Nanochemistry

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Nanochemistry 

Nanochemistry is the combination of chemistry and nano science. Nanochemistry is associated with synthesis of building blocks which are dependent on size, surface, shape and defect properties. Nanochemistry is being used in chemical, materials and physical, science as well as engineering, biological and medical applications. Nanochemistry and other nanoscience fields have the same core concepts but the usages of those concepts are different.

The nano prefix was given to nanochemistry when scientists observed the odd changes on materials when they were in nanometer-scale size. Several chemical modification on nanometer scaled structures, approves effects of being size dependent.

Nanochemistry can be characterized by concepts of size, shape, self-assembly, defects and bio-nano; So the synthesis of any new nano-construct is associated with all these concepts. Nano-construct synthesis is dependent on how the surface, size and shape will lead to self-assembly of the building blocks into the functional structures; they probably have functional defects and might be useful for electronic, photonic, medical or bioanalytical problems.

Silica, gold, polydimethylsiloxane, cadmium selenide, iron oxide and carbon are materials that show the transformative power of nanochemistry. Nanochemistry can make the most effective contrast agent of MRI out of iron oxide (rust) which has the ability of detecting cancers and even killing them at their initial stages. Silica (glass) can be used to bend or stop light in its tracks. Developing countries also use silicone to make the circuits for the fluids to attain developed world's pathogen detection abilities. Carbon has been used in different shapes and forms and it will become a better choice for electronic materials.

Overall, nanochemistry is not related to the atomic structure of compounds. Rather, it is about different ways to transform materials into solutions to solve problems. Chemistry mainly deals with degrees of freedom of atoms in the periodic table however nanochemistry brought other degrees of freedom that controls material's behaviors.

Nanochemical methods can be used to create carbon nanomaterials such as carbon nanotubes (CNT), graphene and fullerenes which have gained attention in recent years due to their remarkable mechanical and electrical properties.

Nanotopography

Nanotopography refers to the specific surface features which appear on the nanoscale. In industry, applications of nanotopography typically encompass electrics and artificially produced surface features. However, natural surface features are also included in this definition, such as molecular-level cell interactions and the textured organs of animals and plants. These nanotopographical features in nature serve distinctive purposes that aid in regulation and function of the biotic organism, as nanotopographical features are extremely sensitive in cells.

Nanolithography

Nanolithography is the process by which nanotopographical etchings are artificially produced on a surface. Many practical applications make use of nanolithography, including semiconductor chips in computers. There are many types of nanolithography, which include:

• Photolithography
• Electron beam lithography (EBL)
• X-ray lithography
• Extreme ultraviolet lithography (EUVL)
• Light coupling nanolithography (LCM)
• Scanning probe microscope lithography (SPM)
• Nanoimprint lithographyh
• Dip-Pen nanolithography
• Soft lithography

Each nanolithography technique has varying factors of resolution, time consumption, and cost. There are three basic methods used by nanolithography. One involves using a resist material which acts as a "mask" to cover and protect the areas of the surface that are intended to be smooth. The uncovered portions can now be etched away, with the protective material acting as a stencil. The second method involves directly carving the desired pattern. Etching may involve using a beam of quantum particles, such as electrons or light, or chemical methods such as oxidation or SAM's (self-assembled monolayers). The third method places the desired pattern directly on the surface, producing a final product that is ultimately a few nanometers thicker than the original surface. In order to visualize the surface to be fabricated, the surface must be visualized by a nano-resolution microscope, which include the scanning probe microscope (SPM) and the atomic force microscope (AFM). Both microscopes can also be engaged in processing the final product.

SAM's

One of the methods of nanolithography is use of self-assembled monolayers (SAM) which develops soft methodology. SAMs are long chain alkanethiolates that are self-assembled on gold surfaces making a well-ordered monolayer films. The advantage of this method is to create a high quality structure with lateral dimensions of 5 nm to 500 nm. In this methodology a patterned elastomer made of polydimethylsiloxane (PDMS) as a mask is usually used. In order to make a PDMS stamp, the first step is to coat a thin layer of photoresist onto a silicon wafer. The next step is to expose the layer with UV light, and the exposed photoresist is washed away with developer. In order to reduce the thickness of the prepolymer, the patterned master is treated with perfluoroalkyltrichlorosilane. These PDMS elastomers are used to print micron and submicron design chemical inks on both planar and curved surfaces for different purposes.

Applications

Medicine

One highly researched application of nanochemistry is medicine. A simple skin-care product using the technology of nanochemistry is sunscreen. Sunscreen contains nanoparticles of zinc oxide and titanium dioxide. These nanochemicals protect the skin against harmful UV light by absorbing or reflecting the light and prevent the skin from retaining full damage by photoexcitation of electrons in the nanoparticle. Effectively, the excitation of the particle blocks skin cells from DNA damage.

Drug delivery

Emerging methods of drug delivery involving nanotechnological methods can be advantageous by improving increased bodily response, specific targeting, and efficient, non-toxic metabolism. Many nanotechnological methods and materials can be functionalized for drug delivery. Ideal materials employ a controlled-activation nanomaterial to carry a drug cargo into the body. Mesoporous silica nanoparticles (MSN) have been increasing in research popularity due to its large surface area and flexibility for various individual modifications while demonstrating high resolution performance under imaging techniques. Activation methods greatly vary across nanoscale drug delivery molecules, but the most commonly used activation method uses specific wavelengths of light to release the cargo. Nanovalve-controlled cargo release uses low intensity light and plasmonic heating to release the cargo in a variation of MSN containing gold molecules. The two-photon activated photo-transducer (2-NPT) uses near IR wavelengths of light to induce breaking of a disulfide bond to release the cargo. Recently, nanodiamonds have demonstrated potential in drug delivery due to non-toxicity, spontaneous absorption through the skin, and ability to enter the blood-brain barrier.

Tissue engineering

Because cells are very sensitive to nanotopographical features, optimization of surfaces in tissue engineering has pushed the frontiers towards implantation. Under the appropriate conditions, a carefully crafted 3-dimensional scaffold is used to direct cell seeds towards artificial organ growth. The 3-D scaffold incorporates various nanoscale factors that control the environment for optimal and appropriate functionality. The scaffold is an analog of the in vivo extracellular matrix in vitro, allowing for successful artificial organ growth by providing the necessary, complex biological factors in vitro. Additional advantages include the possibility of cell expression manipulation, adhesion, and drug delivery.

Wounds

For abrasions and wounds, nanochemistry has demonstrated applications in improving the healing process. Electrospinning is a polymerization method used biologically in tissue engineering, but can be functionalized for wound dressing as well as drug delivery. This produces nanofibers which encourage cell proliferation, antibacterial properties, and controlled environment. These properties have been created in macroscale; however, nanoscale versions may show improved efficiency due to nanotopographical features. Targeted interfaces between nanofibers and wounds have higher surface area interactions and are advantageously in vivo.

There is evidence certain nanoparticles of silver are useful to inhibit some viruses and bacteria.

New developments in nanochemistry provide a variety of nanostructure materials with significant properties that are highly controllable. Some of the application of these nanostructure materials include SAMs and lithography, use of nanowires in sensors, and nanoenzymes.

Electrics

Nanowire compositions

Scientists have also devised a large number of nanowire compositions with controlled length, diameter, doping, and surface structure by using vapor and solution phase strategies. These oriented single crystals are being used in semiconductor nanowire devices such as diodes, transistors, logic circuits, lasers and sensors. Since nanowires have one dimensional structure meaning large surface to volume ratio, the diffusion resistance decreases. In addition, their efficiency in electron transport which is due to the quantum confinement effect, make their electrical properties be influenced by minor perturbation. Therefore, use of these nanowires in nanosensor elements increases the sensitivity in electrode response. As mentioned above, one dimensionality and chemical flexibility of the semiconductor nanowires make them applicable in nanolasers. Peidong Yang and his co-workers have done some research on room-temperature ultraviolet nanowire nanolasers in which the significant properties of these nanolasers have been mentioned. They have concluded that using short wavelength nanolasers have applications in different fields such as optical computing, information storage, and microanalysis.

Catalysis

Nanoenzymes (or Nanozymes)

Nanostructure materials mainly used in nanoparticle-based enzymes have drawn attraction due to the specific properties they show. Very small size of these nanoenzymes (or nanozymes) (1–100 nm) have provided them unique optical, magnetic, electronic, and catalytic properties. Moreover, the control of surface functionality of nano particles and predictable nanostructure of these small sized enzymes have made them to create a complex structure on their surface which in turn meet the needs of specific applications.

Research

Nanodiamonds

Synthesis

Fluorescent nanoparticles have broad applications, but their use into macroscopic arrays allows them to be used efficiently in applications of plasmonics, photonics and quantum communications that makes them highly sought after. While there are many methods in assembling nanoparticles array, especially gold nanoparticles, they tend to be weakly bonded to their substrate so it can't be used for wet chemistry processing steps or lithography. Nanodiamonds allow for a greater variability in access that can subsequently be used to couple plasmonic waveguides to realize quantum plasmonics circuitry.

