An introduction to nanoscience and nanotechnology
What is a nanoparticle?
A nanoparticle is a particle between 1 and 100 nanometres in size. In nanotechnology, a particle is defined as a small object that behaves as a whole unit with respect to its transport and properties.
Nanoparticles have been around a long time having first appeared a few milliseconds after the big bang. When we small things it is because nanoparticles from the object producing the smell dissolve in our nasal cavities and are detected by olfactory receptors.
A nanoparticle can occur naturally or it can be manufactured.
It can be released intentionally or unintentionally. The Americans think that silver nanoparticles used as an antibacterial in socks is getting into lakes and seas and killing fish
Its chemical composition can be a metal, metal oxide, polymer, carbon, semiconductor, biomolecule or any other type of compound.
It can be a sphere, needle, platelet or tube shaped.
It can be dispersed in gases (aerosols), liquids (e.g. gels, ferrofluids) and solids (matrix materials). A ferrofluid is a liquid that becomes strongly magnetized in the presence of a magnetic field. A matrix material is a composite material with at least two constituent parts. When at least three materials are present, it is called a hybrid composite. An MMC is complementary to a cermet.
They can occur as nanocapsules, quantum dots, ultrafine aerosols, nanotubes, single particles, aggregates or agglomerates.
A quantum dot is a nanocrystal made of semiconductor materials that are small enough to exhibit quantum mechanical properties.
An aerosol is a mixture of fine solid particles or liquid droplets, in air or another gas.
Aggregate is the component of a composite material that resists compressive stress and provides bulk to the composite material.
Agglomerate (except in polymer science): Cluster of primary particles held together by weak physical interactions.
Agglomerate (in polymer science): Aggregate (in polymer science): Cluster of molecules or particles that result from agglomeration.
Its surface can be untreated (as obtained in production process), coated (e.g. conjugates, polymer films) or core/shell particles (e.g. spheres, capsules)
An example of a nanoparticle is a fullerene e.g. a buckyball which is a spherical fullerene molecule with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) which resembles a soccer ball, made of twenty hexagons and twelve pentagons, with a carbon atom at each vertex of each polygon and a bond along each polygon edge. It was first generated in 1985 by Harold Kroto, James R. Heath, Sean O’Brien, Robert Curl, and Richard Smalley at Rice University.
A buckyball has a diameter of 1nm and consists of 60 carbon atoms linked together in one unit.
At the moment the maths and science of nanoparticles can only be applied to nanospheres.
Nanoparticles don’t like to be on their own so they need to be treated to stop them aggregating.
To get some idea of the size of a nanosphere the ratio of the Earth to a football is equal to the ratio of the football to the buckyball.
The smallest division we can see on a ruler is 1mm. A nanometre is a million times smaller. It is a millionth of a millimetre or a billionth of a metre
A human fingernail grows 1 nanometre every second and a man’s beard grows 5 nanometres every second, the fact that you are not aware of either of these happening (although you are aware if your beard and nails need a trim) shows how small a nanometre is.
A human hair is 17 to 180 micrometres in diameter and can be seen without the use of an optical microscope. The image below shows the size relationship between a hair and nanofibres, which can’t be seen with the naked eye.
What is nanoscience?
There isn’t really an agreed definition but it is generally considered to be the study and manipulation of materials at the nanoscale.
Why bother with nanoscience?
At the nanoscale, strange things happen to materials – their properties can change.
As particles get smaller they tend to react differently with their environment than larger particles. Nanoparticles of a material show different properties compared to larger particles of the same material. Forces of attraction between surfaces can appear to be weak on a larger scale, but on a nanoscale they are strong.
One reason for this is the surface area to volume ratio. In nanoparticles this is very large. Atoms on the surface of a material are often more reactive than those in the centre, so a larger surface area means the material is more reactive.
Reactivity is the ability of atoms to interact with other atoms in their environment in a chemical reaction. It depends on the proportion of atoms on the surface of a nanoparticle with atomic bonds which are directly in contact with their surroundings.
Only the atoms at the surface of a nanoparticle have atomic bonds capable of undergoing a chemical reaction with neighbouring atoms so the smaller the particle, the greater the proportion of atoms on the surface which can react directly with their surroundings.
Smaller particles can have different optical properties: their colours change because different sizes of particle reflect and absorb light differently.
Smaller particles can have different magnetic properties than larger.
In order to understand why the reactivity changes we need to understand what an atom, a molecule, a nanoparticle and a chemical reaction is. We also need to know how the surface of a cube is calculated and how the volume of a cube is calculated.
An example of how size affects the properties is to consider which of sugar cubes and granulated sugar dissolves more quickly.
By Pallbo (Own work) [Public domain], via Wikimedia Commons commons.wikimedia.org
Incredibly the colour of gold is affected by its particle size. We are used to seeing solid gold objects look, well, gold. However the colour of gold can range from purple to red depending on the size of the atom clusters. Different sizes of particles reflect and absorb light differently.
