy of the current regulatoryregime with respect to the introduction of nanoparticlesinto any consumer products.
39 Although we think it unlikely that nanoparticles ornanotubes will be released from most materials in whichthey have been fixed, we see any risk of such releasebeing greatest during disposal, destruction or recycling.We therefore recommend that manufacturers ofproducts that fall under extended producerresponsibility regimes such as end-of-life regulationspublish procedures outlining how these materials will bemanaged to minimise possible human andenvironmental exposure.
40 Our review of regulation has not been exhaustiveand we recommend that all relevant regulatory bodiesconsider whether existing regulations are appropriate toprotect humans and the environment from the hazardswe have identified, publish their reviews and explainhow they will address any regulatory gaps. Futureapplications of nanotechnologies may have an impacton other areas of regulation as, for example,developments in sensor technology may haveimplications for legislation relating to privacy. It istherefore important that regulatory bodies includefuture applications of nanotechnologies in their horizon-scanning programmes to ensure that any regulatorygaps are identified at an appropriate stage.
41 Overall, given appropriate regulation and researchalong the lines just indicated, we see no case for themoratorium which some have advocated on thelaboratory or commercial production of manufacturednanomaterials.
Ensuring the responsible development of newand emerging technologies
42 Nanoscience and nanotechnologies are evolvingrapidly, and the pressures of international competitionwill ensure that this will continue. The UK GovernmentsChief Scientific Adviser should therefore commission anindependent group in two years time, and again in fiveyears time, to review what action has been taken as aresult of our recommendations, to assess hownanoscience and nanotechnologies have developed inthe interim, and to consider the ethical, social, health,environmental, safety and regulatory implications ofthese developments. This group should includerepresentatives of, and consult with, the relevantstakeholder groups.
43 More generally, this study has highlighted again thevalue of identifying as early as possible new areas ofscience and technology that have the potential toimpact strongly on society. The Chief Scientific Advisershould therefore establish a group that brings togetherrepresentatives of a wide range of stakeholders to meetbi-annually to review new and emerging technologies,to identify at the earliest possible stage areas whereissues needing Government attention may arise, and toadvise on how these might be addressed. The work ofthis group should be made public and all stakeholdersshould be encouraged to engage with the emergingissues. We expect this group to draw upon the work ofthe other bodies across Government with horizon-scanning roles rather than to duplicate their work.
44 We look forward to the response to this reportfrom the UK Government and from the other parties atwhom the recommendations are targeted. This studyhas generated a great deal of interest among a widerange of stakeholders, both within the UK andinternationally. As far as we are aware it is the first studyof its kind, and we expect its findings to contribute tothe responsible development of nanoscience andnanotechnology globally.
1.1 Hopes and concerns about nanoscienceand nanotechnologies
1 Nanoscience and nanotechnologies are widely seenas having huge potential to bring benefits in areas asdiverse as drug development, water decontamination,information and communication technologies, and theproduction of stronger, lighter materials. They areattracting rapidly increasing investments fromgovernments and from businesses in many parts of theworld; it has been estimated that total global investmentin nanotechnologies is currently around 5 billion, 2 billion of which comes from private sources(European Commission 2004a) (see also Table 1.1). The number of published patents in nanotechnologyincreased fourfold from 1995 (531 parents) to 2001(1976 patents) (3i 2002). Although it is too early toproduce reliable figures for the global market, onewidely quoted estimate puts the annual value for allnanotechnologies-related products (includinginformation and communication technologies) at $1 trillion by 20112015 (NSF 2001). Although manypeople believe that nanotechnologies will have animpact across a wide range of sectors, a survey ofexperts in nanotechnologies across the world identifiedhype (misguided promises that nanotechnology can fixeverything) as the factor most likely to result in abacklash against it (3i 2002).
2 Against this background of increased researchfunding and interest from industry, several non-governmental organizations (NGOs) and somenanotechnologists have expressed concerns aboutcurrent and potential future developments ofnanotechnology. These include uncertainties about theimpact of new nanomaterials on human health,
questions about the type of applications that could arisefrom the expected convergence, in the longer term, ofnanotechnologies with technologies such asbiotechnology, information technology (IT) and artificialintelligence, and suggestions that future developmentsmight bring self-replicating nano-robots that mightdevastate the world (Joy 2000; ETC 2003a). Others havequestioned the adequacy of current regulatoryframeworks to deal with these new developments, andwhether applications will benefit or disenfranchisedeveloping countries (Arnall 2003).
3 The media has reflected the hopes and concernsabout nanoscience and nanotechnology.
4 In January 2003 the Better Regulation Task Force(BRTF) published its report Scientific Research:Innovation with Controls (Better Regulation Task Force2003), which included a consideration ofnanotechnologies. Its first recommendation was that theUK Government should enable the public, throughdebate, to consider the risks of nanotechnologies forthemselves. Other recommendations advocatedopenness in decision making, involving the public in thedecision-making process, developing two-waycommunication channels and taking a strong lead overthe handling of any issues of risk to emerge fromnanotechnologies. In its response to the firstrecommendation, the Government stated that therewas currently no obvious focus for an informed debate,but that it was initiating work that would examinewhether there were any areas of nanotechnology whichraise or will raise specific safety, environmental or ethicalissues that would warrant further study (UKGovernment 2003).