Nanodiamonds can be synthesized by employing nanoscale carbonaceous seeds that are fabricated by a single step using a mask-free electron beam induced position technique to add amine groups to self-assemble nanodiamonds into arrays. The presence of dangling bonds at the nanodiamond surface allows them to be functionalized with a variety of ligands. The surfaces of these nanodiamonds are terminated with carboxylic acid groups, enabling their attachment to amine-terminated surfaces through carbodiimide coupling chemistry. This process gives a high yield do that this method relies on covalent bonding between the amine and carboxyl functional groups on amorphous carbon and nanodiamond surfaces in the presence of EDC. Thus unlike gold nanoparticle they can withstand processing and treatment, for many device applications.

Fluorescent (nitrogen vacancy)

Fluorescent properties in nanodiamonds arise from the presence of nitrogen vacancy (NV) centers, nitrogen atom next to a vacancy. Fluorescent nanodiamond (FND) was invented in 2005 and has since been used in various fields of study. The invention received a US patent in 2008 States7326837 B2 United States 7326837 B2, Chau-Chung Han; Huan-Cheng Chang & Shen-Chung Lee et al., "Clinical applications of crystalline diamond particles", issued Feb. 5, 2008, assigned to Academia Sinica, Taipei (TW), and a subsequent patent in 2012 States8168413 B2 United States 8168413 B2, Huan-Cheng Chang; Wunshian Fann & Chau-Chung Han, "Luminescent Diamond Particles", issued May 1, 2012, assigned to Academia Sinica, Taipei (TW). NV centres can be created by irradiating nanodiamond with high-energy particles (electrons, protons, helium ions), followed by vacuum-annealing at 600–800 °C. Irradiation forms vaccines in the diamond structure while vacuum-annealing migrates these vacancies, which will get trapped by nitrogen atoms within the nanodiamond. This process produces two types of NV centers. Two types of NV centers are formed—neutral (NV0) and negatively charged (NV–)—and these have different emission spectra. The NV– centre is of particular interest because it has an S = 1 spin ground state that can be spin-polarized by optical pumping and manipulated using electron paramagnetic resonance. Fluorescent nanodiamonds combine the advantages of semiconductor quantum dots (small size, high photostability, bright multicolor fluorescence) with biocompatibility, non-toxicity and rich surface chemistry, which means that they have the potential to revolutionize in vivo imaging application.

Drug-delivery and biological compatibility

Nanodiamonds have the ability to self-assemble and a wide range of small molecules, proteins antibodies, therapeutics and nucleic acids can bind to its surface allow for drug delivery, protein-mimicking and surgical implants. Other potential biomedical applications are the use of nanodiamonds as a support for solid-phase peptide synthesis and as sorbents for detoxification and separation and fluorescent nanodiamonds for biomedical imaging. Nanodiamonds are capable of biocompatibility, the ability to carry a broad range of therapeutics, dispersibility in water and scalability and thee potential for targeted therapy all properties needed for a drug delivery platform. The small size, stable core, rich surface chemistry, ability to self-assemble and low cytotoxicity of nanodiamonds have led to suggestions that they could be used to mimic globular proteins. Nanodiamonds have been mostly studied as potential injectable therapeutic agents for generalized drug delivery, but it has also been shown that films of Parylene nanodiamond composites can be used for localized sustained release of drugs over periods ranging from two days to one month.

Nanometer-size clusters

Monodispurse, nanometer-size clusters (also known as nanoclusters) are synthetically grown crystals whose size and structure influence their properties through the effects of quantum confinement. One method of growing these crystals is through inverse micellar cages in non aqueous solvents. Research conducted on the optical properties of MoS2 nanoclusters compared them to their bulk crystal counterparts and analyzed their absorbance spectra. The analysis reveals that size dependence of the absorbance spectrum by bulk crystals is continuous, whereas the absorbance spectrum of nanoclusters takes on discrete energy levels. This indicates a shift from solid-like to molecular-like behavior which occurs at a reported cluster size of 4.5 – 3.0 nm.

Interest in the magnetic properties of nanoclusters exists due to their potential use in magnetic recording, magnetic fluids, permanent magnets, and catalysis. Analysis of Fe clusters shows behavior consistent with ferromagnetic or superparamagnetic behavior due to strong magnetic interactions within clusters.

Dielectric properties of nanoclusters are also a subject interest due to their possible applications in catalysis, photocatalysis, microcapacitors, microelectronics, and nonlinear optics.

Notable researchers

There are several researchers in nanochemistry that have been credited with development of the field. Geoffrey A. Ozin, from the University of Toronto, is known as one of the "founding fathers of Nanochemistry" due to his four and a half decades of research on this subject. This research includes the study of Matrix isolation laser Raman spectroscopy, naked metal clusters chemistry and photochemistry, nanoporous materials, hybrid nanomaterials, mesoscopic materials, and ultrathin inorganic nanowires.

Another chemist who is also viewed as one of nanochemistry's pioneers is Charles M. Lieber at Harvard University. He is known for his contributions in the development of nano-scale technologies, particularly in the field of biology and medicine. The technologies include nanowires, a new class of quasi-one dimensional materials that have demonstrated superior electrical, optical, mechanical, and thermal properties and can be used potentially as biological sensors. Research under Lieber has delved into the use of nanowires for the purpose of mapping brain activity.

Shimon Weiss, a professor at the University of California, Los Angeles, is known for his research of fluorescent semiconductior nanocrystals, a subclass of quantum dots, for the purpose of biological labeling. Paul Alivisatos, from the University of California Berkeley, is also notable for his research on the fabrication and use of nanocrystals. This research has the potential to develop insight into the mechanisms of small scale particles such as the process of nucleation, cation exchange, and branching. A notable application of these crystals is the development of quantum dots.

Peidong Yang, another researcher from the University of California, Berkeley, is also notable for his contributions to the development of 1-dimensional nanostructures. Currently, the Yang group has active research projects in the areas of nanowire photonics, nanowire-based solar cells, nanowires for solar to fuel conversion, nanowire thermoelectrics, nanowire-cell interface, nanocrystal catalysis, nanotube nanofluidics, and plasmonics.

Hobbesian trap

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Hobbesian_trap 

The Hobbesian trap (or Schelling's dilemma) is a theory that explains why preemptive strikes occur between two groups, out of bilateral fear of an imminent attack. Without outside influences this situation will lead to a fear spiral (catch-22, vicious circle, Nash equilibrium) in which fear will lead to an arms race which in turn will lead to increasing fear. The Hobbesian trap can be explained in terms of game theory. Although cooperation would be the better outcome for both sides, mutual distrust leads to the adoption of strategies that have negative outcomes for individual players and all players combined. The theory has been used to explain outbreaks of conflicts and violence, spanning from individuals to states.

History

The theory is most commonly associated with Thomas Hobbes and Thomas Schelling.

Examples

Steven Pinker is a proponent of the theory of the Hobbesian trap and has applied the theory to many conflicts and outbreaks of violence between people, groups, tribes, societies and states. Issues of gun control have been described as a Hobbesian trap. A common example is the dilemma that both the armed burglar and the armed homeowner face when they meet each other. Neither side may want to shoot, but both are afraid of the other party shooting first so they may be inclined to fire pre-emptively, although the favorable outcome for both parties would be that nobody be shot.

A similar example between two states is the Cuban Missile Crisis. Fear and mutual distrust between the actors increased the likelihood of a preemptive strike. Hobbesian traps in nuclear weapons' case can be defused if both sides can threaten second strike, which is the capacity to retaliate with nuclear force after the first attack. This is the basis of Mutual assured destruction.

Avoidance

The Hobbesian trap can be avoided by influences that increase the trust between the two parties. In Hobbes' case, the hobbesian trap would be present in the state of nature where, in the absence of law and law enforcement, the credible threat of violence from others may justify pre-emptive attacks. For Hobbes, we avoid this problem by naming a ruler who pledges to punish violence with violence. In the Cuban Missile Crisis, for example, Kennedy and Khrushchev realized that they were caught in a Hobbesian trap which helped them to make concessions that reduced distrust and fear.

 

Urban horticulture

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Urban_horticulture 

Horticulture is the science and art of growing fruits and vegetables and also flowers or ornamental plants.

Urban horticulture specifically is the study of the relationship between plants and the urban environment. It focuses on the functional use of horticulture so as to maintain and improve the surrounding urban area. With the expansion of cities and rapid urbanization, this field of study is large and complex and its study has only recently gained momentum. It has an undeniable relationship to production horticulture in that fruits, vegetables and other plants are grown for harvest, aesthetic, architectural, recreational and psychological purposes, but it extends far beyond these benefits. The value of plants in the urban environment has yet to be thoroughly researched or quantified.

Salad lettuce cultivation at the Growing Communities' urban plot, in Springfield Park, Clapton, North London.

 

Small radish grown on a balcony in Barcelona city

 

A variety of flowers and vegetables grown under metal halide lamps

History

Horticulture and the integration of nature into our civilization has been a major part in the establishment of our cities. When nomadic civilizations began settling down, their major trading centers were the market gardens and farms. Urban horticulture rapidly progressed with the birth of cities and the increase in experimentation and exchange of ideas. These insights led to the field being dispersed to farmers in the hinterlands. For centuries, the built environment such as homes, public buildings, etc. were integrated with cultivation in the form of gardens, farms, and grazing lands, Kitchen gardens, farms, common grazing land, etc. Therefore, horticulture was a regular part of everyday life in the city. With the Industrial Revolution and the related increasing populations rapidly changed the landscape and replaced green spaces with brick and asphalt. After the nineteenth century, Horticulture was then selectively restored in some urban spaces as a response to the unhealthy conditions of factory neighborhoods and cities began seeing the development of parks.

