Molecule-sized robots: what is nanotechnology preparing us for?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Modern developments in the field of nanotechnology in the future will allow the creation of robots so small that they can be launched into the human bloodstream. The "parts" of such a robot will be one-dimensional and the smaller, the stronger. Dmitry Kvashnin, senior researcher at the Institute of Bioorganic Chemistry of the Russian Academy of Sciences, who is engaged in theoretical materials science (computer experiments in the field of nanotechnology), spoke about the paradoxes of the nanoworld. T&P wrote the main thing.

Dmitry Kvashnin

What is nanotechnology

Using nanotechnology, we would like to create robots that can be sent into space or embedded in blood vessels, so that they deliver drugs to cells, help red blood cells move in the right direction, etc. One gear in such robots consists of a dozen parts. One detail is one atom. A gear is ten atoms, 10-9 meters, that is, one nanometer. An entire robot is a few nanometers.

What is 10-9? How to present it? For comparison, an ordinary human hair is about 10-5 meters in size. Red blood cells, the blood cells that supply our body with oxygen, are about seven microns in size, this is also about 10-5 meters. At what point does nano end and our world begins? When we can see an object with the naked eye.

Three-dimension, two-dimension, one-dimension

What is three-dimension, two-dimension and one-dimension and how do they affect materials and their properties in nanotechnology? We all know that 3D is three dimensions. There is an ordinary movie, and there is a movie in 3D, where all sorts of sharks fly out of the screen at us. In a mathematical sense, 3D looks like this: y = f (x, y, z), where y depends on three dimensions - length, width and height. Familiar to all Mario in three dimensions is quite tall, wide and plump.

When switching to two-dimension, one axis will disappear: y = f (x, y). Everything is much simpler here: Mario is just as tall and wide, but not fat, because in two dimensions no one can be fat or thin.

If we continue to decrease, then in one dimension everything will become quite simple, there will be only one axis left: y = f (x). Mario in 1D is just long - we don't recognize him, but it's still him.

From three dimensions - into two dimensions

The most common material in our world is carbon. It can form two completely different substances - diamond, the most durable material on Earth, and graphite, and graphite can become a diamond simply through high pressure. If even in our world one element can create radically different materials with opposite properties, then what will happen in the nanoworld?

Graphite is known primarily as a pencil lead. The size of the tip of a pencil is about one millimeter, that is, 10-3 meters. What does a nano lead look like? It is simply a collection of layers of carbon atoms forming a layered structure. Looks like a stack of paper.

When we write with a pencil, a trace remains on the paper. If we draw an analogy with a stack of paper, it’s as if we were pulling out one piece of paper from it. The thin layer of graphite that remains on the paper is 2D and is only one atom thick. For an object to be considered two-dimensional, its thickness must be many (at least ten) times less than its width and length.

But there is a catch. In the 1930s, Lev Landau and Rudolf Peierls proved that two-dimensional crystals are unstable and collapse due to thermal fluctuations (random deviations of physical quantities from their average values due to chaotic thermal motion of particles. - Approx. T&P). It turns out that two-dimensional flat material cannot exist for thermodynamic reasons. That is, it seems that we cannot create nano in 2D. However, no! Konstantin Novoselov and Andrey Geim synthesized graphene. Graphene in nano is not flat, but slightly wavy and therefore stable.

If in our three-dimensional world we take out one sheet of paper from a stack of paper, then the paper will remain paper, its properties will not change. If one layer of graphite is removed in the nanoworld, then the resulting graphene will have unique properties that are nothing like those that have its "progenitor" graphite. Graphene is transparent, lightweight, 100 times stronger than steel, excellent thermoelectric and electrical conductor. It is being widely researched and is already becoming the basis for transistors.

Today, when everyone understands that two-dimensional materials can in principle exist, theories appear that new entities can be obtained from silicon, boron, molybdenum, tungsten, etc.

And further - in one dimension

Graphene in 2D has a width and a length. How to make 1D out of it and what will happen in the end? One method is to cut it into thin ribbons. If their width is reduced to the maximum possible, then it will no longer be just ribbons, but another unique nano-object - carbyne. It was discovered by Soviet scientists (chemists Yu. P. Kudryavtsev, A. M. Sladkov, V. I. Kasatochkin and V. V. Korshak. - T&P note) in the 1960s.

The second way to make a one-dimensional object is to roll the graphene into a tube, like a carpet. The thickness of this tube will be much less than its length. If the paper is rolled or cut into strips, it remains paper. If graphene is rolled into a tube, it transforms into a new form of carbon - a nanotube, which has a number of unique properties.

Interesting properties of nanoobjects

Electrical conductivity is how well or how poorly a material conducts an electrical current. In our world, it is described by one number for each material and does not depend on its shape. It doesn't matter if you make a silver cylinder, cube or ball - its conductivity will always be the same.

Everything is different in the nanoworld. Changes in the diameter of nanotubes will affect their conductivity. If the difference n - m (where n and m are some indices describing the diameter of the tube) is divided by three, then the nanotubes conduct current. If it is not divided, then it is not carried out.

Young's modulus is another interesting property that manifests itself when a rod or twig is bent. Young's modulus shows how strongly a material resists deformation and stress. For example, for aluminum, this indicator is two times less than that of iron, that is, it resists twice as bad. Again, an aluminum ball cannot be stronger than an aluminum cube. Size and shape don't matter.

In the nanoworld, the picture is again different: the thinner the nanowire, the higher its Young's modulus. If in our world we want to get something from the mezzanine, then we will choose a stronger chair so that it can withstand us. In the nanoworld, although it is not so obvious, we will have to prefer the smaller chair because it is stronger.

If holes are made in some material in our world, then it will cease to be strong. In the nanoworld, the opposite is true. If you make many holes in graphene, it becomes two and a half times stronger than non-defective graphene. When we poke holes in the paper, its essence does not change. And when we make holes in graphene, we remove one atom, due to which a new local effect appears. The remaining atoms form a new structure that is chemically stronger than the intact regions in this graphene.

Practical application of nanotechnology

Graphene has unique properties, but how to apply them in a particular area is still a question. It is now used in prototypes for single-electron transistors (transmitting a signal of exactly one electron). It is believed that in the future, two-layer graphene with nanopores (holes not in one atom, but more) can become an ideal material for the selective purification of gases or liquids. To use graphene in mechanics, we need large areas of material without defects, but such production is extremely difficult technologically.

From a biological point of view, a problem also arises with graphene: once it gets inside the body, it poisons everything. Although in medicine, graphene can be used as a sensor for “bad” DNA molecules (mutating with another chemical element, etc.). To do this, two electrodes are attached to it and DNA is passed through its pores - it reacts to each molecule in a special way.

Pans, bicycles, helmets and shoe insoles with the addition of graphene are already being produced in Europe. One Finnish firm makes components for cars, particularly for Tesla cars, in which buttons, dashboard parts and screens are made of fairly thick nanotubes. These products are durable and lightweight.

The field of nanotechnology is difficult for research both from the point of view of experiments and from the standpoint of numerical modeling. All the fundamental issues requiring low computer power have already been resolved. Today, the main limitation for research is the insufficient power of supercomputers.