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Table 1.1 Examples of public funding for research and development (R&D) in nanoscience and nanotechnology(source: European Commission 2004a).
Country Expenditure on nanoscience and nanotechnologies
Europe Current funding for nanotechnology R&D is about 1 billion euros, two-thirds of which comesfrom national and regional programmes.
Japan Funding rose from $400M in 2001 to $800M in 2003 and is expected to rise by a further 20%in 2004.
USA The USAs 21st Century Nanotechnology Research and Development Act (passed in 2003)allocated nearly $3.7 billion to nanotechnology from 2005 to 2008 (which excludes asubstantial defence-related expenditure). This compares with $750M in 2003.
UK With the launch of its nanotechnology strategy in 2003, the UK Government pledged 45Mper year from 2003 to 2009.
1.2 Terms of reference and conduct of thestudy
5 In June 2003, following its response to the BRTF,the UK Government commissioned the Royal Societyand the Royal Academy of Engineering (the UKsnational academies of science and of engineering,respectively) to conduct an independent study onnanotechnology. The terms of reference of our study,jointly agreed by the Office of Science and Technologyand the two Academies, were as follows:
define what is meant by nanoscience andnanotechnology;
summarise the current state of scientific knowledgeabout nanotechnology;
identify the specific applications of the newtechnologies, in particular where nanotechnology isalready in use;
carry out a forward look to see how the technologymight be used in future, where possible estimating thelikely time-scales in which the most far-reachingapplications of the technology might become reality;
identify what environmental, health and safety, ethicalor societal implications or uncertainties may arise fromthe use of the technology, both current and future;
identify areas where regulation needs to be considered.
6 The two academies convened a multidisciplinaryworking group of experts in science and engineering,medicine, social science, consumer affairs, ethical issuesand the environment to conduct this study (see Annex Afor a list of Working Group members). The study wasconducted independently of Government, which wasnot involved in the selection of the working groupmembers or its methods of working, and which did notview the report before it was printed. We received muchwritten evidence, and we held a series of oral evidencesessions and workshops with a range of stakeholdersfrom the UK and overseas. The volume of evidence thatwas sent in for the Working Group to consider andfollow up extended the time taken to complete thisproject beyond that originally anticipated. At the outsetof the study it was agreed that the report should includepublic concerns and that data should be collected aboutpublic awareness of nanotechnology, which could formimportant baseline data. The market research companyBMRB International was commissioned to researchpublic attitudes to nanotechnology, which took theform of two workshops and a short market survey. Theevidence was published as the project progressed andcomments were invited through a dedicated website(www.nanotec.org.uk). A detailed description of the
conduct of the study can be found in Annex B. We areextremely grateful to all those organisations andindividuals who contributed to the study; they are listedin Annex C. Their contributions can be found on ourwebsite and are available on the CD at the back of thehardcopy version of this report. In the report thesecontributions have been referred to as evidence. Thereport was peer reviewed by a small group of Fellowsfrom the two academies (listed in Annex A) beforebeing considered by the two academies. It has beenendorsed by the Council of the Royal Society andapproved for publication by the Royal Academy ofEngineering.
1.3 Report overview
7 In Chapter 2 we introduce nanoscience andnanotechnologies, and explain the definitions of eachthat we used during the study. In Chapter 3 we giveexamples of key current research, and current andpotential future advances in: nanomaterials;nanometrology; electronics, optoelectronics and ICT;and bio-nanotechnology. We also look at the benefitsthey are currently providing and might provide in theshort, medium and longer term. In Chapter 4 we look atcurrent and possible future industrial applications ofnanotechnology, and examine some of the barriers to itstake-up by industry. In Chapters 3 and 4 we haveprovided an overview (rather than a detailedassessment) of current and potential futuredevelopments in, and applications of, nanoscience andnanotechnologies, against which health, safety,environmental, social and ethical implications (addressedlater in the report) could be considered. The Taylorreport (DTI 2002) reviewed the state of nanotechnologyapplications in industry in the UK and proposed a seriesof actions to accelerate and support increased industrialinvestment in the exploitation of nanotechnology in theUK. It was not our intention to critique or update theTaylor report or to identify research priorities fornanoscience and nanotechnology. The House ofCommons Science and Technology Committee hasrecently evaluated the implementation of therecommendations of the Taylor report (House ofCommons 2004a).
8 In Chapter 5 we evaluate the potential health, safetyand environmental implications of nanotechnologies,and in Chapter 6 we consider the potential social andethical implications. In both chapters we identify themain gaps in knowledge related to the potential impactsof nanotechnologies. Chapter 7 outlines the results ofour commissioned research into public attitudes tonanotechnology in Great Britain, and considers the roleof multi-stakeholder dialogue in the future developmentof nanotechnologies. The implications of ourconclusions for the current regulatory framework are
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outlined in Chapter 8. Finally, Chapters 9 and 10contain our overall conclusions and list ourrecommendations.