Post World War II trends

Early urban horticulture movements majorly served the purposes of short term welfare during recession periods, philanthropic charity to uplift "the masses" or patriotic relief. The tradition of urban horticulture mostly declined after World War II as suburbs became the focus of residential and commercial growth. Most of the economically stable population moved out of the cities into the suburbs, leaving only slums and ghettos at the city centers. However, there were a few exceptions of garden projects initiated by public housing authorities in the 1950s and 1960s for the purpose of beautification and tenant pride. But for the most part as businesses also left the metropolitan areas, it generated wastelands and areas of segregated poverty.

Inevitably the disinvestment of major city centers, specifically in America resulted in the drastic increase of vacant lots. Existing buildings became uninhabitable, houses were abandoned and even productive industrial land became vacant. Modern community gardening, urban agriculture, and food security movements were a form of response to battle the above problems at a local level. In fact other movements at that time such as the peace, environmental, women's, civil rights, and "back-to-the-city" movements of the 1960s and 1970s and the environmental justice movement of the 1980s and 1990s saw opportunity in these vacant lands as a way of reviving communities through school and community gardens, farmers' markets, and urban agriculture.

Modern community garden movement

Things have taken a turn in the twenty-first century as people are recognizing the need for local community gardens and green spaces. It is not the concept but the purposes that are new. The main goals of this movement include cleaning up neighborhoods, pushing out drug dealing that occurs at empty lots, growing and preserving food for consumption, restoring nature to industrial areas, and bringing the farming traditions to urban cities. Essentially community gardening is seen as way of creating a relationship between people and a place through social and physical engagement. Most urban gardens are created on vacant land that vary in size and are generally gardened as individual plots by community members. Such areas can support social, cultural, and artistic events and contribute to the rebuilding of local community spirit. The modern community garden movement is initiated by neighborhoods along with the support of the governments and non-profit organizations. Some gardens are linked to public housing projects, schools through garden-based learning programs, churches and social agencies and some even employ those who are incarcerated. Community gardens which are now a large part of the urban horticulture movement are different from the earlier periods of grand park development in that the latter only served to free the people from the industrialism. In addition a community garden is more beneficial and engaging than a mere lawn or park and serves as a valuable access to nature where wilderness is unavailable. This movement helped create and sustain relationships between city dwellers and the soil and contributed to a different kind of urban environmentalism that did not have any characteristics of reform charity.

Despite that it has been 30 years since the first community gardens in the US, there is no concrete analysis of current urban gardens and their organizations. The American Community Gardening Association (ACGA) has estimations that show that municipal governments and non-profit organizations operate gardening programs in about 250 cities and towns, although the staff of this organization admits that this number could in reality be twice as large. In 1994 survey, the National Gardening Association found that 6.7 million households, that weren't involved in gardening would be interested in doing so if there was a plot nearby. A more recent survey showed that more gardens are being created in cities as opposed to being lost to economic development.

Today urban horticulture has several components that include more than just community gardens, such as market gardens, small farms and farmers' markets and is an important aspect of community development. Another result of urban horticulture is the food security movement where locally grown food is given precedence through several projects and programs, thus providing low-cost and nutritious food. Urban community gardens and the food security movement was a response to the problems of industrial agriculture and to solve its related problems of price inflation, lack of supermarkets, food scarcity, etc.

Benefits

Horticulture by itself is a practical and applied science, which means it can have a significance in our everyday lives. As community gardens cannot actually compete with market-based land uses, it is essential to find other ways to understand their various benefits such as their contribution to social, human, and financial well-being. Frederick Law Olmsted, the designer of New York City's Central Park observed that the trees, meadows, ponds and wildlife tranquilize the stresses of city life. According to various studies over the years, nature has a very positive impact over human health and even more so in an emotional and psychological sense. Trees, grass, and flower gardens, due to their presence as well as visibility, increase people's life satisfaction by reducing fatigue and irritation and restoring a sense of calm. In fact Honeyman tested the restorative value of nature scenes in urban settings and discovered that vegetation in an urban setting produced more mental restoration as opposed to areas without vegetation. In addition, areas with only nature did not have as much of a positive psychological impact as did the combination of urban areas and nature.

One of the obvious health benefits of gardening is the increased intake of fruits and vegetables. But the act of gardening itself, is also a major health benefit. Gardening is a low-impact exercise, which when added into daily activities, can help reduce weight, lower stress, and improve overall health. A recent study showed a reduced body mass index and lower weight in community gardeners compared with their non-gardening counterparts  The study showed men who gardened had a body mass index 2.36 lower and were 62% less likely to be overweight than their neighbors, while women were 46% less likely to be overweight with a body mass index 1.88 lower than their neighbors. Access to urban gardens can improve health through nutritious, edible plantings, as well by getting people outside and promoting more activity in their environments.

Gardening programs in inner-city schools have become increasingly popular as a way to teach children not only about healthy eating habits, but also to encourage students to become active learners. Besides getting students outside and moving, and encouraging an active lifestyle, children also learn leadership, teamwork, communication and collaboration skills, in addition to critical and creative thinking skills. Gardening in schools will enable children to share with their families the health and nutrition benefits of eating fresh fruits and vegetables. Because weather and soil conditions are in a state of constant change, students learn to adapt their thinking and creatively problem solve, depending on the situations that arise. Students also learn to interact and communicate with a diverse population of people, from other students to adult volunteers. These programs benefit students' health and enable them to be active contributors in the world around them.

Gardens and other green spaces also increase social activity and help in creating a sense of place, apart from their various other purposes such as enhancing the community by mediating environmental factors. There is also a huge disparity in the availability of sources that provide nutritious and affordable foods especially around urban centers which have problems of poverty, lack of public transport and abandonment by supermarkets. Therefore, inner city community gardens can be a valuable source of nutrition at an affordable cost in the most easily accessible way.

In order to understand and thereby maximize the benefits of urban horticulture, it is essential to document the effects of horticulture activities and quantify the benefits so that governments and private industries can make the appropriate changes. Horticulturists have always been involved in the botanical and physical aspects of horticulture but an involvement in its social and emotional factors would be highly beneficial to communities, cities and to the field of horticulture and its profession. Based on this, in the 1970s, the International Society for Horticultural Science recognized this need for research on the functional use of plants in an urban setting along with the need of improved communication between scientists in this field of research and people who utilize plants. The Commission for Urban Horticulture was established in 1982 which deals with plants grown in urban areas, management techniques, the functional use of these plants as well the shortcomings of the current lack of knowledge regarding this field. The establishment of such a commission is an important indicator that this topic has reached a level of international recognition.

Economic benefits

There are many different economic benefits from gardening from saving money purchasing food and even on the utility bills. Developing countries can spend up to 60–80 percent of income on buying food alone. In Barbara Lake, Milfront Taciano and Gavin Michaels Journal of Psychology title "The Relative Influence of Psycho-Social Factors on Urban Gardening", they say that while people are saving money on buying food, having roof top gardens are also becoming popular. Having green roofs can reduce the cost of heating in the winter and help stay cool in the summer. Green roofs also can lower the cost of roof replacement. While green roofs are an addition to urban horticulture people are eating healthy while also improving the value of their property. Other benefits include increased employment from non-commercial jobs where producers include reductions on the cost of food (Lake, Taciano, and Michael).

Production practices

Tomato plants growing in a pot farming alongside a small house in New Jersey in fifteen garbage cans filled with soil, grew over 700 tomatoes during the summer of 2013.

Crops are grown in flowerpots, growbags, small gardens or larger fields, using traditional or high-tech and innovative practices. Some new techniques that have been adapted to the urban situation and tackle the main city restrictions are also documented. These include horticultural production on built-up land using various types of substrates (e.g. roof top, organic production and hydroponic/aeroponic production). Because of this, it is also known as roof-top vegetable gardening/horticulture and container vegetable gardening/horticulture.

Urban and peri-urban horticulture in Africa

A report of the United Nations Food and Agriculture Organization, Growing greener cities in Africa, states that market gardening – i.e. irrigated, commercial production of fruit and vegetables in areas designated for the purpose, or in other urban open spaces – is the single most important source of locally grown, fresh produce in 10 out of 27 African countries for which data are available. Market gardening produces most of all the leafy vegetables consumed in Accra, Dakar, Bangui, Brazzaville, Ibadan, Kinshasa and Yaoundé, cities that, between them, have a total population of 22.5 million. Market gardens provide around half of the leafy vegetable supply in Addis Ababa, Bissau and Libreville. The report says that in most of urban Africa, market gardening is an informal and often illegal activity, which has grown with little official recognition, regulation or support. Most gardeners have no formal title to their land, and many lose it overnight. Land suitable for horticulture is being taken for housing, industry and infrastructure. To maximize earnings from insecure livelihoods, many gardeners are overusing pesticide and urban waste water.

