2019

Small secrets: the domain of nano- and bio-technology

Deutsches Museum

Pretty tiny: How natural phenomena shape industry and our everyday lives.

Research at a microscopic level
Why does water drip off a lotus leaf? Why do the wings of an emperor butterfly appear blue from the front, but brown-spotted against the light? What is the secret of the red color of gold ruby glass? And why can a gecko walk on the ceiling without falling off? Many of the answers to these age-old questions can be found in the nanocosmos of nature, namely in the range from 1 to 100 nanometers. To illustrate how tiny this is, a single millimeter is the equivalent of one million nanometers. Today, numerous artificially developed objects bring nanotechnology into our everyday lives.

Gold leaf
More than 4,000 years ago, people were already advancing into the nanoscale when they used heavy hammers to beat gold leaf until it was wafer thin. The origins of this technique probably lie in India. One single sheet is only 100 nanometers thick. This means that to reach a thickness of one millimeter, you would have to lay 10,000 sheets on top of one another. Gold leaf has long been used to make picture frames or books—as well as furniture and icons—finer or more elegant in a cost-effective way.

Gold ruby glass
The production of gold ruby glass, a precious luxury item, has occupied alchemists and chemists since the late Middle Ages. The secret to its deep red color lies in nanotechnology The ruby red shimmer was made by finely distributed gold particles with a diameter of just 6–8 nanometers. In the rear center you can see clear gold ruby glass straight out of the furnace, while the front right shows what it looks like after being reheated to about 1112 degrees Fahrenheit, and the front left shows a cup made of this material. Behind on the right is a spiral-cut cup made of silver amber glass. Its color comes from silver nanoparticles.

The main components needed for gold ruby glass are gold, tin, and aqua regia—a mixture of hydrochloric acid and nitric acid that can even dissolve gold. The chemical process produces a dark red colorant from fine particles containing gold nanoparticles.
One of the pioneers in this field was Johann Kunckel, an alchemist and glassmaker. In the second half of the 17th century, he became famous for his beautiful gold ruby glass containers, which he produced for the Prussian king in Berlin.…

...and was honored during his lifetime by having a quatrain written about him.

The emperor butterfly
This butterfly, which lives in South America and is also known as the peleides blue morpho because of its color, does not appear blue because of color pigments, but because of the numerous grooved scales on its wings. As the distance between these grooves is mere nanometers, they swallow almost all colors—except blue. If the grooves were further apart, the butterfly would appear yellow, green, or red due to the wave spectrum of the light.

Under the electron microscope, the scales of the emperor butterfly, which are lined up like roof tiles, become visible—as do the parallel grooves running through the scales.

Geckos
They are the largest and heaviest animals that can walk up walls and upside down on ceilings without falling down. This is made possible by billions of very fine nano-sized hairs. Weak electrodynamic interactions, called Van-der-Waals forces, arise between them and the surface, enabling the gecko to hold on. The gecko moves along by rolling the hairs back, which releases them from the surface.

The lotus effect
Why does water drip off a lotus leaf? Why doesn't the plant get wet, and why doesn't it absorb the moisture? The surface of a lotus leaf is hydrophobic, which means extremely water-repellent. The leaf is coated with microfine protrusions of 5-10 micrometers in size, which in turn have a wax structure in the nanoscale. As a result, the drop has little contact surface with the leaf and, like dirt particles, is repelled by the protrusions.

The microfine protrusions are clearly visible under a microscope. Nano-fine wax hairs sprout from the protrusions and are constantly replaced. Even a drop of water the size of a pinhead covers about 10,000 protrusions on the lotus leaf. Each protrusion has about 3,000 wax hairs in contact with the drop. The drop has no chance against 30 million water-repellent hairs—it just brushes across the leaf and floats away.

Research has now succeeded in artificially creating the rough surface structure of a lotus leaf. This can be seen on the water droplet marble run.

Nanotechnology in everyday life
Without nanotechnology, many everyday objects, some of which we already take for granted, would be inconceivable.