1.4 Next steps
9 We look forward to the response to this reportfrom the UK Government and from the other parties atwhom the recommendations are targeted. This studyhas generated a great deal of interest among a widerange of stakeholders, both within the UK and
internationally. As far as we are aware it is the first studyof its kind, and we expect its findings to contribute tothe responsible development of nanoscience andnanotechnology globally. The two academies willcontinue to participate in this important area. The issuesraised and conclusions reached in this report can bedebated through the discussion section of the dedicatedwebsite (www.nanotec.org.uk). We will hold an openmeeting in London to discuss the reports findingsshortly after its publication.
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l & D
1 The first term of reference of this study was to definewhat is meant by nanoscience and nanotechnology.However, as the term nanotechnology encompassessuch a wide range of tools, techniques and potentialapplications, we have found it more appropriate to referto nanotechnologies. Our definitions were developedthrough consultation at our workshop meeting withscientists and engineers and through commentsreceived through the study website.
2 Although there is no sharp distinction betweenthem, in this report we differentiate betweennanoscience and nanotechnologies as follows.
3 The prefix nano is derived from the Greek wordfor dwarf. One nanometre (nm) is equal to one-billionthof a metre, 109m. A human hair is approximately80,000nm wide, and a red blood cell approximately 7000nm wide. Figure 2.1 shows the nanometre incontext. Atoms are below a nanometre in size, whereasmany molecules, including some proteins, range from ananometre upwards.
4 The conceptual underpinnings of nanotechnologieswere first laid out in 1959 by the physicist RichardFeynman, in his lecture Theres plenty of room at thebottom (Feynman 1959). Feynman explored thepossibility of manipulating material at the scale ofindividual atoms and molecules, imagining the whole ofthe Encyclopaedia Britannica written on the head of apin and foreseeing the increasing ability to examine andcontrol matter at the nanoscale.
5 The term nanotechnology was not used until1974, when Norio Taniguchi, a researcher at theUniversity of Tokyo, Japan used it to refer to the abilityto engineer materials precisely at the nanometre level(Taniguchi 1974). The primary driving force forminiaturisation at that time came from the electronicsindustry, which aimed to develop tools to create smaller(and therefore faster and more complex) electronicdevices on silicon chips. Indeed, at IBM in the USA a
technique called electron beam lithography was used tocreate nanostructures and devices as small as 4070nmin the early 1970s.
6. The size range that holds so much interest istypically from 100nm down to the atomic level(approximately 0.2nm), because it is in this range(particularly at the lower end) that materials can havedifferent or enhanced properties compared with thesame materials at a larger size. The two main reasonsfor this change in behaviour are an increased relativesurface area, and the dominance of quantum effects.An increase in surface area (per unit mass) will result ina corresponding increase in chemical reactivity, makingsome nanomaterials useful as catalysts to improve theefficiency of fuel cells and batteries. As the size ofmatter is reduced to tens of nanometres or less,quantum effects can begin to play a role, and these cansignificantly change a materials optical, magnetic orelectrical properties. In some cases, size-dependentproperties have been exploited for centuries. Forexample, gold and silver nanoparticles (particles ofdiameter less than 100 nm; see section 3.2) have beenused as coloured pigments in stained glass and ceramicssince the 10th century AD (Erhardt 2003). Depending ontheir size, gold particles can appear red, blue or gold incolour. The challenge for the ancient (al)chemists was tomake all nanoparticles the same size (and hence thesame colour), and the production of single-sizenanoparticles is still a challenge today.
7. At the larger end of our size range, other effectssuch as surface tension or stickiness are important,which also affect physical and chemical properties. Forliquid or gaseous environments Brownian motion, whichdescribes the random movement of larger particles ormolecules owing to their bombardment by smallermolecules and atoms, is also important. This effectmakes control of individual atoms or molecules in theseenvironments extremely difficult.
8. Nanoscience is concerned with understandingthese effects and their influence on the properties ofmaterial. Nanotechnologies aim to exploit these effectsto create structures, devices and systems with novelproperties and functions due to their size.
9. In some senses, nanoscience and nanotechnologiesare not new. Many chemicals and chemical processeshave nanoscale features for example, chemists havebeen making polymers, large molecules made up of tinynanoscalar subunits, for many decades.Nanotechnologies have been used to create the tinyfeatures on computer chips for the past 20 years. Thenatural world also contains many examples of nanoscalestructures, from milk (a nanoscale colloid) tosophisticated nanosized and nanostructured proteins
Box 2.1 Definitions of nanoscience and nanotechnologies
Nanoscience is the study of phenomena andmanipulation of materials at atomic, molecular andmacromolecular scales, where properties differsignificantly from those at a larger scale.
Nanotechnologies are the design, characterisation,production and application of structures, devices andsystems by controlling shape and size at nanometrescale.
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2 What are nanoscience and nanotechnologies?
that control a range of biological activities, such asflexing muscles, releasing energy and repairing cells.Nanoparticles occur naturally, and have been created forthousands of years as the products of combustion andfood cooking.