Vertical farming

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Vertical_farming 

 

Lettuce grown in indoor vertical farming system

Vertical farming is the practice of growing crops in vertically stacked layers. It often incorporates controlled-environment agriculture, which aims to optimize plant growth, and soilless farming techniques such as hydroponics, aquaponics, and aeroponics. Some common choices of structures to house vertical farming systems include buildings, shipping containers, tunnels, and abandoned mine shafts. As of 2020, there is the equivalent of about 30 ha (74 acres) of operational vertical farmland in the world. The modern concept of vertical farming was proposed in 1999 by Dickson Despommier, professor of Public and Environmental Health at Columbia University. Despommier and his students came up with a design of a skyscraper farm that could feed 50,000 people. Although the design has not yet been built, it successfully popularized the idea of vertical farming. Current applications of vertical farmings coupled with other state-of-the-art technologies, such as specialized LED lights, have resulted in over 10 times the crop yield than would receive through traditional farming methods.

The main advantage of utilizing vertical farming technologies is the increased crop yield that comes with a smaller unit area of land requirement. The increased ability to cultivate a larger variety of crops at once because crops do not share the same plots of land while growing is another sought-after advantage. Additionally, crops are resistant to weather disruptions because of their placement indoors, meaning less crops lost to extreme or unexpected weather occurrences. Because of its limited land usage, vertical farming is less disruptive to the native plants and animals, leading to further conservation of the local flora and fauna.

Vertical farming technologies face economic challenges with large start-up costs compared to traditional farms. In Victoria, Australia, a “hypothetical 10 level vertical farm” would cost over 850 times more per cubic meter of arable land than a traditional farm in rural Victoria. Vertical farms also face large energy demands due to the use of supplementary light like LEDs. Moreover, if non-renewable energy is used to meet these energy demands, vertical farms could produce more pollution than traditional farms or greenhouses.

Techniques of vertical farming

Indoor Hydroponics of Morus, Japan

Hydroponics

Hydroponics refers to the technique of growing plants without soil. In hydroponic systems, the roots of plants are submerged in liquid solutions containing macronutrients, such as nitrogen, phosphorus, sulphur, potassium, calcium, and magnesium, as well as trace elements, including iron, chlorine, manganese, boron, zinc, copper, and molybdenum. Additionally, inert (chemically inactive) mediums such as gravel, sand, and sawdust are used as soil substitutes to provide support for the roots.

The advantages of hydroponics include the ability to increase yield per area and reduce water usage. A study has shown that, compared to conventional farming, hydroponic farming could increase the yield per area of lettuce by around 11 times while requiring 13 times less water. Due to these advantages, hydroponics is the predominant growing system used in vertical farming.

Aquaponics with catfish

Aquaponics

The term aquaponics is coined by combining two words: aquaculture, which refers to fish farming, and hydroponics—the technique of growing plants without soil. Aquaponics takes hydroponics one step further by integrating the production of terrestrial plants with the production of aquatic organisms in a closed-loop system that mimics nature itself. Nutrient-rich wastewater from the fish tanks is filtered by a solid removal unit and then led to a bio-filter, where toxic ammonia is converted to nutritious nitrate. While absorbing nutrients, the plants then purify the wastewater, which is recycled back to the fish tanks. Moreover, the plants consume carbon dioxide produced by the fish, and water in the fish tanks obtains heat and helps the greenhouse maintain temperature at night to save energy. As most commercial vertical farming systems focus on producing a few fast-growing vegetable crops, aquaponics, which also includes an aquacultural component, is currently not as widely used as conventional hydroponics.

Aeroponics

Aeroponically-grown chives

The invention of aeroponics was motivated by the initiative of NASA (the National Aeronautical and Space Administration) to find an efficient way to grow plants in space in the 1990s. Unlike conventional hydroponics and aquaponics, aeroponics does not require any liquid or solid medium to grow plants in. Instead, a liquid solution with nutrients is misted in air chambers where the plants are suspended. By far, aeroponics is the most sustainable soil-less growing technique, as it uses up to 90% less water than the most efficient conventional hydroponic systems and requires no replacement of growing medium. Moreover, the absence of growing medium allows aeroponic systems to adopt a vertical design, which further saves energy as gravity automatically drains away excess liquid, whereas conventional horizontal hydroponic systems often require water pumps for controlling excess solution. Currently, aeroponic systems have not been widely applied to vertical farming, but are starting to attract significant attention.

Controlled-environment agriculture

Controlled-environment agriculture (CEA) is the modification of the natural environment to increase crop yield or extend the growing season. CEA systems are typically hosted in enclosed structures such as greenhouses or buildings, where control can be imposed on environmental factors including air, temperature, light, water, humidity, carbon dioxide, and plant nutrition. In vertical farming systems, CEA is often used in conjunction with soilless farming techniques such as hydroponics, aquaponics, and aeroponics.

Types of vertical farming

Building-based vertical farms

Vertical farm in Moscow.

Abandoned buildings are often reused for vertical farming, such as a farm at Chicago called “The Plant,” which was transformed from an old meatpacking plant. However, new builds are sometimes also constructed to house vertical farming systems.

Shipping-container vertical farms

Recycled shipping containers are an increasingly popular option for housing vertical farming systems. The shipping containers serve as standardized, modular chambers for growing a variety of plants, and are often equipped with LED lighting, vertically stacked hydroponics, smart climate controls, and monitoring sensors. Moreover, by stacking the shipping containers, farms can save space even further and achieve higher yield per square foot.

Deep farms

A “deep farm” is a vertical farm built from refurbished underground tunnels or abandoned mine shafts. As temperature and humidity underground are generally temperate and constant, deep farms require less energy for heating. Deep farms can also use nearby groundwater to reduce the cost of water supply. Despite low costs, a deep farm can produce 7 to 9 times more food than a conventional farm above ground on the same area of land, according to Saffa Riffat, chair in Sustainable Energy at the University of Nottingham. Coupled with automated harvesting systems, these underground farms can be fully self-sufficient.

History

Initial propositions

Dickson Despommier, professor of Public and Environmental Health at Columbia University, founded the root of the concept of vertical farming. In 1999, he challenged his class of graduate students to calculate how much food they could grow on the rooftops of New York. The student concluded that they could only feed about 1000 people. Unsatisfied with the results, Despommier suggested growing plants indoors instead, on multiple layers vertically. Despommier and his students then proposed a design of a 30-story vertical farm equipped with artificial lighting, advanced hydroponics, and aeroponics that could produce enough food for 50,000 people. They further outlined that approximately 100 kinds of fruits and vegetables would grow on the upper floors while lower floors would house chickens and fish subsisting on the plant waste. Although Despommier's skyscraper farm has not yet been built, it popularized the idea of vertical farming and inspired many later designs.

Implementations

Developers and local governments in multiple cities have expressed interest in establishing a vertical farm: Incheon (South Korea), Abu Dhabi (United Arab Emirates), Dongtan (China), New York City, Portland, Los Angeles, Las Vegas, Seattle, Surrey, Toronto, Paris, Bangalore, Dubai, Shanghai, and Beijing. Around US$ 1.8 billion were invested into startups operating in the sector between 2014 and November 2020.

In 2009, the world's first pilot production system was installed at Paignton Zoo Environmental Park in the United Kingdom. The project showcased vertical farming and provided a solid base to research sustainable urban food production. The produce is used to feed the zoo's animals while the project enables evaluation of the systems and provides an educational resource to advocate for change in unsustainable land-use practices that impact upon global biodiversity and ecosystem services.

In 2010 the Green Zionist Alliance proposed a resolution at the 36th World Zionist Congress calling on Keren Kayemet L'Yisrael (Jewish National Fund in Israel) to develop vertical farms in Israel. Moreover, a company named "Podponics" built a vertical farm in Atlanta consisting of over 100 stacked "growpods" in 2010 but reportedly went bankrupt in May 2016.

In 2012 the world's first commercial vertical farm was opened in Singapore, developed by Sky Greens Farms, and is three stories high. They currently have over 100 nine meter-tall towers.

In 2012, a company named The Plant debuted its newly developed vertical farming system housed in an abandoned meatpacking building in Chicago, Illinois. The utilization of abandoned buildings to house vertical farms and other sustainable farming methods are a fact of the rapid urbanization of modern communities.

In 2013 the Association for Vertical Farming (AVF) was founded in Munich (Germany). By May 2015, the AVF had expanded with regional chapters all over Europe, Asia, USA, Canada and the United Kingdom. This organization unites growers and inventors to improve food security and sustainable development. The AVF focuses on advancing vertical farming technologies, designs and businesses by hosting international info-days, workshops, and summits.

In 2015 the London company, Growing Underground, began the production of leafy green produce underground in abandoned underground World War II tunnels.

In 2016, a startup called Local Roots launched the "TerraFarm", a vertical farming systems hosted in a 40-foot shipping container, which includes computer vision integrated with an artificial neural network to monitor the plants; and is remotely monitored from California. It is claimed that the TerraFarm system "has achieved cost parity with traditional, outdoor farming" with each unit producing the equivalent of "three to five acres of farmland," using 97% less water through water recapture and harvesting the evaporated water through the air conditioning. The first vertical farm in a US grocery store opened in Dallas, Texas in 2016, now closed.