Amazingly our medieval ancestors knew about the different colours of gold (though not knowing about nanoparticles) to make stained glass windows. Red stained glass gets its colour from nanoparticles of gold that are only 20 nanometres across and orange glass gets its colour from gold nanoparticles that are 80 nanometres across.
Potential impacts of nanotechnology
Diagnostics, Cancer treatment and targeted drug delivery.
The following slides are covered in more detail in the individual modules.
The picture below shows a nanotechnology stent, which can be used to keep arteries open or deliver drugs. The problem with stents is that they can cause a thrombosis. So it is hoped that using carbon may be the answer to this problem.
A lab-on-a chip which can do DNA analysis
Magnetic nanoparticles are a class of nanoparticle which can be manipulated using magnetic field. Such particles commonly consist of magnetic elements such as iron, nickel and cobalt and their chemical compounds. They are used in an experimental cancer treatment called magnetic hyperthermia in which the fact that nanoparticles heat when they are placed in an alternative magnetic field is used.
Another potential treatment of cancer includes attaching magnetic nanoparticles to free-floating cancer cells, allowing them to be captured and carried out of the body. The treatment has been tested in the laboratory on mice and will be looked at in survival studies.
Magnetic nanoparticles can be used for the detection of cancer. Blood can be inserted onto a microfluidic chip with magnetic nanoparticles in it. These magnetic nanoparticles are trapped inside due to an externally applied magnetic field as the blood is free to flow through. The magnetic nanoparticles are coated with antibodies targeting cancer cells or proteins. The magnetic nanoparticles can be recovered and the attached cancer-associated molecules can be assayed to test for their existence.
Cells pull in iron oxide nanoparticles (small orange circles, top left) and deposit them inside lysosomes (large yellow circle, bottom centre). Once the particles are inside these vesicles, a dynamic magnetic field causes the materials to spin and rupture the lysosome membranes (bottom right). When the lysosomes spill their contents into the cell, it triggers apoptosis, or programmed cell death.
Magnetic nanoparticles enhance medical imaging. In the below left – Non-enhanced T1-weighted image brainstem infarct (arrow) below Right – Images 48 h (D) following SPIO infusion Image courtesy of: Annals of Biomedical Engineering, Vol. 34, No. 1, January 2006 pp. 23–38.
Potential impacts of nanotechnology
Waterproof clothing such as rain jackets use nanoscience to create the waterproofing.
Effect of water repellent on a shell layer Gore-Tex jacket
Silver nanoparticles have been added to socks. This stops them from absorbing the smell of sweaty feet as the nanoparticles have antibacterial properties
Nanoparticles are also used in cosmetics such as sunscreen and anti-wrinkle creams. They offer protection and can be rubbed in so there are no white marks. Some people are not happy about this. There are some concerns that nanoparticles may be toxic to people. They may be able to enter the brain from the bloodstream and cause harm. Some people think more tests should take place before nanoparticles of a material are used on a wider scale.
Carbon fibre nanoparticles are used in sports equipment. They are added to materials to make them stronger whilst often being lighter. They have been used in tennis rackets, golf clubs and shoes.
The above right image shows Roger Federer at Wimbledon 2009 with a Wilson K Factor racquet containing silica nanoparticles and Oscar Pereiro Sio at Tour de Romandie 2007 riding a Pinarello bicycle containing carbon nanotubes. (Images: Wikimedia Commons)
Read more: Nanotechnology in sports equipment: The game changer http://www.nanowerk.com/spotlight/spotid=30661.php#ixzz3ABSLuTFe
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Potential impacts of nanotechnology
Nanotechnology is helping to develop smaller, faster and more powerful computer and mobile devices. It is being used in ultra-thin chipsets that will improve performance
Screens will be very flexible and have wall holographic projector. There will be processors up to few hundred petaflops everyday computers. This is equivalent to 300 computers all in unison. All will fit in a hand size portable laptop.
Graphene could be used for flexible touch sensitive screens and coloured ferrofluids could be used to vary screen colours.
Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. It is remarkably strong for its very low weight (100 times stronger than steel) and it conducts heat and electricity with great efficiency.
Potential impacts of nanotechnology
Nanotechnology is helping to develop more efficient ways of capturing energy from sustainable sources like the sun. It is also being used to develop more effective methods of treating water.
The above left image shows a schematic of a photovoltaic cell. Nanomaterials have the potential to enhance the performance of each layer in the cell – from more transparent coatings and more conductive electrodes to more efficient absorbers. Image credit: NREL. The above right image is a conceptual drawing of flexible OPV (organic photovoltaics) array (upper panel) and the actual device on PET (Polyethylene terephthalate) substrate (lower panel).
Dye sensitive flexible solar cells are light and easily replaceable. They can actually be applied to glass to allow windows to produce electricity.
Nanotechnology is being used to improve energy storage in the form of fuel cells, Piezoelectric scavenging devices, photovoltaics, supercapacitors and hydrogen storage.