10 However, it is only in recent years that sophisticatedtools have been developed to investigate andmanipulate matter at the nanoscale, which have greatlyaffected our understanding of the nanoscale world. Amajor step in this direction was the invention of thescanning tunnelling microscope (STM) in 1982, and theatomic force microscope (AFM) in 1986. These tools usenanoscale probes to image a surface with atomicresolution, and are also capable of picking up, sliding ordragging atoms or molecules around on surfaces tobuild rudimentary nanostructures. These tools arefurther described in Box 3.1. In a now famousexperiment in 1990, Don Eigler and Erhard Schweizer atIBM moved xenon atoms around on a nickel surface towrite the company logo (Eigler and Schweizer 1990)(see Figure 2.1), a laborious process which took a wholeday under well-controlled conditions. The use of thesetools is not restricted to engineering, but has beenadopted across a range of disciplines. AFM, for example,is routinely used to study biological molecules such asproteins.
11 The technique used by Eigler and Schweizer is onlyone in the range of ways used to manipulate andproduce nanomaterials, commonly categorised as eithertop-down or bottom-up. Top-down techniquesinvolve starting with a block of material, and etching ormilling it down to the desired shape, whereas bottom-
up involves the assembly of smaller sub-units (atoms ormolecules) to make a larger structure. The mainchallenge for top-down manufacture is the creation ofincreasingly small structures with sufficient accuracy,whereas for bottom-up manufacture, it is to makestructures large enough, and of sufficient quality, to beof use as materials. These two methods have evolvedseparately and have now reached the point where thebest achievable feature size for each technique isapproximately the same, leading to novel hybrid ways ofmanufacture.
12 Nanotechnologies can be regarded as genuinelyinterdisciplinary, and have prompted the collaborationbetween researchers in previously disparate areas toshare knowledge, tools and techniques. Anunderstanding of the physics and chemistry of matterand processes at the nanoscale is relevant to all scientificdisciplines, from chemistry and physics to biology,engineering and medicine. Indeed, it could be arguedthat evolutionary developments in each of these fieldstowards investigating matter at increasingly small sizescales has now come to be known as nanotechnology.
13 It will be seen in Chapters 3 and 4 that nanoscienceand nanotechnologies encompass a broad and variedrange of materials, tools and approaches. Apart from acharacteristic size scale, it is difficult to findcommonalities between them. We should not thereforeexpect them to have the same the same health,environmental, safety, social or ethical implications orrequire the same approach to regulation; these issuesare dealt with in Chapters 5 8.
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3 Science and applications
1 In this chapter we provide an overview of some keycurrent developments in nanoscience andnanotechnologies, and highlight some possible futureapplications. The chapter is informed by evidence fromscientists and engineers in academia and industry. Itillustrates the wide-ranging interest in these areas andprovides a background to the later chapters, whichaddress health, environmental, social, ethical andregulatory implications of nanotechnologies. It does notconsider in detail the developments in nanoscience andnanotechnologies in all scientific and engineering fields.
2 As nanoscience and nanotechnologies cover such awide range of fields (from chemistry, physics andbiology, to medicine, engineering and electronics), wehave considered them in four broad categories:nanomaterials; nanometrology; electronics,optoelectronics and information and communicationtechnology; and bio-nanotechnology andnanomedicine. This division helps to distinguishbetween developments in different fields, but there isnaturally some overlap.
3 Where possible, we define the development offuture applications as short term (under 5years),medium term (515 years), and long term (over20years). It may be that some of the potentialapplications that we identify are never realised, whereasothers that are currently unforeseen could have a majorimpact. We also identify potential in environmental,health and safety, ethical or societal implications oruncertainties that are discussed further in later chapters.
4 Current industrial applications of nanotechnologiesare dealt with in Chapter 4, as are the factors that willinfluence their application in the future.
3.2.1 Introduction to nanomaterials
5 A key driver in the development of new andimproved materials, from the steels of the 19th centuryto the advanced materials of today, has been the abilityto control their structure at smaller and smaller scales.The overall properties of materials as diverse as paintsand silicon chips are determined by their structure at themicro- and nanoscales. As our understanding ofmaterials at the nanoscale and our ability to controltheir structure improves, there will be great potential tocreate a range of materials with novel characteristics,functions and applications.
6 Although a broad definition, we categorisenanomaterials as those which have structuredcomponents with at least one dimension less than100nm. Materials that have one dimension in thenanoscale (and are extended in the other two dimensions)are layers, such as a thin films or surface coatings. Someof the features on computer chips come in this category.Materials that are nanoscale in two dimensions (andextended in one dimension) include nanowires andnanotubes. Materials that are nanoscale in threedimensions are particles, for example precipitates, colloidsand quantum dots (tiny particles of semiconductormaterials). Nanocrystalline materials, made up ofnanometre-sized grains, also fall into this category. Someof these materials have been available for some time;others are genuinely new. The aim of this chapter is togive an overview of the properties, and the significantforeseeable applications of some key nanomaterials.
7 Two principal factors cause the properties ofnanomaterials to differ significantly from othermaterials: increased relative surface area, and quantumeffects. These factors can change or enhance propertiessuch as reactivity, strength and electrical characteristics.As a particle decreases in size, a greater proportion ofatoms are found at the surface compared to thoseinside. For example, a particle of size 30 nm has 5% ofits atoms on its surface, at 10 nm 20% of its atoms, andat 3 nm 50% of its atoms. Thus nanoparticles have amuch greater surface area per unit mass compared withlarger particles. As growth and catalytic chemicalreactions occur at surfaces, this means that a given massof material in nanoparticulate form will be much morereactive than the same mass of material made up oflarger particles.