In 2017, a Japanese company, Mirai, began marketing its multi-level vertical farming system. The company states that it can produce 10,000 heads of lettuce a day - 100 times the amount that could be produced with traditional agricultural methods, because their special purpose LED lights can decrease growing times by a factor of 2.5. Additionally, this can all be achieved with 40% less energy usage, 80% less food waste, and 99% less water usage than in traditional farming methods. Further requests have been made to implement this technology in several other Asian countries.

In 2019, Kroger partnered with German startup Infarm to install modular vertical farms in two Seattle-area grocery stores.

Advantages

Efficiency

Traditional farming's arable land requirements are too large and invasive to remain sustainable for future generations. With the ever-so-rapid population growth rates, it is expected that arable land per person will drop about 66% in 2050 in comparison to 1970. Vertical farming allows for, in some cases, over ten times the crop yield per acre than traditional methods. Unlike traditional farming in non-tropical areas, indoor farming can produce crops year-round. All-season farming multiplies the productivity of the farmed surface by a factor of 4 to 6 depending on the crop. With crops such as strawberries, the factor may be as high as 30.

Vertical farming also allows for the production of a larger variety of harvestable crops because of its usage of isolated crop sectors. As opposed to a traditional farm where one type of crop is harvested per season, vertical farms allow for a multitude of different crops to be grown and harvested at once due to their individual land plots.

According to the USDA, vertical farm produce only travels a short distance to reach stores compared to traditional farming method produce.

The United States Department of Agriculture predicts the worldwide population to exceed 9 billion by 2050, most of which will be living in urban or city areas. Vertical farming is the USDA's predicted answer to the potential food shortage as population increases. This method of farming is environmentally responsible by lowering emission and reducing needed water. This type of urban farming that would allow for nearly immediate farm to store transport would reduce distribution.

In a workshop on vertical farming put on by the USDA and the Department of Energy experts in vertical farming discussed plant breeding, pest management, and engineering. Control of pests (like insects, birds and rodents) is easily managed in vertical farms, because the area is so well-controlled. Without the need of chemical pesticides the ability to grow organic crops is easier than in traditional farming.

Resistance to weather

Crops grown in traditional outdoor farming depend on supportive weather and suffer from undesirable temperatures, rain, monsoon, hailstorm, tornado, flooding, wildfires, and drought. "Three recent floods (in 1993, 2007 and 2008) cost the United States billions of dollars in lost crops, with even more devastating losses in topsoil. Changes in rain patterns and temperature could diminish India's agricultural output by 30 percent by the end of the century."

The issue of adverse weather conditions is especially relevant for arctic and sub-arctic areas like Alaska and northern Canada where traditional farming is largely impossible. Food insecurity has been a long-standing problem in remote northern communities where fresh produce has to be shipped large distances resulting in high costs and poor nutrition. Container-based farms can provide fresh produce year-round at a lower cost than shipping in supplies from more southerly locations with a number of farms operating in locations such as Churchill, Manitoba, and Unalaska, Alaska. As with disruption to crop growing, local container-based farms are also less susceptible to disruption than the long supply chains necessary to deliver traditionally grown produce to remote communities. Food prices in Churchill spiked substantially after floods in May and June 2017 forced the closure of the rail line that forms the only permanent overland connection between Churchill and the rest of Canada.

Environmental conservation

Up to 20 units of outdoor farmland per unit of vertical farming could return to its natural state, due to vertical farming's increased productivity. Vertical farming would reduce the amount of farmland, thus saving many natural resources.

Deforestation and desertification caused by agricultural encroachment on natural biomes could be avoided. Producing food indoors reduces or eliminates conventional plowing, planting, and harvesting by farm machinery, protecting soil, and reducing emissions.

Traditional farming is often invasive to the native flora and fauna because it requires such a large area of arable land. One study showed that wood mouse populations dropped from 25 per hectare to 5 per hectare after harvest, estimating 10 animals killed per hectare each year with conventional farming. In comparison, vertical farming would cause nominal harm to wildlife because of its limited space usage.

Problems

Economics

Vertical farms must overcome the financial challenge of large startup costs. The initial building costs could exceed $100 million for a 60 hectare vertical farm. Urban occupancy costs can be high, resulting in much higher startup costs – and a longer break even time – than for a traditional farm in rural areas.

Opponents question the potential profitability of vertical farming. In order for vertical farms to be successful financially, high value crops must be grown since traditional farms provide low value crops like wheat at cheaper costs than a vertical farm. Louis Albright, a professor in biological and environmental engineering at Cornell stated that a loaf of bread that was made from wheat grown in a vertical farm would cost US$27. However, according to the US Bureau of Labor Statistics, the average loaf of bread cost US$1.296 in September 2019, clearly showing how crops grown in vertical farms will be noncompetitive compared to crops grown in traditional outdoor farms. In order for vertical farms to be profitable, the costs of operating these farms must decrease. The developers of the TerraFarm system produced from second hand, 40 foot shipping containers claimed that their system "has achieved cost parity with traditional, outdoor farming".

A theoretical 10 storey vertical wheat farm could produce up to 1,940 tons of wheat per hectare compared to a global average of 3.2 tons of wheat per hectare (600 times yield). Current methods require enormous energy consumption for lighting, temprerature, humidity control, carbon dioxide input and fertilizer and consequently the authors concluded it was "unlikely to be economically competitive with current market prices".

According to a report in The Financial Times as of 2020, most vertical farming companies have been unprofitable, except for a number of Japanese companies.

Energy use

During the growing season, the sun shines on a vertical surface at an extreme angle such that much less light is available to crops than when they are planted on flat land. Therefore, supplemental light would be required. Bruce Bugbee claimed that the power demands of vertical farming would be uncompetitive with traditional farms using only natural light. Environmental writer George Monbiot calculated that the cost of providing enough supplementary light to grow the grain for a single loaf would be about $15. An article in the Economist argued that "even though crops growing in a glass skyscraper will get some natural sunlight during the day, it won't be enough" and "the cost of powering artificial lights will make indoor farming prohibitively expensive". Moreover, researchers determined that if only solar panels were to be used to meet the energy consumption of a vertical farm, “the area of solar panels required would need to be a factor of twenty times greater than the arable area on a multi-level indoor farm”, which will be hard to accomplish with larger vertical farms. A hydroponic farm growing lettuce in Arizona would require 15,000 kJ of energy per kilogram of lettuce produced. To put this amount of energy into perspective, a traditional outdoor lettuce farm in Arizona only requires 1100 kJ of energy per kilogram of lettuce grown.

As the book by Dr. Dickson Despommier "The Vertical Farm" proposes a controlled environment, heating and cooling costs will resemble those of any other multiple story building. Plumbing and elevator systems are necessary to distribute nutrients and water. In the northern continental United States, fossil fuel heating cost can be over $200,000 per hectare. Research conducted in 2015 compared the growth of lettuce in Arizona using conventional agricultural methods and a hydroponic farm. They determined that heating and cooling made up more than 80% of the energy consumption in the hydroponic farm, with the heating and cooling needing 7400 kJ per kilogram of lettuce produced. According to the same study, the total energy consumption of the hydroponic farm is 90,000 kJ per kilogram of lettuce. If the energy consumption is not addressed, vertical farms may be an unsustainable alternative to traditional agriculture.

Pollution

There are a number of interrelated challenges with some potential solutions:

• Power needs: If power needs are met by fossil fuels, the environmental effect may be a net loss; even building low-carbon capacity to power the farms may not make as much sense as simply leaving traditional farms in place, while burning less coal. Louis Albright argued that in a “closed-system urban farming based on electrically generated photosynthetic light”, a pound of lettuce would result in 8 pounds of carbon dioxide being produced at a power plant, and 4,000 pounds of lettuce produced would be equivalent to the annual emissions of a family car. He also argues that the carbon footprint of tomatoes grown in a similar system would be twice as big as the carbon footprint of lettuce. However, lettuce produced in a greenhouse that allows for sunlight to reach the crops saw a 300 percent reduction in carbon dioxide emissions per head of lettuce. As vertical farm system become more efficient in harnessing sunlight, they will produce less pollution.

• Carbon emission: A vertical farm requires a CO₂ source, most likely from combustion if colocated with electric utility plants; absorbing CO₂ that would otherwise be jettisoned is possible. Greenhouses commonly supplement carbon dioxide levels to 3–4 times the atmospheric rate. This increase in CO₂ increases photosynthesis at varying rates, averaging 50%, contributing not only to higher yields, but also to faster plant maturation, shrinking of pores and greater resilience to water stress (both too much and little). Vertical farms need not exist in isolation, hardier mature plants could be transferred to traditional greenhouse, freeing up space and increasing cost flexibility.

• Crop damage: Some greenhouses burn fossil fuels purely to produce CO₂, such as from furnaces, which contain pollutants such as sulphur dioxide and ethylene. These pollutants can significantly damage plants, so gas filtration is a component of high production systems.

• Ventilation: "Necessary" ventilation may allow CO₂ to leak into the atmosphere, though recycling systems could be devised. This is not limited to humidity tolerant and humidity intolerant crop polyculture cycling (as opposed to monoculture).

• Light Pollution: Greenhouse growers commonly exploit photoperiodism in plants to control whether the plants are in a vegetative or reproductive stage. As part of this control, the lights stay on past sunset and before sunrise or periodically throughout the night. Single story greenhouses have attracted criticism over light pollution, though a typical urban vertical farm may also produce light pollution.