The surface of a disposable protective suit is coated with nano-silver, which kills adhering bacteria and other microorganisms. These suits are used by fire brigades or emergency services in the event of epidemics or pandemics.

Nanotechnology is also used in the leisure industry to make clothing dirt- and water-repellent. The idea of self-cleaning abilities is taken from nature, namely from a variety of plants including the lotus flower.

This alloy wheel has a hydrophobic, or water-repellent, surface coating, which makes it easy for rainwater to rinse off dirt. As well as this, the coating increases heat and scratch resistance.

This green awning fabric in the center of the picture has a self-cleaning surface. The rough structure is created by nanoparticles embedded in a binding agent. Fluorocarbons on the surface further increase hydrophobic properties. This stops both dirt and water adhering to the awning.

The name says it all: the façade paint Lotusan in the green bucket (middle of picture) will apply a specific surface structure to the façade that will be painted. As with the lotus leaf, the contact area for water and dirt is severely reduced through combined micro- and nano-structuring. As a result, dirt particles cannot adhere to the façade and are carried away by droplets of water.

Nanotechnology at home: artificially produced, water-repellent nano-structures can be found in bathroom cleaners, waterproofing sprays or floor care products. The underside of an iron has a layer of glass a few nanometers thick to make it easier to glide over fabric and protect the steel from scratches and tarnishing from heat. Aluminum foil is coated with a protective layer a few nanometers thick, which promotes heat absorption and thus reduces cooking time in the oven by a third.

Ferrofluid
Ferrofluid is a liquid that reacts strongly to an external magnetic field. It consists of magnetic iron particles only a few nanometers in size, which are suspended in oil and do not clump together. An external magnetic field can even cause the liquid to flow upwards. Ferrofluids are most commonly used as seals, for example on millions of computer hard disks. No dust can get through— permanent magnets hold the ferrofluid tightly at the seals.

Scanning tunneling microscope
Metal plates, wires, pens, tubes, aluminum foil—but no lens like in a conventional light microscope. The device measures tiny structures and makes them indirectly visible. Gerd Binnig and Heinrich Rohrer received the Nobel Prize for Physics in 1986 for their revolutionary invention in the field of nano-research. Today, the instruments have been further developed and are used in hundreds of thousands of nano-research cases.    

The scanning tunneling microscope makes atoms visible by indirect detection. To do this, the prepared needle of the microscope is energized and the sample is carefully approached.

Shortly before the needle touches the object, a quantum mechanical effect causes a measurable current to begin to flow. This is called the tunneling current. At this distance of less than a nanometer,
the needle scans the sample line by line without coming into contact with it. Depending on the distance between the tip and the individual atoms, the measured currents vary slightly. These fluctuations are processed by computer and made into an image.
The scanning tunneling microscope makes structures up to about 0.1 nanometers, i.e. 10-10 m (0.000,000,000,1 m), visible.

Biotechnology
Some substances, such as medications, can be produced better in genetically-modified animals or plants than in cell cultures. Such a genetic modification requires oocytes or embryonic stem cells and a surrogate mother to carry the genetically modified animal. The best example of this is the highly effective production of the anticoagulant antithrombin in goats. Compared to production in a cell culture, cell density in the bioreactor of the goat's udder is up to a thousand times higher, meaning 10 grams of antithrombin can be obtained from one liter of milk. In contrast, cell cultures will only provide 0.1–1 gram per liter.

Genetic tests and gene therapies can help to alleviate diseases. They are, however, controversial. How far should we go? Should the mother of a seriously ill child be allowed to test the embryo used for in vitro fertilization to determine whether the possible sibling could act as a bone marrow donor…?

Or should the parents of a child who has died of cystic fibrosis be allowed to perform a genetic test on the unborn child in a subsequent pregnancy so they can decide whether to have an abortion if this one has a similar disease…?

Or should one carry out genetic tests in order to recognize an imminent vitreous bone disease at an early stage?

..or do tests in a pregnancy in regards to possible harm to the unborn child?

... and how do insurance companies relate to this topic?

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