8 In tandem with surface-area effects, quantumeffects can begin to dominate the properties of matteras size is reduced to the nanoscale. These can affect theoptical, electrical and magnetic behaviour of materials,particularly as the structure or particle size approachesthe smaller end of the nanoscale. Materials that exploitthese effects include quantum dots, and quantum welllasers for optoelectronics.
9 For other materials such as crystalline solids, as thesize of their structural components decreases, there ismuch greater interface area within the material; this cangreatly affect both mechanical and electrical properties.For example, most metals are made up of smallcrystalline grains; the boundaries between the grainslow down or arrest the propagation of defects whenthe material is stressed, thus giving it strength. If thesegrains can be made very small, or even nanoscale insize, the interface area within the material greatly
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increases, which enhances its strength. For example,nanocrystalline nickel is as strong as hardened steel.Understanding surfaces and interfaces is a key challengefor those working on nanomaterials, and one wherenew imaging and analysis instruments are vital.
10 Nanomaterials are not simply another step in theminiaturization of materials. They often require verydifferent production approaches. As introduced inChapter 2, and discussed further in Chapter 4, there areseveral processes to create nanomaterials, classified astop-down and bottom-up. Although manynanomaterials are currently at the laboratory stage ofmanufacture, a few of them are being commercialised.
3.2.2 Nanoscience in this area
11 Below we outline some examples of nanomaterialsand the range of nanoscience that is aimed atunderstanding their properties. As will be seen, thebehaviour of some nanomaterials is well understood,whereas others present greater challenges.
a) Nanoscale in one dimension
Thin films, layers and surfaces12 One-dimensional nanomaterials, such as thin filmsand engineered surfaces, have been developed andused for decades in fields such as electronic devicemanufacture, chemistry and engineering. In the siliconintegrated-circuit industry, for example, many devicesrely on thin films for their operation, and control of filmthicknesses approaching the atomic level is routine.Monolayers (layers that are one atom or molecule deep)are also routinely made and used in chemistry. Theformation and properties of these layers are reasonablywell understood from the atomic level upwards, even inquite complex layers (such as lubricants). Advances arebeing made in the control of the composition andsmoothness of surfaces, and the growth of films.
13 Engineered surfaces with tailored properties such aslarge surface area or specific reactivity are used routinelyin a range of applications such as in fuel cells andcatalysts (see section 3.2.3b). The large surface areaprovided by nanoparticles, together with their ability toself assemble on a support surface, could be of use in allof these applications.
14 Although they represent incremental developments,surfaces with enhanced properties should find applicationsthroughout the chemicals and energy sectors. Thebenefits could surpass the obvious economic andresource savings achieved by higher activity and greaterselectivity in reactors and separation processes, toenabling small-scale distributed processing (makingchemicals as close as possible to the point of use). Thereis already a move in the chemical industry towards this.Another use could be the small-scale, on-site productionof high value chemicals such as pharmaceuticals.
b) Nanoscale in two dimensions
15 Two dimensional nanomaterials such as tubes andwires have generated considerable interest among thescientific community in recent years. In particular, theirnovel electrical and mechanical properties are thesubject of intense research.
Carbon nanotubes16 Carbon nanotubes (CNTs) were first observed bySumio Iijima in 1991 (Iijima 1991). CNTs are extendedtubes of rolled graphene sheets. There are two types ofCNT: single-walled (one tube) or multi-walled (severalconcentric tubes) (Figure 3.1). Both of these are typicallya few nanometres in diameter and several micrometres (10-6m) to centimetres long. CNTs have assumed animportant role in the context of nanomaterials, becauseof their novel chemical and physical properties. They aremechanically very strong (their Youngs modulus is over1 terapascal, making CNTs as stiff as diamond), flexible(about their axis), and can conduct electricity extremelywell (the helicity of the graphene sheet determineswhether the CNT is a semiconductor or metallic). All ofthese remarkable properties give CNTs a range ofpotential applications: for example, in reinforcedcomposites, sensors, nanoelectronics and displaydevices.
Figure 3.1a Schematic of a single-walled carbon nanotube (SWNT)
Figure 3.1b Schematic of a multi-walled carbon nanotube (MWNT)
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17 CNTs are now available commercially in limitedquantities. They can be grown by several techniques,which are discussed in section 4.3.1b. However, theselective and uniform production of CNTs with specificdimensions and physical properties is yet to be achieved.The potential similarity in size and shape between CNTsand asbestos fibres has led to concerns about their safety,which we address in detail in sections 5.3.1b and 5.3.2a.
Inorganic nanotubes18 Inorganic nanotubes and inorganic fullerene-likematerials based on layered compounds such asmolybdenum disulphide were discovered shortly afterCNTs. They have excellent tribological (lubricating)properties, resistance to shockwave impact, catalyticreactivity, and high capacity for hydrogen and lithiumstorage, which suggest a range of promisingapplications. Oxide-based nanotubes (such as titaniumdioxide) are being explored for their applications incatalysis, photo-catalysis and energy storage.