• Water Pollution: Hydroponic greenhouses regularly change the water, producing water containing fertilizers and pesticides that must be disposed of. Spreading the effluent over neighboring farmland or wetlands would be difficult for an urban vertical farm, while water treatment remedies (natural or otherwise) could be part of a solution.

 

Molecular nanotechnology

From Wikipedia, the free encyclopedia

 

 

Kinesin is a protein complex functioning as a molecular biological machine. It uses protein domain dynamics on nanoscales

Molecular nanotechnology (MNT) is a technology based on the ability to build structures to complex, atomic specifications by means of mechanosynthesis. This is distinct from nanoscale materials. Based on Richard Feynman's vision of miniature factories using nanomachines to build complex products (including additional nanomachines), this advanced form of nanotechnology (or molecular manufacturing) would make use of positionally-controlled mechanosynthesis guided by molecular machine systems. MNT would involve combining physical principles demonstrated by biophysics, chemistry, other nanotechnologies, and the molecular machinery of life with the systems engineering principles found in modern macroscale factories.

A ribosome is a biological machine.

Introduction

While conventional chemistry uses inexact processes obtaining inexact results, and biology exploits inexact processes to obtain definitive results, molecular nanotechnology would employ original definitive processes to obtain definitive results. The desire in molecular nanotechnology would be to balance molecular reactions in positionally-controlled locations and orientations to obtain desired chemical reactions, and then to build systems by further assembling the products of these reactions.

A roadmap for the development of MNT is an objective of a broadly based technology project led by Battelle (the manager of several U.S. National Laboratories) and the Foresight Institute. The roadmap was originally scheduled for completion by late 2006, but was released in January 2008. The Nanofactory Collaboration is a more focused ongoing effort involving 23 researchers from 10 organizations and 4 countries that is developing a practical research agenda specifically aimed at positionally-controlled diamond mechanosynthesis and diamondoid nanofactory development. In August 2005, a task force consisting of 50+ international experts from various fields was organized by the Center for Responsible Nanotechnology to study the societal implications of molecular nanotechnology.

Projected applications and capabilities

Smart materials and nanosensors

One proposed application of MNT is so-called smart materials. This term refers to any sort of material designed and engineered at the nanometer scale for a specific task. It encompasses a wide variety of possible commercial applications. One example would be materials designed to respond differently to various molecules; such a capability could lead, for example, to artificial drugs which would recognize and render inert specific viruses. Another is the idea of self-healing structures, which would repair small tears in a surface naturally in the same way as self-sealing tires or human skin.

A MNT nanosensor would resemble a smart material, involving a small component within a larger machine that would react to its environment and change in some fundamental, intentional way. A very simple example: a photosensor might passively measure the incident light and discharge its absorbed energy as electricity when the light passes above or below a specified threshold, sending a signal to a larger machine. Such a sensor would supposedly cost less and use less power than a conventional sensor, and yet function usefully in all the same applications — for example, turning on parking lot lights when it gets dark.

While smart materials and nanosensors both exemplify useful applications of MNT, they pale in comparison with the complexity of the technology most popularly associated with the term: the replicating nanorobot.

Replicating nanorobots

MNT nanofacturing is popularly linked with the idea of swarms of coordinated nanoscale robots working together, a popularization of an early proposal by K. Eric Drexler in his 1986 discussions of MNT, but superseded in 1992. In this early proposal, sufficiently capable nanorobots would construct more nanorobots in an artificial environment containing special molecular building blocks.

Critics have doubted both the feasibility of self-replicating nanorobots and the feasibility of control if self-replicating nanorobots could be achieved: they cite the possibility of mutations removing any control and favoring reproduction of mutant pathogenic variations. Advocates address the first doubt by pointing out that the first macroscale autonomous machine replicator, made of Lego blocks, was built and operated experimentally in 2002. While there are sensory advantages present at the macroscale compared to the limited sensorium available at the nanoscale, proposals for positionally controlled nanoscale mechanosynthetic fabrication systems employ dead reckoning of tooltips combined with reliable reaction sequence design to ensure reliable results, hence a limited sensorium is no handicap; similar considerations apply to the positional assembly of small nanoparts. Advocates address the second doubt by arguing that bacteria are (of necessity) evolved to evolve, while nanorobot mutation could be actively prevented by common error-correcting techniques. Similar ideas are advocated in the Foresight Guidelines on Molecular Nanotechnology, and a map of the 137-dimensional replicator design space recently published by Freitas and Merkle provides numerous proposed methods by which replicators could, in principle, be safely controlled by good design.

However, the concept of suppressing mutation raises the question: How can design evolution occur at the nanoscale without a process of random mutation and deterministic selection? Critics argue that MNT advocates have not provided a substitute for such a process of evolution in this nanoscale arena where conventional sensory-based selection processes are lacking. The limits of the sensorium available at the nanoscale could make it difficult or impossible to winnow successes from failures. Advocates argue that design evolution should occur deterministically and strictly under human control, using the conventional engineering paradigm of modeling, design, prototyping, testing, analysis, and redesign.

In any event, since 1992 technical proposals for MNT do not include self-replicating nanorobots, and recent ethical guidelines put forth by MNT advocates prohibit unconstrained self-replication.

Medical nanorobots

One of the most important applications of MNT would be medical nanorobotics or nanomedicine, an area pioneered by Robert Freitas in numerous books and papers. The ability to design, build, and deploy large numbers of medical nanorobots would, at a minimum, make possible the rapid elimination of disease and the reliable and relatively painless recovery from physical trauma. Medical nanorobots might also make possible the convenient correction of genetic defects, and help to ensure a greatly expanded lifespan. More controversially, medical nanorobots might be used to augment natural human capabilities. One study has reported on how conditions like tumors, arteriosclerosis, blood clots leading to stroke, accumulation of scar tissue and localized pockets of infection can possibly be addressed by employing medical nanorobots.

Utility fog

Diagram of a 100 micrometer foglet

Another proposed application of molecular nanotechnology is "utility fog" — in which a cloud of networked microscopic robots (simpler than assemblers) would change its shape and properties to form macroscopic objects and tools in accordance with software commands. Rather than modify the current practices of consuming material goods in different forms, utility fog would simply replace many physical objects.

Phased-array optics

Yet another proposed application of MNT would be phased-array optics (PAO). However, this appears to be a problem addressable by ordinary nanoscale technology. PAO would use the principle of phased-array millimeter technology but at optical wavelengths. This would permit the duplication of any sort of optical effect but virtually. Users could request holograms, sunrises and sunsets, or floating lasers as the mood strikes. PAO systems were described in BC Crandall's Nanotechnology: Molecular Speculations on Global Abundance in the Brian Wowk article "Phased-Array Optics."

Potential social impacts

Molecular manufacturing is a potential future subfield of nanotechnology that would make it possible to build complex structures at atomic precision. Molecular manufacturing requires significant advances in nanotechnology, but once achieved could produce highly advanced products at low costs and in large quantities in nanofactories weighing a kilogram or more. When nanofactories gain the ability to produce other nanofactories production may only be limited by relatively abundant factors such as input materials, energy and software.

The products of molecular manufacturing could range from cheaper, mass-produced versions of known high-tech products to novel products with added capabilities in many areas of application. Some applications that have been suggested are advanced smart materials, nanosensors, medical nanorobots and space travel. Additionally, molecular manufacturing could be used to cheaply produce highly advanced, durable weapons, which is an area of special concern regarding the impact of nanotechnology. Being equipped with compact computers and motors these could be increasingly autonomous and have a large range of capabilities.

According to Chris Phoenix and Mike Treder from the Center for Responsible Nanotechnology as well as Anders Sandberg from the Future of Humanity Institute molecular manufacturing is the application of nanotechnology that poses the most significant global catastrophic risk. Several nanotechnology researchers state that the bulk of risk from nanotechnology comes from the potential to lead to war, arms races and destructive global government. Several reasons have been suggested why the availability of nanotech weaponry may with significant likelihood lead to unstable arms races (compared to e.g. nuclear arms races): (1) A large number of players may be tempted to enter the race since the threshold for doing so is low; (2) the ability to make weapons with molecular manufacturing will be cheap and easy to hide; (3) therefore lack of insight into the other parties' capabilities can tempt players to arm out of caution or to launch preemptive strikes; (4) molecular manufacturing may reduce dependency on international trade, a potential peace-promoting factor; (5) wars of aggression may pose a smaller economic threat to the aggressor since manufacturing is cheap and humans may not be needed on the battlefield.

Since self-regulation by all state and non-state actors seems hard to achieve, measures to mitigate war-related risks have mainly been proposed in the area of international cooperation. International infrastructure may be expanded giving more sovereignty to the international level. This could help coordinate efforts for arms control. International institutions dedicated specifically to nanotechnology (perhaps analogously to the International Atomic Energy Agency IAEA) or general arms control may also be designed. One may also jointly make differential technological progress on defensive technologies, a policy that players should usually favour. The Center for Responsible Nanotechnology also suggest some technical restrictions. Improved transparency regarding technological capabilities may be another important facilitator for arms-control.