The filter combines microbe-killing capacity with the ability to remove chemical contaminants such as lead and arsenic. Because the filters for microbes and chemicals are separate components, the system can be customized to rid water of microbial contaminants, chemical contaminants or both, depending on the user’s needs. The microbe filter relies on silver nanoparticles embedded in a cage made of aluminium and chitosan, a carbohydrate derived from the chitin in crustacean shells. The cage blocks macroscale water contaminants as well as protects the nanoparticles from sediments that would otherwise accumulate on their surfaces, thereby preventing them from releasing microbe-zapping ions.
The filters used nanoparticles that release iron- and arsenic-trapping ions to make its chemical filter. But the “cage” technique can be used with other nanoparticles to target contaminants such as mercury.
Nanotechnology is becoming increasingly important in harnessing renewable energy resources, from anti-fouling paints for wave or tidal power to materials with a higher tolerance for radiation in nuclear reactors.
In wind power, nanotechnology improves in strength-to-weight ratio of the composite materials used in blades and reduces friction in the moving parts.
The above images show wind turbines, dye sensitive solar cell and a solar power plant in Australia.
How are small things built?
Nanomaterials can be manufactured using a focussed beam of ions that can cut away materials with atomic precision.
Computer chips can be made “Top-down”– building something by starting with a larger component and carving away material (e.g. like a sculpture).
Wafer backgrinding is a semiconductor device fabrication step during which wafer thickness is reduced to allow for stacking and high density packaging of integrated circuits (IC)
Metal nanowires are made “Bottom-up”– building something by assembling smaller components (e.g. like building a car engine or Lego).
For a particle to be considered a nanoparticle at least one of the linear dimensions must be on the nanoscale.
It’s a question of size
What we want to see dictates what instruments we use
Beyond the magnifying glass
Because they only have resolutions in the micrometre range by using visible light, the light microscopes cannot be used to see in the nanometre range. In order to see in the nanometre range, we would need something that has higher energy than visible light. Louis de Broglie came up with an equation that shows the shorter the wavelength of a wave, the higher the energy it has. From the wave-particle duality, we know that matter, like light, can have both wave and particle properties. This means that we can also use matter, like electrons, instead of light. Electrons have shorter wavelengths than light and thus have higher energy and better resolution.
Louis-Victor-Pierre-Raymond, 7th duc de Broglie, (15 August 1892 – 19 March 1987)
Electron microscopes use electrons to focus on a sample. In 1926-1927, Busch demonstrated that an appropriately shaped magnetic field could be used as a lens. This discovery made it possible to use magnetic fields to focus the electron beam for electron microscopes.
After Busch’s discovery and development of electron microscopes, companies in different parts of the world developed and produced a prototype of an electron microscope called Transmission Electron Microscopes (TEM). In TEM, the beam of electrons goes through the sample and their interactions are seen on the side of the sample where the beam exits. Then, the image is gathered on a screen. TEMs consist of three major parts:
Electron source (electron gun)
System of image production
System of image recording
TEM has a typical resolution of approximately 2 nm. However, the sample has to be thin enough to transmit electrons so it cannot be used to look at living cells.
In 1942, Zworykin, Hillier, and R.L. Snyder developed another type of an electron microscope called Scanning Electron Microscope (SEM). SEM is another example of an electron microscope and is arguably the most widely used electron beam instrument. In SEM, the electron beam excites the sample and its radiation is detected and photographed. SEM is a mapping device—a beam of electrons scanning across the surface of the sample creates the overall image. SEM also consists of major parts:
Electron source (electron gun)
System of lenses
Collector of electrons
System of image production
The above left image is a scanning electron microscope and the above right image is a transmission electron microscope.
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique that measures the elemental composition at the parts per thousand range, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons that escape from the top 0 to 10 nm of the material being analysed.
Elemental analysis is a process where a sample of some material is analysed for its elemental and sometimes isotopic composition. Elemental analysis can be qualitative (determining what elements are present), and it can be quantitative (determining how much of each are present). Elemental analysis falls within the ambit of analytical chemistry, the set of instruments involved in deciphering the chemical nature of our world.
NanoSight instruments use a laser light source to illuminate nanoscale particles. Enhanced by a near-perfect black background, the particles appear individually as point-scatterers moving under Brownian motion,
Brownian motion is the random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the gas or liquid.
The above image is of a scanning electron micrograph of Heterospilus (a type of wasp).
The above image shows the results from nanoparticle counting.
The image below shows the results from XPS surface analysis of a matrix material
The above image is an optical micrograph of part of the xylem. The xylem is responsible for the transport of water and salts throughout a vascular plant.
Beyond the magnifying glass
The above image shows an atomic force microscope on the left with controlling computer on the right.
The above image shows a block diagram of atomic force microscope using beam deflection detection. As the cantilever is displaced via its interaction with the surface, so too will the reflection of the laser beam be displaced on the surface of the photodiode.
Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometre, more than 1000 times better than the optical diffraction limit.
Techniques for measuring the size of nanoparticles
Compared with the number of techniques for measuring the size of a particle greater than 1 micron, there are very few techniques that are able to accurately measure the size of small particles, particularly those less than 10 nanometres.