Nanowires19 Nanowires are ultrafine wires or linear arrays ofdots, formed by self-assembly. They can be made from awide range of materials. Semiconductor nanowiresmade of silicon, gallium nitride and indium phosphidehave demonstrated remarkable optical, electronic andmagnetic characteristics (for example, silica nanowirescan bend light around very tight corners). Nanowireshave potential applications in high-density data storage,either as magnetic read heads or as patterned storagemedia, and electronic and opto-electronic nanodevices,for metallic interconnects of quantum devices andnanodevices. The preparation of these nanowires relieson sophisticated growth techniques, which include self-assembly processes, where atoms arrange themselvesnaturally on stepped surfaces, chemical vapourdeposition (CVD) onto patterned substrates,electroplating or molecular beam epitaxy (MBE). Themolecular beams are typically from thermallyevaporated elemental sources.
Biopolymers20 The variability and site recognition of biopolymers,such as DNA molecules, offer a wide range ofopportunities for the self-organization of wirenanostructures into much more complex patterns. TheDNA backbones may then, for example, be coated inmetal. They also offer opportunities to link nano- andbiotechnology in, for example, biocompatible sensorsand small, simple motors. Such self-assembly of organicbackbone nanostructures is often controlled by weakinteractions, such as hydrogen bonds, hydrophobic, orvan der Waals interactions (generally in aqueousenvironments) and hence requires quite differentsynthesis strategies to CNTs, for example. Thecombination of one-dimensional nanostructuresconsisting of biopolymers and inorganic compoundsopens up a number of scientific and technologicalopportunities.
c) Nanoscale in three dimensions
Nanoparticles21 Nanoparticles are often defined as particles of lessthan 100nm in diameter. In line with our definitions ofnanoscience and nanotechnologies (see Box 2.1), weclassify nanoparticles to be particles less than 100nm indiameter that exhibit new or enhanced size-dependentproperties compared with larger particles of the samematerial. Nanoparticles exist widely in the natural world:for example as the products of photochemical andvolcanic activity, and created by plants and algae. Theyhave also been created for thousands of years asproducts of combustion and food cooking, and morerecently from vehicle exhausts. Deliberatelymanufactured nanoparticles, such as metal oxides, areby comparison in the minority. In this report we willrefer to these as natural, pollutant and manufacturednanoparticles, respectively.
22 As described in Chapter 2, nanoparticles are ofinterest because of the new properties (such as chemicalreactivity and optical behaviour) that they exhibitcompared with larger particles of the same materials.For example, titanium dioxide and zinc oxide becometransparent at the nanoscale, however are able toabsorb and reflect UV light, and have found applicationin sunscreens. Nanoparticles have a range of potentialapplications: in the short-term in new cosmetics, textilesand paints; in the longer term, in methods of targeteddrug delivery where they could be to used deliver drugsto a specific site in the body. Nanoparticles can also bearranged into layers on surfaces, providing a largesurface area and hence enhanced activity, relevant to arange of potential applications such as catalysts.
23 Manufactured nanoparticles are typically notproducts in their own right, but generally serve as rawmaterials, ingredients or additives in existing products.Although their production is currently low comparedwith other nanomaterials we have given them aconsiderable amount of attention in this report. This isbecause they are currently in a small number ofconsumer products such as cosmetics and theirenhanced or novel properties may have implications fortheir toxicity. The evidence submitted during the courseof our study indicates that for most applications,nanoparticles will be fixed (for example, attached to asurface or within in a composite) although in othersthey will be free or suspended in fluid. Whether they arefixed or free will have a significant affect on theirpotential health, safety and environmental impacts. Weaddress these issues in detail in Chapter 5.
Fullerenes (carbon 60)24 In the mid-1980s a new class of carbon material wasdiscovered called carbon 60 (C60) (Kroto et al 1985). Adiagram of carbon 60 can be found in Figure 2.1. Theseare spherical molecules about 1nm in diameter,comprising 60 carbon atoms arranged as 20 hexagons
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and 12 pentagons: the configuration of a football. TheC60 species was named Buckminsterfullerene inrecognition of the architect Buckminster Fuller, who waswell-known for building geodesic domes, and the termfullerenes was then given to any closed carbon cage. In1990, a technique to produce larger quantities of C60 wasdeveloped by resistively heating graphite rods in a heliumatmosphere (Krtschmer et al 1990). Several applicationsare envisaged for fullerenes, such as miniature ballbearings to lubricate surfaces, drug delivery vehicles andin electronic circuits.
Dendrimers25 Dendrimers are spherical polymeric molecules,formed through a nanoscale hierarchical self-assemblyprocess. There are many types of dendrimer; the smallestis several nanometres in size. Dendrimers are used inconventional applications such as coatings and inks, butthey also have a range of interesting properties whichcould lead to useful applications. For example,dendrimers can act as nanoscale carrier molecules andas such could be used in drug delivery. Environmentalclean-up could be assisted by dendrimers as they cantrap metal ions, which could then be filtered out ofwater with ultra-filtration techniques.