A grey goo is another catastrophic scenario, which was proposed by Eric Drexler in his 1986 book Engines of Creation, has been analyzed by Freitas in "Some Limits to Global Ecophagy by Biovorous Nanoreplicators, with Public Policy Recommendations"  and has been a theme in mainstream media and fiction. This scenario involves tiny self-replicating robots that consume the entire biosphere using it as a source of energy and building blocks. Nanotech experts including Drexler now discredit the scenario. According to Chris Phoenix a "So-called grey goo could only be the product of a deliberate and difficult engineering process, not an accident". With the advent of nano-biotech, a different scenario called green goo has been forwarded. Here, the malignant substance is not nanobots but rather self-replicating biological organisms engineered through nanotechnology.

Benefits

Nanotechnology (or molecular nanotechnology to refer more specifically to the goals discussed here) will let us continue the historical trends in manufacturing right up to the fundamental limits imposed by physical law. It will let us make remarkably powerful molecular computers. It will let us make materials over fifty times lighter than steel or aluminium alloy but with the same strength. We'll be able to make jets, rockets, cars or even chairs that, by today's standards, would be remarkably light, strong, and inexpensive. Molecular surgical tools, guided by molecular computers and injected into the blood stream could find and destroy cancer cells or invading bacteria, unclog arteries, or provide oxygen when the circulation is impaired.

Nanotechnology will replace our entire manufacturing base with a new, radically more precise, radically less expensive, and radically more flexible way of making products. The aim is not simply to replace today's computer chip making plants, but also to replace the assembly lines for cars, televisions, telephones, books, surgical tools, missiles, bookcases, airplanes, tractors, and all the rest. The objective is a pervasive change in manufacturing, a change that will leave virtually no product untouched. Economic progress and military readiness in the 21st Century will depend fundamentally on maintaining a competitive position in nanotechnology.

Despite the current early developmental status of nanotechnology and molecular nanotechnology, much concern surrounds MNT's anticipated impact on economics and on law. Whatever the exact effects, MNT, if achieved, would tend to reduce the scarcity of manufactured goods and make many more goods (such as food and health aids) manufacturable.

MNT should make possible nanomedical capabilities able to cure any medical condition not already cured by advances in other areas. Good health would be common, and poor health of any form would be as rare as smallpox and scurvy are today. Even cryonics would be feasible, as cryopreserved tissue could be fully repaired.

Risks

Molecular nanotechnology is one of the technologies that some analysts believe could lead to a technological singularity, in which technological growth has accelerated to the point of having unpredictable effects. Some effects could be beneficial, while others could be detrimental, such as the utilization of molecular nanotechnology by an unfriendly artificial general intelligence. Some feel that molecular nanotechnology would have daunting risks. It conceivably could enable cheaper and more destructive conventional weapons. Also, molecular nanotechnology might permit weapons of mass destruction that could self-replicate, as viruses and cancer cells do when attacking the human body. Commentators generally agree that, in the event molecular nanotechnology were developed, its self-replication should be permitted only under very controlled or "inherently safe" conditions.

A fear exists that nanomechanical robots, if achieved, and if designed to self-replicate using naturally occurring materials (a difficult task), could consume the entire planet in their hunger for raw materials, or simply crowd out natural life, out-competing it for energy (as happened historically when blue-green algae appeared and outcompeted earlier life forms). Some commentators have referred to this situation as the "grey goo" or "ecophagy" scenario. K. Eric Drexler considers an accidental "grey goo" scenario extremely unlikely and says so in later editions of Engines of Creation.

In light of this perception of potential danger, the Foresight Institute, founded by Drexler, has prepared a set of guidelines for the ethical development of nanotechnology. These include the banning of free-foraging self-replicating pseudo-organisms on the Earth's surface, at least, and possibly in other places.

Technical issues and criticism

The feasibility of the basic technologies analyzed in Nanosystems has been the subject of a formal scientific review by U.S. National Academy of Sciences, and has also been the focus of extensive debate on the internet and in the popular press.

Study and recommendations by the U.S. National Academy of Sciences

In 2006, U.S. National Academy of Sciences released the report of a study of molecular manufacturing as part of a longer report, A Matter of Size: Triennial Review of the National Nanotechnology Initiative The study committee reviewed the technical content of Nanosystems, and in its conclusion states that no current theoretical analysis can be considered definitive regarding several questions of potential system performance, and that optimal paths for implementing high-performance systems cannot be predicted with confidence. It recommends experimental research to advance knowledge in this area:

"Although theoretical calculations can be made today, the eventually attainable range of chemical reaction cycles, error rates, speed of operation, and thermodynamic efficiencies of such bottom-up manufacturing systems cannot be reliably predicted at this time. Thus, the eventually attainable perfection and complexity of manufactured products, while they can be calculated in theory, cannot be predicted with confidence. Finally, the optimum research paths that might lead to systems which greatly exceed the thermodynamic efficiencies and other capabilities of biological systems cannot be reliably predicted at this time. Research funding that is based on the ability of investigators to produce experimental demonstrations that link to abstract models and guide long-term vision is most appropriate to achieve this goal."

Assemblers versus nanofactories

A section heading in Drexler's Engines of Creation reads "Universal Assemblers", and the following text speaks of multiple types of assemblers which, collectively, could hypothetically "build almost anything that the laws of nature allow to exist." Drexler's colleague Ralph Merkle has noted that, contrary to widespread legend, Drexler never claimed that assembler systems could build absolutely any molecular structure. The endnotes in Drexler's book explain the qualification "almost": "For example, a delicate structure might be designed that, like a stone arch, would self-destruct unless all its pieces were already in place. If there were no room in the design for the placement and removal of a scaffolding, then the structure might be impossible to build. Few structures of practical interest seem likely to exhibit such a problem, however."

In 1992, Drexler published Nanosystems: Molecular Machinery, Manufacturing, and Computation, a detailed proposal for synthesizing stiff covalent structures using a table-top factory. Diamondoid structures and other stiff covalent structures, if achieved, would have a wide range of possible applications, going far beyond current MEMS technology. An outline of a path was put forward in 1992 for building a table-top factory in the absence of an assembler. Other researchers have begun advancing tentative, alternative proposed paths for this in the years since Nanosystems was published.

Hard versus soft nanotechnology

In 2004 Richard Jones wrote Soft Machines (nanotechnology and life), a book for lay audiences published by Oxford University. In this book he describes radical nanotechnology (as advocated by Drexler) as a deterministic/mechanistic idea of nano engineered machines that does not take into account the nanoscale challenges such as wetness, stickiness, Brownian motion, and high viscosity. He also explains what is soft nanotechnology or more appropriately biomimetic nanotechnology which is the way forward, if not the best way, to design functional nanodevices that can cope with all the problems at a nanoscale. One can think of soft nanotechnology as the development of nanomachines that uses the lessons learned from biology on how things work, chemistry to precisely engineer such devices and stochastic physics to model the system and its natural processes in detail.

The Smalley–Drexler debate

Several researchers, including Nobel Prize winner Dr. Richard Smalley (1943–2005), attacked the notion of universal assemblers, leading to a rebuttal from Drexler and colleagues, and eventually to an exchange of letters. Smalley argued that chemistry is extremely complicated, reactions are hard to control, and that a universal assembler is science fiction. Drexler and colleagues, however, noted that Drexler never proposed universal assemblers able to make absolutely anything, but instead proposed more limited assemblers able to make a very wide variety of things. They challenged the relevance of Smalley's arguments to the more specific proposals advanced in Nanosystems. Also, Smalley argued that nearly all of modern chemistry involves reactions that take place in a solvent (usually water), because the small molecules of a solvent contribute many things, such as lowering binding energies for transition states. Since nearly all known chemistry requires a solvent, Smalley felt that Drexler's proposal to use a high vacuum environment was not feasible. However, Drexler addresses this in Nanosystems by showing mathematically that well designed catalysts can provide the effects of a solvent and can fundamentally be made even more efficient than a solvent/enzyme reaction could ever be. It is noteworthy that, contrary to Smalley's opinion that enzymes require water, "Not only do enzymes work vigorously in anhydrous organic media, but in this unnatural milieu they acquire remarkable properties such as greatly enhanced stability, radically altered substrate and enantiomeric specificities, molecular memory, and the ability to catalyse unusual reactions."

Redefining of the word "nanotechnology"

For the future, some means have to be found for MNT design evolution at the nanoscale which mimics the process of biological evolution at the molecular scale. Biological evolution proceeds by random variation in ensemble averages of organisms combined with culling of the less-successful variants and reproduction of the more-successful variants, and macroscale engineering design also proceeds by a process of design evolution from simplicity to complexity as set forth somewhat satirically by John Gall: "A complex system that works is invariably found to have evolved from a simple system that worked. . . . A complex system designed from scratch never works and can not be patched up to make it work. You have to start over, beginning with a system that works."  A breakthrough in MNT is needed which proceeds from the simple atomic ensembles which can be built with, e.g., an STM to complex MNT systems via a process of design evolution. A handicap in this process is the difficulty of seeing and manipulation at the nanoscale compared to the macroscale which makes deterministic selection of successful trials difficult; in contrast biological evolution proceeds via action of what Richard Dawkins has called the "blind watchmaker" comprising random molecular variation and deterministic reproduction/extinction.

At present in 2007 the practice of nanotechnology embraces both stochastic approaches (in which, for example, supramolecular chemistry creates waterproof pants) and deterministic approaches wherein single molecules (created by stochastic chemistry) are manipulated on substrate surfaces (created by stochastic deposition methods) by deterministic methods comprising nudging them with STM or AFM probes and causing simple binding or cleavage reactions to occur. The dream of a complex, deterministic molecular nanotechnology remains elusive. Since the mid-1990s, thousands of surface scientists and thin film technocrats have latched on to the nanotechnology bandwagon and redefined their disciplines as nanotechnology. This has caused much confusion in the field and has spawned thousands of "nano"-papers on the peer reviewed literature. Most of these reports are extensions of the more ordinary research done in the parent fields.

The feasibility of the proposals in Nanosystems

Top, a molecular propellor. Bottom, a molecular planetary gear system. The feasibility of devices like these has been questioned.

The feasibility of Drexler's proposals largely depends, therefore, on whether designs like those in Nanosystems could be built in the absence of a universal assembler to build them and would work as described. Supporters of molecular nanotechnology frequently claim that no significant errors have been discovered in Nanosystems since 1992. Even some critics concede that "Drexler has carefully considered a number of physical principles underlying the 'high level' aspects of the nanosystems he proposes and, indeed, has thought in some detail" about some issues.

Other critics claim, however, that Nanosystems omits important chemical details about the low-level 'machine language' of molecular nanotechnology. They also claim that much of the other low-level chemistry in Nanosystems requires extensive further work, and that Drexler's higher-level designs therefore rest on speculative foundations. Recent such further work by Freitas and Merkle is aimed at strengthening these foundations by filling the existing gaps in the low-level chemistry.

Drexler argues that we may need to wait until our conventional nanotechnology improves before solving these issues: "Molecular manufacturing will result from a series of advances in molecular machine systems, much as the first Moon landing resulted from a series of advances in liquid-fuel rocket systems. We are now in a position like that of the British Interplanetary Society of the 1930s which described how multistage liquid-fueled rockets could reach the Moon and pointed to early rockets as illustrations of the basic principle." However, Freitas and Merkle argue  that a focused effort to achieve diamond mechanosynthesis (DMS) can begin now, using existing technology, and might achieve success in less than a decade if their "direct-to-DMS approach is pursued rather than a more circuitous development approach that seeks to implement less efficacious nondiamondoid molecular manufacturing technologies before progressing to diamondoid".

To summarize the arguments against feasibility: First, critics argue that a primary barrier to achieving molecular nanotechnology is the lack of an efficient way to create machines on a molecular/atomic scale, especially in the absence of a well-defined path toward a self-replicating assembler or diamondoid nanofactory. Advocates respond that a preliminary research path leading to a diamondoid nanofactory is being developed.

A second difficulty in reaching molecular nanotechnology is design. Hand design of a gear or bearing at the level of atoms might take a few to several weeks. While Drexler, Merkle and others have created designs of simple parts, no comprehensive design effort for anything approaching the complexity of a Model T Ford has been attempted. Advocates respond that it is difficult to undertake a comprehensive design effort in the absence of significant funding for such efforts, and that despite this handicap much useful design-ahead has nevertheless been accomplished with new software tools that have been developed, e.g., at Nanorex.

In the latest report A Matter of Size: Triennial Review of the National Nanotechnology Initiative put out by the National Academies Press in December 2006 (roughly twenty years after Engines of Creation was published), no clear way forward toward molecular nanotechnology could yet be seen, as per the conclusion on page 108 of that report: "Although theoretical calculations can be made today, the eventually attainable range of chemical reaction cycles, error rates, speed of operation, and thermodynamic efficiencies of such bottom-up manufacturing systems cannot be reliably predicted at this time. Thus, the eventually attainable perfection and complexity of manufactured products, while they can be calculated in theory, cannot be predicted with confidence. Finally, the optimum research paths that might lead to systems which greatly exceed the thermodynamic efficiencies and other capabilities of biological systems cannot be reliably predicted at this time. Research funding that is based on the ability of investigators to produce experimental demonstrations that link to abstract models and guide long-term vision is most appropriate to achieve this goal." This call for research leading to demonstrations is welcomed by groups such as the Nanofactory Collaboration who are specifically seeking experimental successes in diamond mechanosynthesis. The "Technology Roadmap for Productive Nanosystems" aims to offer additional constructive insights.

It is perhaps interesting to ask whether or not most structures consistent with physical law can in fact be manufactured. Advocates assert that to achieve most of the vision of molecular manufacturing it is not necessary to be able to build "any structure that is compatible with natural law." Rather, it is necessary to be able to build only a sufficient (possibly modest) subset of such structures—as is true, in fact, of any practical manufacturing process used in the world today, and is true even in biology. In any event, as Richard Feynman once said, "It is scientific only to say what's more likely or less likely, and not to be proving all the time what's possible or impossible."

Existing work on diamond mechanosynthesis

There is a growing body of peer-reviewed theoretical work on synthesizing diamond by mechanically removing/adding hydrogen atoms  and depositing carbon atoms  (a process known as mechanosynthesis). This work is slowly permeating the broader nanoscience community and is being critiqued. For instance, Peng et al. (2006) (in the continuing research effort by Freitas, Merkle and their collaborators) reports that the most-studied mechanosynthesis tooltip motif (DCB6Ge) successfully places a C₂ carbon dimer on a C(110) diamond surface at both 300 K (room temperature) and 80 K (liquid nitrogen temperature), and that the silicon variant (DCB6Si) also works at 80 K but not at 300 K. Over 100,000 CPU hours were invested in this latest study. The DCB6 tooltip motif, initially described by Merkle and Freitas at a Foresight Conference in 2002, was the first complete tooltip ever proposed for diamond mechanosynthesis and remains the only tooltip motif that has been successfully simulated for its intended function on a full 200-atom diamond surface.

The tooltips modeled in this work are intended to be used only in carefully controlled environments (e. g., vacuum). Maximum acceptable limits for tooltip translational and rotational misplacement errors are reported in Peng et al. (2006) -- tooltips must be positioned with great accuracy to avoid bonding the dimer incorrectly. Peng et al. (2006) reports that increasing the handle thickness from 4 support planes of C atoms above the tooltip to 5 planes decreases the resonance frequency of the entire structure from 2.0 THz to 1.8 THz. More importantly, the vibrational footprints of a DCB6Ge tooltip mounted on a 384-atom handle and of the same tooltip mounted on a similarly constrained but much larger 636-atom "crossbar" handle are virtually identical in the non-crossbar directions. Additional computational studies modeling still bigger handle structures are welcome, but the ability to precisely position SPM tips to the requisite atomic accuracy has been repeatedly demonstrated experimentally at low temperature, or even at room temperature constituting a basic existence proof for this capability.

Further research to consider additional tooltips will require time-consuming computational chemistry and difficult laboratory work.

A working nanofactory would require a variety of well-designed tips for different reactions, and detailed analyses of placing atoms on more complicated surfaces. Although this appears a challenging problem given current resources, many tools will be available to help future researchers: Moore's law predicts further increases in computer power, semiconductor fabrication techniques continue to approach the nanoscale, and researchers grow ever more skilled at using proteins, ribosomes and DNA to perform novel chemistry.

Works of fiction

• In The Diamond Age by Neal Stephenson, diamond can be built directly out of carbon atoms. All sorts of devices from dust-size detection devices to giant diamond zeppelins are constructed atom by atom using only carbon, oxygen, nitrogen and chlorine atoms.
• In the novel Tomorrow by Andrew Saltzman (ISBN 1-4243-1027-X), a scientist uses nanorobotics to create a liquid that when inserted into the bloodstream, renders one nearly invincible given that the microscopic machines repair tissue almost instantaneously after it is damaged.
• In the roleplaying game Splicers by Palladium Books, humanity has succumbed to a "nanobot plague" that causes any object made of a non-precious metal to twist and change shape (sometimes into a type of robot) moments after being touched by a human. The object will then proceed to attack the human. This has forced humanity to develop "biotechnological" devices to replace those previously made of metal.
• On the television show Mystery Science Theater 3000, the Nanites (voiced variously by Kevin Murphy, Paul Chaplin, Mary Jo Pehl, and Bridget Jones) – are self-replicating, bio-engineered organisms that work on the ship, they are microscopic creatures that reside in the Satellite of Love's computer systems. (They are similar to the creatures in Star Trek: The Next Generation episode "Evolution", which featured "nanites" taking over the Enterprise.) The Nanites made their first appearance in season 8. Based on the concept of nanotechnology, their comical deus ex machina activities included such diverse tasks as instant repair and construction, hairstyling, performing a Nanite variation of a flea circus, conducting a microscopic war, and even destroying the Observers' planet after a dangerously vague request from Mike to "take care of [a] little problem". They also ran a microbrewery.
• Stargate Atlantis has an enemy made of self-assembling nanorobots, which also convert a planet into grey goo.
• In the novel "Prey" by Michael Crichton, self replicating nanobots create autonomous nano-swarms with predatory behaviors. The protagonist must stop the swarm before it evolves into a grey goo plague.
• In the films Avengers Infinity War and Avengers Endgame Tony Stark's Iron Man suit was constructed using nanotechnology.