Quantum dots26 Nanoparticles of semiconductors (quantum dots)were theorized in the 1970s and initially created in theearly 1980s. If semiconductor particles are made smallenough, quantum effects come into play, which limitthe energies at which electrons and holes (the absenceof an electron) can exist in the particles. As energy isrelated to wavelength (or colour), this means that theoptical properties of the particle can be finely tuneddepending on its size. Thus, particles can be made toemit or absorb specific wavelengths (colours) of light,merely by controlling their size. Recently, quantum dotshave found applications in composites, solar cells(Gratzel cells) and fluorescent biological labels (forexample to trace a biological molecule) which use boththe small particle size and tuneable energy levels.Recent advances in chemistry have resulted in thepreparation of monolayer-protected, high-quality,monodispersed, crystalline quantum dots as small as2nm in diameter, which can be conveniently treatedand processed as a typical chemical reagent.
27 Below we list some key current and potential short-and long-term applications of nanomaterials. Mostcurrent applications represent evolutionarydevelopments of existing technologies: for example, thereduction in size of electronics devices.
Sunscreens and cosmetics28 Nanosized titanium dioxide and zinc oxide are
currently used in some sunscreens, as they absorb andreflect ultraviolet (UV) rays and yet are transparent tovisible light and so are more appealing to the consumer.Nanosized iron oxide is present in some lipsticks as apigment but it is our understanding that it is not usedby the European cosmetics sector. The use ofnanoparticles in cosmetics has raised a number ofconcerns about consumer safety; we evaluate theevidence relating to these concerns in section 5.3.2b.
Composites29 An important use of nanoparticles and nanotubesis in composites, materials that combine one or moreseparate components and which are designed to exhibitoverall the best properties of each component. Thismulti-functionality applies not only to mechanicalproperties, but extends to optical, electrical andmagnetic ones. Currently, carbon fibres and bundles ofmulti-walled CNTs are used in polymers to control orenhance conductivity, with applications such as anti-static packaging. The use of individual CNTs incomposites is a potential long-term application (seesection 3.2.3c). A particular type of nanocomposite iswhere nanoparticles act as fillers in a matrix; forexample, carbon black used as a filler to reinforce cartyres. However, particles of carbon black can range fromtens to hundreds of nanometres in size, so not allcarbon black falls within our definition of nanoparticles.
Clays30 Clays containing naturally occurring nanoparticleshave long been important as construction materials andare undergoing continuous improvement. Clay particlebased composites containing plastics and nano-sizedflakes of clay are also finding applications such as usein car bumpers.
Coatings and surfaces31 Coatings with thickness controlled at the nano- oratomic scale have been in routine production for sometime, for example in MBE or metal oxide CVD foroptoelectonic devices, or in catalytically active andchemically functionalized surfaces. Recently developedapplications include the self-cleaning window, which iscoated in highly activated titanium dioxide, engineeredto be highly hydrophobic (water repellent) and anti-bacterial, and coatings based on nanoparticulate oxidesthat catalytically destroy chemical agents (Royal Society2004a). Wear and scratch-resistant hard coatings aresignificantly improved by nanoscale intermediate layers (ormultilayers) between the hard outer layer and thesubstrate material. The intermediate layers give goodbonding and graded matching of elastic and thermalproperties, thus improving adhesion. A range of enhancedtextiles, such as breathable, waterproof and stain-resistant fabrics, have been enabled by the improvedcontrol of porosity at the nanoscale and surfaceroughness in a variety of polymers and inorganics.
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Tougher and harder cutting tools32 Cutting tools made of nanocrystalline materials,such as tungsten carbide, tantalum carbide and titaniumcarbide, are more wear and erosion-resistant, and lastlonger than their conventional (large-grained)counterparts. They are finding applications in the drillsused to bore holes in circuit boards.
Paints33 Incorporating nanoparticles in paints could improvetheir performance, for example by making them lighterand giving them different properties. Thinner paintcoatings (lightweighting), used for example on aircraft,would reduce their weight, which could be beneficial tothe environment. However, the whole life cycle of theaircraft needs to be considered before overall benefitscan be claimed (see section 4.5). It may also be possibleto substantially reduce solvent content of paints, withresulting environmental benefits. New types of fouling-resistant marine paint could be developed and areurgently needed as alternatives to tributyl tin (TBT), nowthat the ecological impacts of TBT have beenrecognised. Anti-fouling surface treatment is alsovaluable in process applications such as heat exchange,where it could lead to energy savings. If they can beproduced at sufficiently low cost, fouling-resistantcoatings could be used in routine duties such as pipingfor domestic and industrial water systems. It remainsspeculation whether very effective anti-fouling coatingscould reduce the use of biocides, including chlorine.Other novel, and more long-term, applications fornanoparticles might lie in paints that change colour inresponse to change in temperature or chemicalenvironment, or paints that have reduced infra-redabsorptivity and so reduce heat loss.
34 Concerns about the health and environmentalimpacts of nanoparticles (which we address in detail inChapter 5) may require the need for the durability andabrasion behaviour of nano-engineered paints andcoatings to be addressed, so that abrasion products takethe form of coarse or microscopic agglomerates ratherthan individual nanoparticles.
Remediation35 The potential of nanoparticles to react withpollutants in soil and groundwater and transform theminto harmless compounds is being researched. In onepilot study the large surface area and high surfacereactivity of iron nanoparticles were exploited totransform chlorinated hydrocarbons (some of which arebelieved to be carcinogens) into less harmful endproducts in groundwater (Zhang 2003). It is also hopedthat they could be used to transform heavy metals suchas lead and mercury from bioavailable forms intoinsoluble forms. Serious concerns have been raised overthe uncontrolled release of nanoparticles into theenvironment; these are discussed in section 5.4.
Fuel Cells36 Engineered surfaces are essential in fuel cells, wherethe external surface properties and the pore structureaffect performance. The hydrogen used as the immediatefuel in fuel cells may be generated from hydrocarbonsby catalytic reforming, usually in a reactor moduleassociated directly with the fuel cell. The potential useof nano-engineered membranes to intensify catalyticprocesses could enable higher-efficiency, small-scale fuelcells. These could act as distributed sources of electricalpower. It may eventually be possible to producehydrogen locally from sources other than hydrocarbons,which are the feedstocks of current attention.
Displays37 The huge market for large area, high brightness,flat-panel displays, as used in television screens andcomputer monitors, is driving the development of somenanomaterials. Nanocrystalline zinc selenide, zincsulphide, cadmium sulphide and lead telluridesynthesized by solgel techniques (a process for makingceramic and glass materials, involving the transitionfrom a liquid sol phase to a solid gel phase) arecandidates for the next generation of light-emittingphosphors. CNTs are being investigated for low voltagefield-emission displays; their strength, sharpness,conductivity and inertness make them potentially veryefficient and long-lasting emitters.
Batteries38 With the growth in portable electronic equipment(mobile phones, navigation devices, laptop computers,remote sensors), there is great demand for lightweight,high-energy density batteries. Nanocrystalline materialssynthesized by solgel techniques are candidates forseparator plates in batteries because of their foam-like(aerogel) structure, which can hold considerably moreenergy than conventional ones. Nickelmetal hydridebatteries made of nanocrystalline nickel and metalhydrides are envisioned to require less frequentrecharging and to last longer because of their largegrain boundary (surface) area.
Fuel additives39 Research is underway into the addition ofnanoparticulate ceria (cerium oxide) to diesel fuel toimprove fuel economy by reducing the degradation offuel consumption over time (Oxonica 2003).
Catalysts40 In general, nanoparticles have a high surface area,and hence provide higher catalytic activity.Nanotechnologies are enabling changes in the degree ofcontrol in the production of nanoparticles, and thesupport structure on which they reside. It is possible tosynthesise metal nanoparticles in solution in thepresence of a surfactant to form highly orderedmonodisperse films of the catalyst nanoparticles on asurface. This allows more uniformity in the size andchemical structure of the catalyst, which in turn leads to
The Royal Society & The Royal Academy of Engineering Nanoscience and nanotechnologies | July 2004 | 11
greater catalytic activity and the production of fewer by-products. It may also be possible to engineer specific orselective activity. These more active and durablecatalysts could find early application in cleaning upwaste streams. This will be particularly beneficial if itreduces the demand for platinum-group metals, whoseuse in standard catalytic units is starting to emerge as aproblem, given the limited availability of these metals.
c) Longer-term applications
Carbon nanotube composites41 CNTs have exceptional mechanical properties,particularly high tensile strength and light weight. Anobvious area of application would be in nanotube-reinforced composites, with performance beyondcurrent carbon-fibre composites. One current limit tothe introduction of CNTs in composites is the problem ofstructuring the tangle of nanotubes in a well-orderedmanner so that use can be made of their strength.Another challenge is generating strong bondingbetween CNTs and the matrix, to give good overallcomposite performance and retention during wear orerosion of composites. The surfaces of CNTs are smoothand relatively unreactive, and so tend to slip through thematrix when it is stressed. One approach that is beingexplored to prevent this slippage is the attachment ofchemical side-groups to CNTs, effectively to formanchors. Another limiting factor is the cost ofproduction of CNTs. However, the potential benefits ofsuch light, high strength material in numerousapplications for transportation are such that significantfurther research is likely.
Lubricants42 Nanospheres of inorganic materials could be usedas lubricants, in essence by acting as nanosized ballbearings. The controlled shape is claimed to make themmore durable than conventional solid lubricants andwear additives. Whether the increased financial andresource cost of producing them is offset by the longerservice life of lubricants and parts remains to beinvestigated (along the lines of the methodologyoutlined in section 4.5). It is also claimed that thesenanoparticles reduce friction between metal surfaces,particularly at high normal loads. If so, they should findtheir first applications in high-performance engines anddrivers; this could include the energy sector as well astransport. There is a further claim that this type oflubricant is effective even if the metal surfaces are nothighly smooth. Again, the benefits of reduced cost andresource input for machining must be compared againstproduction of nanolubricants. In all these applications,the particles would be dispersed in a conventional liquidlubricant; design of the lubricant system must thereforeinclude measures to contain and manage waste.
Magnetic materials43 It has been shown that magnets made ofnanocrystalline yttriumsamariumcobalt grains possess
unusual magnetic properties due to their extremelylarge grain interface area (high coercivity can beobtained because magnetization flips cannot easilypropagate past the grain boundaries). This could lead toapplications in motors, analytical instruments likemagnetic resonance imaging (MRI), used widely inhospital